Hemp Growing

Analysis was con‐ ducted with correlated allele frequencies and an admixture model for K values ranging from 1 to 20. Each run was conducted with a burn‐in period of 100,000 steps followed by 100,000 Monte Carlo Markov Chain replicates. To further assess the relationships of rice samples without assumptions of specific relationship or population models, a principal component analysis of all samples was conducted in DARwin software using 99 genetic markers. In order to examine the level of differences or genetic relatedness among weedy rice biotypes and other rice groups as a whole, we looked at the pairwise fixation index among clusters of wild rice, cultivated, and weedy rice biotypes.The 99 markers used in this study covered the 12 chromosomes of rice with an average of 8 markers per chromosome and a mean interval distance of 4.43 Mb between markers. The markers showed high polymorphism with an average of 5 alleles and a mean polymorphism information content value of 0.61 per marker. In total, 508 different alleles were scored among 96 rice genotypes using the 99 markers . The presence or ab‐ sence of a 14‐basepair deletion at the Rc gene correlated with red or white pericarp in rice individuals . All weedy rice individuals had the wild‐type allele lacking the deletion, demonstrating the effectiveness of this marker for genetic identification of red pericarp in California weedy rice . In the neighbor‐joining phylogenetic analysis, individuals largely clustered by rice type . While bootstrap support for many basal branches of the tree is low, the grouping of most rice individuals into clusters by rice type is well‐supported. The cultivated japonica rice varieties were separated from indica and all other rice groups with the exception of one red‐pericarped temperate japonica variety, bud curing indicating the effectiveness of SSR markers in differentiating the two main subspecies of rice. Moreover, the tropical and temperate japonica rice varieties are well separated.

The indica rice samples, however, were not placed together, with IR29, IR64, and Milagrosa clustered together separately from red‐pericarped Pokkali landrace rice. Basmati rice, which is an aromatic rice be‐ longing to group V rice, clustered with aus rice varieties with high bootstrap support. The wild rice species samples were scattered throughout the tree as expected by the wide diversity in their genomes. The wild rice O. officinalis samples, which have a CC genome type, clustered together. The southern United States weedy rice individuals were grouped into two separate clusters, with strawhull weedy rice clustered together with high bootstrap support, while blackhull weedy rice grouped together with less support. The California weedy rice samples were grouped into four clusters, which correspond to five distinct biotypes categorized by hull color, grain type, and presence of awn . The first cluster grouped all the short grain , strawhull, awn‐ less individuals . While high bootstrap values support the grouping of Type 1 individuals, the cluster is grouped near an O. nivara individual and one temperate japonica variety as well as aus and Basmati rice with low statistical sup‐ port. The second California weedy rice cluster included all the medium grain , bronzehull, and awnless weedy rice individuals , placed near southern SH weedy rice and some wild rice. A third cluster grouped all the MG, strawhull with long awn . The single SG blackhull with long awn individual closely grouped together with the strawhull Type 3 weedy rice. The fourth weedy rice cluster grouped together some MG and long grain strawhull weedy rice accessions with variable awn length . Type 5 weedy rice was placed with high bootstrap support near the japonica rice varieties, and these two groups were placed with low support near Type 3 and Type 4 weedy rice.

The clustering of California weedy rice by grain attributes validates the division of weedy rice samples by phenotypic similarities. Two noncertified introduced cultivated red‐pericarped specialty rice varieties grown in California, , clustered with California weedy rice. These red‐pericarped cultivated rice varieties have not gone through California’s third‐party variety certification and inspection process and have been previously implicated in rice contamination . RR125 clustered within Type 2 weedy rice and RR126 clustered within MG Type 5 weedy rice, indicating that these red‐peri‐ carped specialty rice varieties are related to California weedy rices. It is unclear from this analysis, however, whether the California weedy rice could be derived directly from these noncertified varieties or whether their relationship is the result of gene flow from these varieties or their ancestors into another population. Since California weedy rice individuals clustered into distinct biotypes, genetic differences among groups of weedy rice were examined in more detail. Analysis of molecular variance indicated that California weedy rice collections are very diverse, with the majority of the variation due to differences among groups while 40% is due to variation among individuals, and differences within group or biotype account for only 5% of genetic variation . Each weedy rice biotype is genetically distinct from the others with an overall FST value of 0.548 among biotypes. Comparison of genetic diversity patterns among the four major biotypes indicate that Type 5 is the most diverse group with the highest number of alleles detected per locus , highest percentage of poly‐ morphicloci , and most heterozygous alleles . In contrast, Type 3 weedy rice has the lowest number of alleles detected per locus , lowest Shannon diversity index within group , and lowest number of heterozygotes. Type 2, which was found in four counties , is also diverse but has the highest inbreeding coefficient estimate of 0.90, indicating homozygosity of individuals in this group .

Overall, California weedy rice biotypes are genetically diverse but with a high frequency of homozygous alleles at 99 loci as indicated by high mean FIS estimate for each group or biotype as well as the overall estimates of FIS and FIT , as would be expected for a species such as rice that reproduces primarily by self‐fertilization. To investigate the relationships among rice individuals while allowing for gene flow and admixture, unlike phylogenetic analysis, STRUCTURE analysis was used to assign each individual’s genotype to genetic clusters or populations. The largest increase in data probability was observed at K = 6 , and this model distinguishes the major biotype groups fairly well . The STRUCTURE grouping of California weedy rice individuals and all other rice samples is consistent with their group membership from phylogenetic analysis . The majority of individuals assign to a single cluster with high probability, and most individuals of the same biotype assign to the same genetic cluster . However, the majority of indica rice and wild rice individuals assign to multiple clusters, indicating higher background genetic diversity or admixture between clusters. Some weedy rice individuals also assign to multiple clusters, indicating hybridization with or evo‐ lutionary origin from other rice groups. The cluster that all Type 1 individuals assign to also has minor genetic contributions from O. nivara, one indica rice variety, and some Type 2 weedy rice individuals. Some Type 2 individuals show admixture with strawhull weedy rice from the southern United States, indica rice, or wild rice species. Type 3 and Type 4 rice individuals all assign highly to a cluster that also has minor contributions from wild rice. A principal component analysis was used to assess genetic similarities among individuals without assuming spe‐ cific relationship or population models . The first three axes account for 22.9%, 11.6%, curing weed and 10.2% of genetic variation present. As in previous analyses, most rice individuals cluster together by rice type, and were spatially well differentiated on the first two axes . Type 1 rice clustered closely with aus rice, Basmati, the single temperate japonica individual that clustered separately from the others in phylogenetic analysis , and BH southern weedy rice. Type 2 weedy rice individuals clustered with SH southern weedy rice and indica rice. Type 3 and Type 4 rice clustered closely together, well differentiated on axis 2 from all other rice samples. Type 5 clus‐ tered together with temperate and tropical japonica rices. The wild rice samples did not cluster together closely, but were distributed mostly in the lower right corner. Genetic differentiation between biotypes was assessed for all weedy, wild, and culti‐ vated rice biotypes. Most estimates of pairwise FST were high, ranging from 0.177 to 0.696 . The very high pairwise FST values between the single Type 4 individual and all other groups indicate genetic differentiation but are likely artificially high due to the sample size of 1. The majority of California weedy rice biotypes, with the exception of Type 5, show high genetic differentiation from the temperate japonica rice cultivars grown in California .

In contrast, low pairwise FST between a weedy rice biotype and another rice type can indicate more shared genetic content. For example, Type 2 shows low differentiation from indica cultivars and from wild rice , indicating less differentiation between these groups and possible relatedness.The increasing spread of weedy rice in California and the recent report of weedy rice originating from cultivated California rice varieties raised questions about the origin of California weedy rice and its management. For this reason, we conducted a genetic study to understand the relationships be‐ tween existing weedy rice in California and to investigate their possible origins. In the phylogenetic analysis, weedy rice individu‐ als clustered together by biotype, indicating that for California weedy rice biotypes, samples can be easily classified by phenotype into groups that are biologically and genetically meaningful . The five biotypes of California weedy rice clustered within multiple larger genetic groups of weedy, wild, and cultivated rice . This division of weedy rice into separate clusters most likely indicates at least four separate evolutionary origins of California weedy rice from diverse lineages of cultivated, weedy, and wild rice. In fact, the four major groups of weedy rice are quite divergent from each other based on principal component analysis . Population structure analysis gives more insight into relationships of individuals and biotypes, revealing close correspondence between genetic populations and rice types . However, some rice groups, especially wild rice and indica rice, are more genetically heterogeneous, with genotypes assigning to multiple genetic clusters. STRUCTURE analysis also identified admixed individuals, indicating hybridization of weedy rice both with other weedy rice biotypes and with wild and cultivated rice , despite the fact that rice is primarily self‐fertilizing with generally low outcrossing rates . Individual and biotype differentiation analyses provide insights into the relationships of California weedy rice biotypes. The high pairwise FST values between most California weedy rice biotypes, with the exception of Type 5, and the temperate japonica cultivars widely grown in California, indicates high genetic differentiation between California weedy rice and California cultivated rice and their relatively low shared genetic content , suggesting that most weedy rice did not evolve from the cultivated rice varieties widely grown in California. The observed FST levels do not necessarily exclude the possibility of infrequent hybridization with cultivated rice within California. One Type 1 individual and one Type 2 individual showed over 10% genetic assignment to the genetic cluster containing Type 5 and japonica rices in STRUCTURE analysis . However, the majority of California weedy rice biotypes have a high inbreeding coefficient and low level of hetero‐ zygosity at 99 loci . Therefore, it is likely that hybridization between rice groups happened many years or generations ago. Type 5 weedy rice was shown in phylogenetic, STRUCTURE, and PCA analyses to be closely related to japonica cultivars, raising questions of whether it is derived directly from the temperate japonica cultivars grown in California or from tropical japonica cultivars outside California and imported. The high inbreeding coefficient of Type 5 weedy rice and moderate genetic differentiation from temperate japonica rice make it likely that its evolutionary origin significantly predates its recent detection, although it is possible that a small weedy rice population could have been present unnoticed for some time prior to detection. Another possibility for the origin and spread of California weedy rice is from the cultivation of red‐pericarped specialty rice varieties. While the majority of rice‐growing acreage in California is devoted to non-colored pericarp rice production, some specialty colored pericarp rice varieties are also grown at a commercial scale.

Lower rates seldom yield adequate forage production to justify the expense.Traditionally, nitrogen applications have been made in the fall near the time of the first rains. In regions of high rainfall and where heavy winter grazing has occurred, the forage may become extremely nitrogen deficient in the spring, even though nitrogen was applied the previous fall. Under these circumstances, spring applications of nitrogen fertilizer may be beneficial, but this practice has not been adequately evaluated on annual rangelands. Where rainfall is not great enough to leach all of the fertilizer nitrogen out of the soil, and plant nitrogen uptake is insufficient to use all of the fertilizer nitrogen, there may be a carryover response to nitrogen fertilization during the next growing season. In the 1950s, many grazing trials were conducted to demonstrate the response of range livestock gains to rangenitrogen fertilization. Carryover effects were assessed in 13 of the tests. In all but one test there was an appreciable carryover effect from fertilization, the additional gain being equivalent to about 50 percent of the first-year effects on the average. Part of the gains in these studies should be credited to the phosphorus and sulfur also applied, but the amount of credit to be given cannot be determined with the available data. Without applied nitrogen or a good stand of legumes, there is usually no response to phosphorus or sulfur on annual rangelands of California.Fertilizer can be applied from the ground or by aircraft. Large, inaccessible, rough, cannabis racks and rocky ranges are usually fertilized by aircraft. Fertilizer application equipment and tractors are usually restricted to use on rangeland where slopes are less than 20 to 30 percent and the surface is relatively free of rocks or other obstructions to the equipment.

The analysis of range sites on a given ranch during a range management planning process will help to identify those areas that can be treated from the ground and those that must be treated from the air.Fall nitrogen fertilization generally increases the protein content in annual grasses and broad-leaved forbs early in the growing season. However, an increase in protein in winter is not beneficial, since there is typically adequate protein for animal needs in unfertilized pasture at that time of year. The primary benefit from nitrogen in the early part of the season is an increase in dry matter production. As the season advances, the protein levels may decrease more rapidly in plants fertilized at moderate nitrogen levels than in those not fertilized. As a result, at the end of the growing season fertilized plants are often lower in protein than are unfertilized plants. Exceptions may occur in very dry spring seasons when moisture becomes limiting and plants are unable to grow to their full potential, thus drying up before growth dilutes the nitrogen to a low level. Yearly application of nitrogen generally increases the percentage of grasses and forbs. The particular grasses or forbs that increase will depend upon the grazing or clipping management of the pasture in question. For example, slender wild oats or ripgut brome often become dominant where nitrogen fertilizer is applied to ungrazed plots. In similarly treated plots that are heavily grazed, soft chess may become dominant. This is due to the greater tillering ability of soft chess when grazed as compared to wild oats or ripgut, which tiller poorly. Moderate to heavy grazing pressure tends to reduce the impact of fertilizer on botanical composition.Invasive species have a multitude of ecological and socio-economic effects, and can play a strong role in ecosystem functioning .

However, eradication of invasive species is expensive and difficult: globally, only ~50% of eradication attempts are successful, and success rates are substantially lower in semi-natural habitats relative to man-made environments such as greenhouses . Additionally, invasive species can become community mainstays and assume novel ecological roles in the environments they invade . In some cases, reducing invasive species can have strong habitat implications for native species of conservation concern. Therefore, if the invading species is eradicated without other restoration activities, native organisms may experience negative consequences . Scenarios like these are increasingly common around the world and present an urgent dilemma: how can natural resource managers minimize negative effects of invasive species without depleting native taxa that have come to rely on them? We address this question through our case study in the Sacramento–San Joaquin River Delta.In this case study, we examined whether water hyacinth management activities influence invertebrate communities that may support fishes of the Sacramento–San Joaquin River Delta . The Delta is part of the largest estuary on the Pacific Coast of the Americas, and serves as a critical link between California’s water supply, aquatic species, and human populations. The Delta faces many challengesthat have been described extensively by natural resources agencies and researchers . Aquatic invasive species are of great concern in the Delta because they can affect ecological communities, water distribution, commerce, recreation, and other human industries . For these and other reasons, the Delta is an ecosystem with novel features—“abiotic, biotic, and social components that, by virtue of human influence, differs from those that prevailed historically, having a tendency to self-organize and manifest novel qualities without intensive human management” .

Water hyacinth is one of the most visible invaders in the Delta, because it is a floating aquatic weed and is found nearly Delta-wide. Historically, much of the Delta, including our study location, was characterized by freshwater emergent wetlands . Vegetated littoral zones like these are important for producing invertebrate biomass as food for threatened and endangered juvenile salmonids and other fishes that forage on insects and zooplankton . However, only a small proportion of historic Delta freshwater wetlands remain today . In the absence of the once-abundant Delta littoral native plant communities, invertebrates must use available habitats. Today, the littoral habitat includes water hyacinth throughout the Delta.Water hyacinth is a floating aquatic macrophyte native to the Amazon basin. It has invaded aquatic ecosystems around the world, affecting human endeavors as well as abiotic and biotic ecosystem elements. For example, Water hyacinth can block sunlight and alter turbidity levels; decrease phytoplankton production, dissolved oxygen , and nutrient levels; and influence heavy metal concentrations . Water hyacinth can also clog navigable water ways, displace native vegetation, alter nutrient cycling, and change sediment dynamics . There is limited research that describes the role of water hyacinth in structuring and sustaining invertebrate communities. However, Villamagna et al. determined that, in general, water hyacinth increases habitat complexity but decreases food availability for invertebrates. Toft et al. demonstrated that—compared to a native macrophyte —water hyacinth had lower macroinvertebrate densities, and that the invertebrates found on water hyacinth were less prevalent in fish diets. Even so, water hyacinth has been a feature of the Delta for ~70 years, is widely dispersed, extremely abundant, and provides complex habitat for invertebrates. Given that water hyacinth is a major physical and biological feature of the Delta and serves as habitat for invertebrates that are common in the diets of some Delta fishes , it is incumbent upon Delta managers to consider the implications of water hyacinth management on the species that use it as habitat.In accordance with the Harbors and Navigation Code , the California Parks Division of Boating and Waterways is the lead agency responsible for cooperating with state, local, and federal agencies in “identifying, detecting, controlling, and administering programs to manage invasive aquatic plants in the Sacramento–San Joaquin Delta, its tributaries, and the Suisun Marsh.” In cooperation with the California Department of Fish and Wildlife, CDBW is tasked with evaluating the threat of aquatic invasive species to the environment, economy, and human health. Consequently, CDBW has undertaken programs to control water hyacinth, Brazilian waterweed , indoor grow rack and South American sponge plant in the Delta. The CDBW uses several techniques in its water hyacinth control program, including the use of herbicides . Though it is imperative that water hyacinth in the Delta be managed—given its wide distribution, ability to block navigation, rapid growth rate, and sheer abundance—weed management activities in other ecosystems demonstrate that such actions may also alter habitat, hydrology, water quality, and food resources for aquatic invertebrates that are associated with invasive macrophytes . The CDBW prepares biological assessments of their management activities—including justification of the amount of herbicide applied—for regulatory review. In an effort to reduce the environmental effects of their operations over time, they also provide logistical support for on-going research as part of their adaptive management process. Widespread herbicide application in the Delta creates a mosaic of living and decaying water hyacinth that can persist for at least 4 weeks before the decaying material dissipates.

Little is known about the macroinvertebrate communities within these decaying water hyacinth mats. It is difficult to predict how management will affect macroinvertebrates because decaying water hyacinth releases nutrients and organic particles that support the food web, but also feed bacterial communities that may drive DO down and subsequently negatively affect macroinvertabrates and zooplankton . We hypothesized that herbicide applications under current management protocols would reduce the abundance and diversity of aquatic invertebrates because they would alter structural and biological habitat.This study provides valuable information for the “evaluate and respond” component of the Delta Water Hyacinth Control Program , which employs adaptive management: a systematic approach for improving resource management by learning from management outcomes . This study also serves as a case study example for generating experimentally derived evidence to support adaptive management programs in other systems where water hyacinth is present . To ensure best practices in their management and policy operations, the CDBW has employed this work in their Section7 Biological Assessment with the United States Fish and Wildlife Service. This case study is also pertinent to management of novel ecosystems, where even non-native species can have important ecological roles . Since water hyacinth is intensively managed with herbicides on a global scale, this work has broad applicability and provides an example for future hypothesis-driven adaptive management efforts involving invasive plants’ roles in ecosystem functioning.Experimental sites were in the central Delta, California , in water hyacinth mats that surround Bacon Island . We chose to focus our study on sites that surrounded Bacon Island because they had predictable herbicide treatment dates. Other site-selection criteria included: mats of floating water hyacinth that were likely to remain in place for the study’s duration; mats at control sites that would remain untreated with herbicide; habitat characteristics similar enough to be comparable between and among treatment and control sites; and no other management activities by the CDBW.Using a Before, After, Control, Intervention experimental design, we established five sampling sites to receive herbicide treatment with glyphosate, each paired with a control site that would not receive any herbicide treatment. CDBW applied glyphosate treatments along with AgriDex at treatment locations. Treatment dates varied among sites during spring and summer 2015 . During herbicide application, the CDBW left untreated buffer strips to comply with the agency’s fish passage protocols that protect migrating and resident fish . However, for treated sites, we assumed that treatment effects would be detected throughout the site, across treated and untreated strips. To ensure this assumption matched reality, we randomly sampled across the entire spatial extent of mats at both treatment and control sites.At each site, we sampled approximately 1 month before the herbicide treatment to ensure that we had pre-treatment data. We sampled each location again approximately 4 weeks post-treatment. We used this post-treatment lag-time to ensure that herbicide effects were as uniform as possible at each of the treatment sites. Since the control locations did not receive any herbicide treatment, we describe them in terms of before and after the treatment date to indicate the point in time when herbicides were applied at comparable treatment locations. CDBW staff collected water-quality measures throughout the treatment season in accordance with National Pollution Discharge Elimination System permitting requirements using a Hach HQ30 meter and Luminescent Dissolved Oxygen probe for DO measures on the periphery of water hyacinth mats. For each sampling event, we used a numbered grid overlaid on a graphical representation of each weed mat, and a random number generator to select four portions of the mat to sample.

Fertilizer should be applied evenly over the top surface followed by a thorough irrigation to move the material into the bale . Since nitrogen levels are the limiting factor in the preconditioning process, one should select a water-soluble fertilizer high in nitrogen. As an alternative to the schedules shown in tables 1 and 2, Wilson recommended a constant liquid feed with 250 parts per million of nitrogen be used with frequent but small additions until the bales are saturated. At that point the bales are planted and liquid feed continues at every watering; 1.5 teaspoons of 24-8-16 in 5 gallons of water will approximate his method. Either organic or synthetic materials will work, but organic materials such as fish emulsion will be more expensive. Products such as fish emulsion produce a strong, disagreeable odor as the bale composts. In urban settings, this odor may be strong enough to be noticed by neighbors. Fish emulsion and other products with a similar odor can attract wildlife—particularly skunks and raccoons—that can damage the bale. Some dogs may be attracted to these bales as well and should be supervised during the conditioning process if fish emulsion is used. Figure 2 shows a bale treated with fish emulsion damaged during the night by a raccoon. Flies may also be attracted to fish emulsion when used in conditioning the bale. If animal damage occurs, replace the loose straw back into the bale firmly as soon as possible.To prepare the bale for planting, vertical growing weed apply either the full rate or half rate of the fertilizer used as determined by the preconditioning schedule you selected. Rates to use of common materials are shown in table 3. Enough variability exists between bales and gardeners’ watering practices that exact accuracy is unnecessary.

After the first 9 days of preparing the bales, once they have cooled down internally below 99°F , the conditioning process has progressed enough to plant; however, bales may not appear visually different than when the process began. A thermometer inserted into the side of the bale can be used to monitor the temperature. It is normal for this process to take 9 to 14 days. Continue to keep bales moist during this time. Figure 3 shows the recorded temperatures of two bales conditioned with 24-8-16. The composting process continues after the initial 9-day conditioning period but at a slower pace with lower temperatures than during the initial phase. Past studies of intensive wheat straw composting show this second phase can last from 20 to 37 days, after which temperatures return to ambient . It is common for mushrooms to emerge from the bale after conditioning. This is normal and is a sign of active decomposition in the bales. These mushrooms should be considered toxic and should not be eaten. Their presence will not affect your plants, but their emergence can disrupt the seed bed, interfering with germination. In low desert basins with highly saline soils, salts may be drawn upward into the bale when bales are set directly on the ground. An air gap formed by locating bales on coarse gravel or similar material will interrupt this process. Alternatively, bales can placed atop an impermeable surface such as concrete or plastic sheeting. Once the conditioning process begins, the bales should not be moved.The process of raising crops in straw bales is very similar to that used in raised bed gardening. Gardening guides such as the California Master Gardener Handbook provide cultural information for many crops; however, growing in straw bales deviates from traditional gardening in two important aspects: planting and nutrient management. Bales are usually good for only one growing season.

After that they can be used as mulch or added to a compost pile.For plants usually grown from seeds such as lettuce, squash, and carrots, an effective method of planting is to cover the surface with 2 to 3 inches of a soilless potting mix or media suitable for growth. This allows seeds to germinate in a finer-textured medium than straw. Seed planted in this prepared surface can be planted in the same manner as one would plant a traditional garden in soil or a raised bed. This method is also suitable for small transplants An alternative to starting seeds in the bale is to remove some of the bale to make a small hole. Fill this hole with a potting mix and plant seeds into the prepared area. This technique is appropriate for vegetables that form large plants, such as squash. As with any garden, plants should be spaced with enough room for them to grow. Planting suggestions for common warm-season vegetables are provided in table 4. For other crops, follow space recommendations printed on seed packets or consult a garden reference to guide you.For plants grown as transplants, remove some straw or pry apart the straw “flakes” with a garden trowel and set the transplant and its soil into the opening. Add additional potting soil to fill any gaps. Water immediately after transplanting, ensuring that both the potting soil and bale are well irrigated. Any trellises or supports should be anchored directly into the ground. As a bale decomposes, its ability to provide support diminishes, and the trellis may fall over. Bales aligned in a row with a single T-post at each end as an anchor are a good option for support and will provide additional support for the bales on the ends as they decompose. When planting bales, be sure to give consideration to how you will irrigate your crop.

Soaker hoses and drip emitters are common methods of providing water slowly to each bale. New transplants set into straw bales may dry out quickly until their roots move into the bale. Expect to water frequently while bales are still fresh. As the bales age and plants’ roots spread throughout the bale, the frequency of irrigation will diminish.Management of vegetation with fire, heavy equipment, herbicides, improved forage plants, and fertilizer played an important role in range improvement following World War II until the late 1970s. Increased fuel and fertilizer costs following the energy crisis of the mid-1970s, low prices for livestock in the 1980s and ’90s, increased liability associated with prescribed burning, the ban from the Environmental Protection Agency on the use of 2,4,5-T for brush control, requirements for environmental impact statements, and other economic and policy changes all conspired to reduce the economic return from many range improvement practices. In addition, low grazing land rental rates often made it more cost effective to rent another acre than to improve an acre. While these forces may have reduced the application of range improvement practices on California’s rangelands for the past 30 years, vegetation management remains the only practical way to increase carrying capacity or to improve wildlife habitat. Current trends of higher lease rates and limited availability of rental property due to conversion to other uses may rejuvenate interest in these practices. Vegetation management has been a continuing theme of research at the University of California since the late 1880s . Prior to the 1970s, the focus was primarily to increase carrying capacity by growing more forage and improving animal performance by increasing forage quality. Following federal and state environmental legislation in the 1970s, management for water quality, air quality, and threatened and endangered species became important management objectives on California’s and the nation’s rangelands. While increasing carrying capacity by producing more forage remains an important objective, ranchers and public agencies also manage for fire hazard reduction, improved water quality, air quality, and biodiversity. Suppressing introduced species and restoring native species has become a major theme among conservation organizations and some government agencies. In this publication, we will first identify practices that reduce seasonal gaps in forage availability and quality. Then we will discuss the economics of vegetation management. Finally, we will review brush and weed control,rangeland seeding, and rangeland fertilization practices, growing rack emphasizing the findings and recommendations of the University of California and other researchers as they have been the main source of what is known about rangeland improvement on annual rangelands.Most ranches in California combine irrigated and dryland hay and pasture with the rangeland forage base in an integrated forage system.

These additional forages are complementary to the rangeland forage base, and they increase the carrying capacity of the ranch or improve forage quality. Annual rangeland ranches depend on numerous complementary forages and feed sources to provide adequate nutrients for beef cattle and sheep production enterprises. Several common and uncommon sources of feed and forage are described below for different seasons of the year. The productive potential and feasibility of each of these sources must be adapted to the forage plant and livestock requirements, and these are dependent on the ranch’s natural, managerial, and financial resources.In this section, we will discuss the influence of vegetation management practices on seasonal forage production, forage quality, and animal performance. The range improvement practice alternatives are often applied in combination with weed and brush control to increase carrying capacity while mitigating seasonal forage gaps. For a thorough discussion of seasonal forage productivity including examples of seasonal and annual production, see the first publication in this series, “Mediterranean Climate,” and Becchetti et al. . The seventh publication in this series, “Livestock Production,” discusses seasonal forage quality and animal performance. The annual range forage year has been divided into seasons to reflect variations in productivity, quality, and animal performance. Bentley and Talbot segregated the seasons into the inadequate-green season, adequate-green season, and inadequate-dry season. George et al. and Becchetti et al. defined four seasons: fall onset of growth, winter slow growth, rapid spring growth, and summer dry. Each of these seasons has characteristic productivity limitations. The fall season is the period between the first germinating rains and the onset of cool winter temperatures. This season can be quite short to several weeks long, depending on the timing of fall precipitation and the onset of cool temperatures. During this period, the dry residual forage that was produced the previous season provides low-quality dry matter for grazing. As germination and seedling establishment progresses, the amount of new green forage increases. This new forage is high in protein and energy, but high water content may limit nutrient intake. During winter, new forage continues to grow slowly, and residual dry forage disappears due to grazing and decomposition. During the fall-winter period, low forage levels can limit intake of dry matter, energy, protein, and other nutrients. Supplementation, seeding, and fertilization can improve animal performance during the fall and winter period. Rapid spring growth begins with rising spring temperatures. During this portion of the growing season, forage quantity and quality are usually adequate for rapid livestock gains. Forage level increases rapidly and frequently outproduces the livestock’s ability to consume it. Unused forage at the end of this season remains as low-quality dry residue. Forage production and quality during this period are increased by seeding legumes and fertilization. Although not common, excess forage can be conserved as high-quality hay for future use if properly timed. Conservation of forage avoids risk associated with uncertain weather conditions, and it may increase market flexibility. However, required equipment increases overhead costs. Standing dry forage gradually shatters and decomposes, resulting in continued decline in forage quality through the summer season. This forage provides energy to grazing stock but frequently is of inadequate quality to meet other nutrient requirements. Intake of this forage is limited by its quality. It is common practice to move stock to higher elevations and irrigated pasture or provide protein and mineral supplements during this season. Strategic use of appropriate legumes can increase the quality of this dry forage. The following seasonal forage and grazing management practices can provide solutions to limitations in forage production, quality, and utilization that are manifested as inadequate animal production per acre. Controlling medusahead, goatgrass, yellow starthistle and other weeds, in combination with the seeding and fertilization that may be desirable during this season, can increase carrying capacity of annual rangeland and forage quality.In California the cost of improving an acre of rangeland has always had to compete with the cost of renting an acre of grazing land. Often it has been cheaper to increase carrying capacity by renting another acre rather than paying the per-acre cost of range improvement. However, as it becomes harder to find grazing land to lease, range improvement may become more important.

Three crop safety studies and two supplemental dose-response evaluations were conducted in 2019 and 2020 to evaluate the crop safety of the Israeli-developed PICKIT decision support system on California processing tomatoes. These studies were conducted at the UC Davis Plant Sciences Field Research Facility near Davis, California . The soil composition at this site was 41% sand, 34% silt, and 25% clay with 2.1% OM, 6.98 pH, and estimated CEC of 18.2 cmolc/kg of soil. The site did not contain broomrape; this protocol focused on crop safety of 1X and 2X rates of herbicides used in the PICKIT system that are not currently registered for use in tomato in the United States. Plots were 12 m long on 1.5 m beds with one plant line in the center of the bed. Cultivar ‘Heinz 1662’ processing tomato transplants were planted at 30.5 cm spacing. Each bed had two 15.9 mm drip lines buried at 30.5 cm with 0.6 L/hr emitters spaced every 30.5 cm; one line ran the full length of the beds and was used for crop irrigation and fertigation, the second line was terminated at the end of each plot and connected to an above-ground manifold system which was used to apply the experimental chemigation herbicide treatments. Plots were arranged in a randomized complete block design with four replications per treatment. In 2019, two experiments were conducted to represent twoplanting dates, April 25 and May 30; a single experiment was conducted in 2020 with an April 22 planting date. Pre-plant incorporated applications of sulfosulfuron were made one day before transplanting on April 24 and May 29, 2019 in the early- and late-planted experiments respectively, and on the day of planting, April 22, 2020 . PPI herbicides were applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 pounds per square inch .

PPI treatments were mechanically incorporated to 7.6 cm after application, commercial grow racks after which tomatoes were mechanically transplanted with a three-row transplanter on April 25, 2019 , May 30, 2019 , and April 22, 2020. The PICKIT system’s thermal time model is based on growing degree days , with applications at 400, 500, 600, 700, and 800 GDD after transplanting depending on treatment regimes . The PICKIT program has various regimes depending on level of infestation, with each calling for different application types and total number of applications . In 2019, chemigation applications were made through the terminated irrigation line using a 20.8 L/min 12-volt electric pump and 113.5 L tank. Treatments were applied to four plots at once, with a total carrier volume of 96.1 L per treatment resulting in approximately 15.9 L per plot . In 2020, chemigation applications were made using CO2 to inject a chemigation mix into a distribution manifold with valved connections at each plot . Treatments were applied to two replicate plots at once with separate injection ports for replicates 1 and 2 and replicates 3 and 4 to reduce the system volume receiving herbicide treated water. Herbicides were diluted in 11 L of water and this solution was injected into the already-running irrigation system over approximately 15 minutes, followed by 20 minutes ofwater to flush the distribution lines. Foliar imazapic treatments were made on July 16, 2019, August 15, 2019, and June 12, 2020 and approximately 21 days later with a backpack sprayer and two-nozzle boom delivering 280.5 L/ha with AIXR 11005 nozzles at 20 PSI. These applications were made at estimated broomrape emergence and approximately 21 days later, as these studies occurred in uninfested fields. Phytotoxicity was recorded in all three studies and representative plant height was recorded in the 2020 study. All fruit from one-meter square sections of row were harvested on September 4, 2019, September 19, 2019, and September 3, 2020 at commercial maturity and fresh weights were recorded .

Phytotoxicity, height, and yield data were analyzed using a one-way analysis of variance followed by a Tukey-HSD test using the agricolae package in R version 1.2.5033 . Two supplemental crop safety trials were conducted to evaluate increasing rates of foliar applied imazapic, which is not currently registered on processing tomatoes in California. These studies were conducted at the UC Davis Plant Sciences Field Facility near Davis, CA, . Cultivar ‘Heinz 1662’ tomatoes were transplanted on April 22, 2020 in a single plant line on a 1.5 m bed with 30.5 cm spacing. Imazapic was applied late in the growing season to simulate a rescue application in a PICKIT program. Applications were made on July 7, 2020, 73 days after transplant in the first experiment and on July 21, 2020, 87 days after transplant in the second experiment at 280.5 L/ha using a two-nozzle boom with AIXR 11003 nozzles at 28 PSI. Five rates were applied in a dose response style experiment with a 0.25% v/v nonionic surfactant . Applications were made at full fruit set . Each treatment was replicated four times in a single guard row of an existing processing tomato experiment. Visual crop injury ratings were taken 3, 7, and 14 days after treatment . Phytotoxicity means were analyzed using a one-way analysis of variance followed by a Tukey-HSD test using the agricolae package in R version 1.2.5033 .A two-year study was conducted from spring 2019 to fall 2020 to evaluate rotational crop-safety of the Israeli-developed PICKIT decision support system. This field experiment included a 2019 tomato crop treated with PICKIT herbicides followed by a planting of six common rotational crops in 2020. The study was conducted at the UC Davis Department of Plant Sciences Field Research Facility near Davis, California . The site did not contain broomrape; this experiment focused on crop safety of sulfosulfuron, imazapic, and 2X rates of imazamox, imazapyr, and imazethapyr, none of which are currently registered for use in tomato in the United States.

The 2019 tomato main plots were 54.8 m long on 1.5 m beds with one plant line in the center of the bed. Each bed had one 15.9 mm drip line at a depth of 30.5 cm with 0.6 L/hr emitters spaced every 30.5 cm. This drip line was used for crop irrigation and fertigation as well as chemigation of PICKIT treatments. For the 2019 tomato crop, main plots were arranged as whole rows in a randomized complete block design with four replications. PPI applications of sulfosulfuron were made on May 29, 2019 one day before transplanting tomatoes. PPI herbicides were applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. PPI treatments were mechanically incorporated to 7.6 cm after application. Tomato cultivar ‘DRI 319’ transplants were planted at a 30.5 cm spacing with a three-row transplanter on May 30, 2019. At each growing degree day target chemigation applications were made through the drip line using a Venturi-style injection system attached to a cone tank over the course of 45 minutes, with treatments applied to four replicate plots at once . A single one-meter square section of each plot was harvested on September 19, 2019 and total weight of all fruit were recorded . Following the tomato harvest in 2019, the tomato crop was destroyed in place with a flail mower. After the crop residue dried, beds were lightly cultivated to reshape beds but minimize soil mixing. The 54.9 m long tomato main plots were split into six 9.1 m subplots for the 2020 rotational crops in a split plot design. The six rotational crops including wheat, corn, safflower, sunflower, beans and melons were randomly assigned to a subplot such that the 2020 experimental design was a randomized split plot with four replications. On November 22, 2019, wheat subplots were planted with a grain drill. Visual wheat injury measurements were recorded during the winter of 2019 and spring of 2020. In mid-April 2020, vertical grow weed all beds were treated with glyphosate to terminate the wheat and control winter weeds in all plots and lightly cultivated to prepare a seedbed. On April 17, 2020, corn , safflower , sunflower , beans , and melons were planted using an Earthway precision garden seeder .

Plant height and fresh weight biomass were recorded nine weeks after planting on June 23, 2020; the experiment was subsequently terminated without being taken to maturity. Height and fresh biomass data were analyzed using a one-way analysis of variance followed by a Tukey-HSD test with the agricolae package in R version 1.2.5033 .A study was conducted in a commercial tomato field in Yolo County, CA, that had been reported as infested with branched broomrape in 2019 and a portion of the crop was destroyed under CDFA quarantine provisions. The infested area was prepared for planting by the grower and used for a 2020 experiment to test the efficacy of the PICKIT protocol on branched broomrape in California tomato systems. The soil composition at this site was 25% sand, 42% silt, and 33% clay with 2.7% OM, 7.2 pH, and estimated CEC of 23.6 . Plots were 30.5 m long on 1.5 m beds with two drip lines: one 22.2 mm drip line buried at 25.4 cm and one 25.4 mm drip line buried at 30.5 cm in the center of the bed. The 22.2 mm drip line was terminated at the ends of each plot serving as the dedicated chemigation line with 0.6 L/hr emitters at 30.5 cm spacing. The 25.4 mm line was used for crop irrigation and fertigation of the entire experimental area. Plots were arranged in a randomized complete block design with four replications. PPI applications of sulfosulfuron were made on March 27, 2020 . Sulfosulfuron was applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. PPI treatments were mechanically incorporated to 7.6 cm after application on the same day. In addition to the experimental treatments, the entire plot area was treated with the grower’s preplant incorporated tank mix, which consisted of S-metolachlor , pendimethalin , metribuzin , and diazinon on March 27, 2020. Cultivar ‘BQ271’were mechanically transplanted using a two-row transplanter on March 30, 2020 with two plant lines in each row with plants spaced 30.5 cm apart within and between lines. A routine foliar application of 7.2 g ai/ha rimsulfuron was made by the grower to the entire experimental area after transplanting.Chemigation applications were made using CO2 to inject the chemigation mix into 50.8 mm lay flat hose connected to valved 22.2 mm chemigation lines in each plot . Treatments were applied to two replicate plots at once; plots of the same treatment in replications 1 and 2 and replications 3 and 4 were treated together. Herbicide treatments were mixed in 11 L of solution which was injected into the already-running irrigation system over approximately 15 minutes, followed by 20 minutes of water to flush the lines. Chemigation applications were made according to a modified version of the PICKIT protocol . Foliar imazapic treatments were made with a 2-nozzle backpack sprayer delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. Broomrape scouting was done 3 times weekly for seven weeks, followed by 1 time per week for 3 weeks starting on June 1, 2020. At each rating, individual clusters of shoots were marked with wire construction flags, with different colors representing each week’s emergence . Broomrape shoot clusters were counted and recorded weekly. Total broomrape cluster numbers were analyzed using a one-way analysis of variance followed by a Tukey-HSD test in the agricolae package in R . Broomrape emergence over time was analyzed with a 3-parameter log-logistic function in the drc package in R version 1.2.5033 . Before the trial was terminated and after the final broomrape cluster count, locations of individual clusters marked by flags were recorded with a GPS device . A Trimble Handheld GPS device was placed at each flag, the coordinate was recorded in the FarmWorksMobile application , and the color of the corresponding flag was recorded. This data was entered into ArcGIS online , and a color coordinated map was created .After two field seasons and three studies, crop safety for the imidazolinone and sulfonylurea herbicides utilized in the PICKIT system appears acceptable at both the proposed rate structure and two times the proposed rate structure in California processing tomato. These results confirm the crop safety reported for the PICKIT program in Israel.

M-209 T50 was affected by planting depth in 2019, at 79 DAP and 80 DAP for 3 cm and 6 cm planting depths, respectively. Full-season plant heights were not affected by PPB treatment, cultivar or planting depth either year .In 2018 there were no harvestable panicles or yield component analysis in UTC plots. Rice yield components in weed-free plots were significantly affected by cultivar in 2018 ; all measured yield components were greater for M-209 at either planting depth. M-209 averaged 26 more florets per panicle , and 19 more filled grains than M-206 in 2018. Percent unfilled grains was 1.6-fold greater in M-209 . Although not significant, panicle yield, 1000-grain weight, total florets per panicle, and filled florets per panicle were generally greater for rice seeded at the 6 cm planting depth for both cultivars in 2018. In 2019 yield components were significantly reduced in UTC plots. Averaged across planting depth and cultivar, panicle grain yield, florets per panicle, filled grains per panicle, and 1000-grain weight decreased 47%, 31%, 37%, and 15%, respectively . M-209 planted at the 6 cm depth had the greatest reductions in yield components in 2019 UTC plots, with nearly 30% lower 1000-grain weight and 50% blanking when seeded to that depth. In 2019 weed-free plots, cultivar differences in yield components varied. Averaged across planting depths, M-206 had greater panicle grain yield and 1000-grain weight , vertical grow racks while M-209 had greater florets per panicle . M-209 blanking percentage averaged 1.7-fold greater than M-206 in 2019.Weed group composition in untreated plots did not vary between years, however weed group densities varied greatly.

Aquatic broad leaves and algae were not observed in either year, which is in agreement with previous research on DS rice using early-season flush irrigation, orfull-season alternate wetting and drying . As aquatic weeds and algae can inhibit rice growth via shading and physical barrier in water-seeded systems, the potential suppressive benefit of early-season flushing in DS rice is clear. This can be a useful component of the stale-drill method as a measure for herbicide resistance management, as algae and broad leaf suppression can occur without any additional resistance selection pressure. Grass densities were high in both study years, however Echinochloa densities were lower in 2019, allowing L. fusca and sedges to become more competitive. It is interesting that all three major weed groups were present in roughly equal numbers early in 2019 , yet Echinochloa and sedge densities decreased dramatically by 45 DAP, while L. fusca densities increased. In 2018, extreme relative density allowed Echinochloa grasses to easily out-compete other weeds and rice in UTC plots, whereas in 2019 reduced Echinochloa density allowed L. fusca to out-compete other weeds. Emergence of L. fusca is discontinuous throughout the season , and the lack of suppressive competition -particularly from Echinochloa spp.- appeared to allow later-emerging L. fusca to freely establish.Drilling rice seed at 3cm and 6 cm depths delayed rice emergence and successfully permitted the use of a postplant burndown herbicide treatment just as rice was beginning to emerge. Using flush-irrigation to prime weed seed resulted in timed emergence of the majority of observed grasses, and glyphosate use alone reduced combined grasses by more than 50% in both study years .

Although L. fusca emergence appeared to continue after PPB treatment, this was not observed with Echinochloa or sedges. Echinochloa spp. emergence is also known to be discontinuous in rice systems , however our results suggest that shallow flushing may have inhibited Echinochloa emergence from heavy soil as it dried and crusted over. Previous research showed a weed control benefit to applying pendimethalin at rice emergence, as a part of a PPB treatment . As there were no differences in further weed control between the subsequent treatments in the present study , it appears that there were no added late-season benefits of applying pendimethalin or clomazone at the 3-leaf stage. Using the stale-drill method with PPB can achieve the dual cultural-chemical effects suppressing aquatic species and shifting the weed spectrum, as well as allowing novel modes of action to be used to control grasses and sedges. Both of these effects could reduce the spread of herbicide resistance, if stale-drill is used in rotation with other rice establishment methods.Previous research found that M-206 emergence in the field was delayed by up to three extra days by planting to 5.1 cm, compared to 1.3 cm . However, emergence in that study was likely slowed by unseasonably cool temperatures immediately following planting. A related greenhouse study comparing the relative vigor four California cultivars found that M-206 planted to 5.1 cm and 6.4 cm had time to 50% emergence of 9.4 and 14.0 days, respectively. In contrast, M-209 had T50 of 8.3 and 9.4 days at the same respective planting depths . Based on these prior findings, we expected shallower-sown rice to emerge earlier, and expected M-209 to emerge before M-206. However, although there were minor differences in emerged seedling length, we found no differences in emergence date between cultivars or planting depths. The soil at the study site is a Vertisol, characterized by shrinking and cracking as it dries .

We observed that soil cracking in hot weather after the initial flushing event followed the lines of furrows left by the seeding drill. This cracking likely exposed elongating seedlings to light and oxygen, hastening emergence . Taken together, our findings support the hypothesis that California cultivars have sufficient vigor to emerge rapidly and evenly from these depths, however the increased vigor of M-209 may provide an emergence advantage if planted in cooler than normal conditions. The stand reductions at 6 cm planting depth observed in 2018 were not repeated in 2019. It is possible that physical or allelopathic effects of the much higher weed density that year inhibited some rice from establishing. The relative competitiveness of rice and Echinochloa spp. is well documented, and recent research suggests that root exudates from E. crus-galli and E. colona may have inhibitory effects on rice germination and emergence. Alternatively, growing degree day accumulation was more rapid in 2019 due to the later planting date, which may have minimized stand reductions due to deeper seeding. Nevertheless, increased tillering in M-206 compensated for stand reductions in 2018. In a related study we found increased tillering with increasing soil crown depth in these cultivars , although the opposite has been observed previously in small-seeded cereals . In addition, M-209 planted at a depth of 6 cm reached heading later than the more shallow seeding in 2019, which resulted in fewer filled grains at time of harvest.Applying glyphosate to just-emerged rice resulted in tip die-back, but no other symptoms developed. Glyphosate is a systemic herbicide, and needs to be translocated to the crown of a graminid species in order to fatally inhibit the 5-enolpyruvlyshikimate-3-phosphate synthase enzyme . Although the emerged rice seedlings were green at the time of PPB application, the lack of secondary symptoms could be evidence that seedlings were not yet translocating, and therefore still using seed reserves for growth. In addition, glyphosate in solution is anionic, and readily binds to clay soil particles, especially in lower pH soils such as found in rice systems . It is also possible that soil particles attached to the coleoptile below the emerged leaf may have protected the rice somehwat by binding glyphosate molecules. Al-Khatib et al. found that foliar uptake of glyphosate bound to particles of silt loam with 6.6 pH was less than 1% each in alfalfa and pea , and 3% in grape , compared to roughly 50% uptake of aqueous glyphosate in the same species. Grains with starchy reserves such as rice tend to tolerate anaerobic environments well , and this fact is certainly a major factor in the ability of rice organs to elongate vigorously through heavy soils or floodwaters. Alpi and Beevers found that a vigorous japonica cultivar was able to continue coleoptile elongation for up to two weeks before exhausting seed reserves. The cellular machinery in rice that is optimized for fermentative anaerobiosis also appears to provide an emergence benefit for rice grown aerobically in deep soil. Rapid and even stand emergence is key to timing a PPB treatment in deep-sown rice, and good field scouting is essential to determining emergence.

Although application of a non-selective herbicide directly to emerged rice seedlings would not be recommended, growing tables the continued reliance of just-emerged seedlings on seed reserves can provide a fail-safe against application of a normally-lethal herbicide as a burndown treatment.Differential cultivar responses to seasonal variability were apparent in this study. Trials were planted later in 2019, for a 129-day growing season versus 139 days in 2018. Although both cultivars have nominal season durations of about 140 days , M-209 is slower to mature than M-206, reaching 50% heading about six days later in traditional WS rice culture. M- 209 reached 50% heading eight days later than M-206 in 2018, but only 3-4 days later in 2019, reflecting a T50 shift of 3-4 DAP in 2019 . As the rice was planted later in the summer, growing degree day accumulation would be expected to be greater early in the season, resulting in panicle initiation occurring earlier than expected in M-209. This possibility, along with the shortened season duration, may explain why M-209 appeared to have higher sensitivity to seasonal fluctuations than M-206.We find that the present study serves as a successful proof-of-concept for the stale-drill method as a new strategy for rice production and weed management. This work agrees with previous studies that suggested that California semidwarf rice cultivars possessed suitable vigor to emerge evenly from seeding depths up to 6 cm, and that a PPB application of a non-selective herbicide could be safely administered to emerging rice without causing sustained crop injury. Aquatic weeds were suppressed by water management, and the PPB treatment reduced overall weed density by more than 50% in both years, regardless of planting depth or cultivar used. Variability in observed effects of deeper planting on rice growth and development do not support planting rice deeper than 3 cm, however. Although the two cultivars used in this study have varying levels of observed responses to seasonal variability, adequate field preparation, irrigation management, variety selection, and scouting can help to ensure healthy and economically competitive stands. In order to validate our confidence in this method, field-scale trials analyzing the logistical and economic parameters of implementing this program across soil and climate types are necessary. In addition, further refinements to herbicide programs emphasizing reduced input costs, and the potential of reducing seedbanks of weedy rice and herbicide-resistant weeds, would help to more adequately assess the flexibility and potential utility of this method.Glyphosate-resistant crops, also known as “Roundup Ready” , have become an important part of cropping systems in the United States. In 2004, approximately 13 percent of corn, 85 percent of soybean, and 60 percent of cotton acreage was occupied by RR varieties. Alfalfa is the nation’s third most important crop in economic value, and it occupies more than 22 million acres in the United States . It is considered the premier forage crop. It is the primary feed for dairy production, and is commonly fed to beef cattle, sheep, and horses. Alfalfa is also used for green chop and silage in many areas. California is the leading producer of alfalfa hay in the United States, followed by Wisconsin, South Dakota, Minnesota, and Idaho. Roundup Ready technology has been successfully incorporated into alfalfa and is scheduled for commercial release in 2005. This publication reviews the important attributes and issues pertaining to RR technology as applied to alfalfa and the potential impacts of this technology on production systems and markets.Roundup is a broad-spectrum herbicide that kills a wide range of plants. It is not normally applied directly to crops. The RR technology incorporates genetic resistance to glyphosate into crop plants by inserting a single bacterial gene that modifies 5-enolpyruvylshikimate-3-phosphate synthase, an enzyme essential for plant growth. Monsanto has used this technology to develop several RR crops . Specifically, these new varieties will allow glyphosate to be applied over the top of the entire crop to control a wide spectrum of annual and perennial weeds commonly found in alfalfa. Several of these weeds, especially perennials, are difficult to control using conventional herbicides or non-herbicide weed control methods.

The effects of herbicide application timing on Echinochloa densities in 2016 were only significant for T5; however, Echinochloa density was generally greater in plots with deeper-seeded rice. In 2017, Glyphosate alone reduced Echinochloa density by 30%, 31%, and 73% in 1.3 cm, 2.5 cm, and 5.1 cm planting depths, respectively, while glyphosate f.b. pendimethalin reduced Echinochloa density by 58%, 66%, and 80%, across the same depths. All other treatments reduced Echinochloa density by 87% or more. Treatment timing only effected Echinochloa density in T3 and T4 in 2017. L. fusca densities were lower than those of Echinochloa in either year . Treatment effects on L. fusca density were only apparent at 1.3 cm rice planting depth either year, with T4 having the highest density of 37 L. fusca plants m-2 in 2016, and 48 plants m-2 in 2017. T4 was also the only treatment with significant timing effects on L. fusca density, with lower density at greater rice planting depth either year. Sedge densities in 2016 were affected by herbicide treatment at each rice planting depth. Glyphosate alone reduced sedge density from UTC by 40%, 23%, and 86% in 1.3 cm, 2.5 cm, and 5.1 cm rice plantings, respectively, while glyphosate f.b. pendimethalin reduced sedge density by 74%, 45%, and 86% over the same planting depths. Treatments with POST herbicides reduced sedge density the most at any rice planting depth, with an average 95% reduction.Maximum air temperature at seeding was 21.8°C in 2016, and increased to greater than 30°C by the time of rice emergence . In 2017, the maximum air temperature at day of seeding was27.5°, however, the following day saw 15.2 mm of rainfall, growing rack and maximum temperature fell to 19.4°C, remaining below 25°C for several days. Rice began to emerge from 1.3 cm planting depths seven days after planting in 2016, and 8 DAP in 2017 .

Planting rice deeper than 1.3 cm delayed stand emergence similarly in both years; emergence for rice planted to 2.5 cm and 5.1 cm was delayed by three and four days, respectively. Time to 50% heading was also delayed by 1-2 days for rice planted to 2.5 and 5.1 cm. Applying glyphosate just as rice was beginning to emerge did not result in any observable crop injury in either year. In 2016, overall rice stand establishment was not affected by herbicide treatment or planting depth, although stands generally decreased with planting depth, averaging 178, 119, and 101 plants m-2 at 1.3 cm, 2.5 cm, and 5.1 cm depth, respectively, averaged across herbicide treatments. Untreated plots in 2017 were exceptionally weedy; therefore, the rice stand was impossible to estimate for UTC plots at 2.5 cm and 5.1 cm planting depths. Nevertheless, there were no stand differences among treated plots at any given seeding depth in 2017. Planting depth did affect rice stands in 2017, however. Stands in treated plots decreased by an average 89% and 96%, at 2.5 cm and 5.1 cm depths, respectively. Rice tiller density was significantly affected by herbicide treatment and planting depth in both years . Across planting depths in 2016, tiller density was 1.6 times greater than in UTC for glyphosate alone and glyphosate f.b. pendimethalin , increasing to 2.4 times greater than UTC with T5. Tillering in 2016 decreased by an average of 19% in deeper plantings. In 2017 tiller density was greatest with T5 at 1.3 cm depth, and lowest in UTC plots at 5.1 cm depth. Compared to 1.3 cm planting depth, tiller density in treated plots decreased by 60% and 56% at 2.5 cm and 5.1 cm depths, respectively in 2017.Rice plant heights were affected by herbicide treatment in both years , however, no planting depth effects were observed in 2016. In 2016, plant height was generally higher in T3, T4, and T5, averaging 95 cm, whereas plants in UTC, T1, and T2 averaged 87 cm.

In 2017 rice heights decreased as planting depth increased. Plant heights in 2017 were greatest in T3, T4, and T5, averaging a combined 93 cm, 91 cm, and 85 cm at 1.3 cm, 2.5 cm, and 5.1 cm planting depths, respectively. Yield components were largely unaffected by herbicide treatment or planting depth in 2016 , however, in 2017 differences in panicle grain yield, number of florets, and unfilled florets were apparent. In 2017 there were no harvestable panicles in UTC plots seeded at 2.5 cm and 5.1 cm planting depths, or in T1 plots seeded at the 5.1 cm depth. In either year, panicle grain yields were generally higher in less-weedy plots, particularly in plots with POST herbicides . Planting depth effects on panicle yield were likewise only apparent in weedier plots . Thousand-grain weights were lower UTC plots either year, although there were no differences among treated plots or planting depths. In both years, florets per panicle were greater in less-weedy plots, particularly with T3, T4, and T5. Florets per panicle in less-weedy plots also increased as planting depth increased. Floret filling appeared to be little affected by plot weediness or planting depth either year, and observed differences in unfilled florets were inconsistent. Both florets per panicle and unfilled florets were generally greater in 2017 than in 2016. Rice yield was significantly affected by herbicide treatment in both years , but was less influenced by planting depth in 2016 than in 2017. In either year, yields were generally greater in less-weedy plots. In 2016, yields in plots treated with glyphosate alone were 2.4-fold, 3.6- fold, and 1.7-fold greater than UTC in 1.3 cm, 2.5 cm, and 5.1 cm plantings, respectively, while yields in plots treated with glyphosate f.b. pendimethalin increased 2.9-fold, 4.4-fold, and2.6-fold over UTC, at the same planting depths.

In 2017, yields were generally higher in plots that received POST herbicides , though yields decreased as planting depth increased. Additionally, in 2017 yields in plots planted to 2.5 cm and 5.1 cm depths, and treated with T3, T4, and T5 decreased from those at the 1.3 cm planting depth by 48%, 28%, and 24%, and by 67%, 72%, and 54%, respectively.The aim of this study was to assess the feasibility of combining a stale seedbed with deep rice seeding depth, as a means to accommodate a non-selective weed burndown treatment without delaying planting. If implemented correctly, this post plant-burndown method may provide a novel cultural tool for combatting herbicide resistance in rice. Deep-seeding of rice sufficiently delayed stand emergence to allow a PPB of glyphosate without injuring rice stands. However, burn down timing effects on weed density varied by year. In 2016, Echinochloa control with glyphosate PPB alone was reduced at deeper rice plantings. Given that PPB treatments were timed to rice emergence, we expected to see greater Echinochloa control as PPB application was delayed in deeper-seeded plots. However, in 2017 delaying PPB by 5 days in the 5.1 cm planting depth plots did reduce Echinochloa density considerably, even though Echinochloa pressure was far greater that year. It is possible that the added PPB treatment delay in 2017 afforded more time for grasses to emerge and be controlled with the treatment. As Echinochloa plants were not reduced 100% by glyphosate PPB alone in any depth or year, it is evident that Echinochloa emergence is nonsynchronous at the study site, which is in agreement with previous studies . Nonsynchronous emergence may provide some insight into the inconsistent effects of PPB treatment delay with greater rice planting depth. It is also interesting that in both years, Echinochloa densities in T3 through T5 were higher with increasing rice planting depth. It is likely that reduced rice stands in these plots resulted in concomitant reduced competition from rice, potentially allowing more Echinochloa seedlings to establish . In addition, delayed flooding at 2.5 cm and 5.1 cm planting depths may also have allowed later-emerging weeds to avoid flooding suppression. Echinochloa pressure was considerably higher in 2017 than in 2016, which had significant effects on the relative competitiveness of L. fusca and sedges. Grasses in general are the most competitive weeds in DS rice , hydroponic rack system but Echinochloa tend to emerge earlier and more vigorously than sedges and L. fusca , and can easily dominate fields where control measures are inadequate.

In either year, high Echinochloa densities in UTC, T1, and T2 plots effectively suppressed L. fusca, accounting for discrepancies between visual control estimates at 20 DAP, and weed density counts at 60 DAP. However, L. fusca was more competitive in T3 and T4 at 1.3 cm planting depth, reflecting reduced Echinochloa density, and the lack of an effective POST herbicide for L. fusca in those treatments. L. fusca can become a dominant species when Echinochloa and sedges are suppressed in DS rice systems . Delaying PPB application at 2.5 and 5.1 cm depths in T3 and T4 appeared to enhance L. fusca control, however, therefore PPB treatments afforded by planting rice deeper can aid in L. fusca management efforts, particularly in fields where L. fusca resistance to cyhalofop may a problem . Planting rice deeper than 1.3 cm delayed stand emergence by several days, although the differences between 2.5 cm and 5.1 cm planting depths were minor. This is not surprising, as rice seedlings elongate quickly in soil once seed reserves are mobilized . In a related study of California rice cultivars, below-soil seedling elongation for the most vigorous cultivars increased markedly after 6 DAP , resulting in reduced emergence delays as planting depth increased. In either year, stand establishment tended to decrease with greater planting depth, however, stand establishment with deeper seeding was much lower in 2017, as several days of cooler weather coincided with planting in 2017. Colder temperatures can reduce seedling vigor and slow elongation in heavy soil. A related study found that lower-vigor California rice cultivars continued to emerge at low rates after 21 DAP . It is therefore possible that cool weather just after planting in 2017 slowed emergence of deeper-seeded rice, resulting in final rice stands somewhat larger than those measured at 20 DAP. In WS systems, rice is typically seeded at 170 – 200 kg ha-1 to overcome seed loss due to wind or predation. Drilling seed at a higher rate may likewise overcome stand and tillering loss from deeper planting in staledrill systems. In either year, rice tiller density was reduced by a lesser degree than stand density, by either treatment or depth. Tillers per plant would be expected to increase as stand density decreases , reaching up to 5-6 tillers per plant with California cultivars. However, comparing tiller and stand densities for deeper plantings in 2017 suggests up to ten tillers per plant by 60 DAP, which seems unlikely and further suggests a weather-induced delay of rice emergence, as noted above. Ultimately, although tiller density in treated plots decreased at depths greater than 1.3 cm, planting-depth effects seem to diminish between 2.5 cm and 5.1 cm depths, in accordance with a related study on depth effects on California rice .Glyphosate alone and glyphosate f.b. pendimethalin provided sufficient weed control to limit yield reductions due to weed competition to 23 – 65% in 2016, however, in 2017 yield reductions in those treatments were up to 100%. Planting rice deeper than 1.3 cm did not have an effect on yields in 2016, but yields were reduced with increased planting depth in 2017. Yield decreases in 2017 were greater than tillering decreases, suggesting that tiller die-off in deeper plantings reduced final panicle density that year. As panicle yields and 1000-grain weights were consistent across years for the less-weedy plots, it is apparent that planting depth does not affect grain quantity or 1000-grain weight. It is interesting that both florets per panicle and unfilled florets were both higher overall in 2017, resulting in similar filled grains per panicle in both years. Higher temperatures can play a role in increasing florets per panicle , while cooler nighttime weather during anthesis can cause sterility in rice , yet there were no such phenomena in 2017 to explain the elevated florets per panicle or percentage of unfilled florets.Rice [Oryza sativa L.] is grown on about 200 000 ha in northern California . Due to its hot, dry summer climate, the CA rice environment is especially conducive to competitive grass weeds, particularly Echinochloa species. For this reason, CA rice is predominantly water-seeded, in order to suppress the growth and emergence of grasses . In water-seeding, pregerminated rice seed is broadcast by aircraft into permanently flooded basins, where the seed settles on the soil surface and pegs-down roots.

The four almond kernels that were tumbled directly in the [14C]- herbicide treated soil were rinsed with 20 mL of water. The rinsate was collected into glass scintillation vials and evaporated to near dryness using vacuum evaporation. 10 mL of Ultima Gold™ was added to the scintillation vial and analyzed using the liquid scintillation counter. The rinsed kernels were homogenized and combusted; the combustion product was mixed with scintillant and analyzed using the liquid scintillation counter.To examine the glyphosate and glufosinate residues in almonds at different pre-harvest intervals a field study was conducted in a mature almond orchard at The Nickels Soil Laboratory located near Arbuckle, California, United States. The orchard included full rows of nonpareil almonds alternating with rows of several pollinizer varieties; trees were planted 4.9 m apart within the rows and rows were 6.7 m apart. The experiment was conducted in the nonpareil rows and treatments were organized into a randomized complete block design with four replicates. Herbicide treatments included a single herbicide mix applied at timings that correspond to PHIs of 35, 21, 14, 7, and 3 days before shaking. Each plot was 19.6 m long by 4 m wide and contained four almond trees; the width of each herbicide plot started from one side of the tree trunk and extended 4 m, nearly to the nexttree row . The herbicide treatment for all plots was a tank mix of commercial glyphosate at 1,681 g ae ha-1 , harvest drying rack commercial glufosinate at 1,681 g ai ha- 1 , nonionic surfactant at 0.25% v/v , and AMS at 1% v/v .

Applications were made using a CO2 pressurized backpack sprayer with a 2 m boom equipped with four air induction extended range nozzles calibrated to deliver 187 L ha-1 at a pressure of 207 kPa. At each application date, previously fallen almonds were counted in two 1 sq m areas in each plot. On the day of harvest, the middle two almond trees of each plot were hand shaken using mallets and poles, then the nuts were left on the orchard floor to dry. Approximately 100 g of surface soil was collected from each plot at this time for herbicide analysis prior to sweeping. Three days after shaking, the nuts were swept into a windrow between tree rows in approximately the center of the herbicide-treated plots using a commercial self-propelled mechanical sweeper. Four days later approximately 500 g of nuts were collected from each plot windrow, separated by hand from the soil and other debris, and stored frozen until further analysis. This timeline corresponds to typical commercial harvest practices. At almond sampling, approximately 100 g of surface soil from each plot was also collected for herbicide analysis post sweeping.A summary of the glyphosate residues is presented in Table 2. Total glyphosate concentration is presented as the sum of glyphosate, AMPA, N-acetyl-glyphosate, and N-acetylAMPA. There were no statistically significant differences in concentration of glyphosate or total glyphosate found in the hull and shell samples. N-acetyl-AMPA was found only in almond hull samples. The almond hulls had the highest detection of glyphosate and its metabolites, averaging 0.174 mg kg-1 , while still being well below the US MRL. The almond shell samples were above the EU almond kernel residue limit of 0.1 mg kg-1 however, in practice, in shell almonds are shelled before residue analysis.

PHI within the tested range did not have a statistically significant effect on glyphosate residues in hull and shell samples. A summary of the glufosinate residue data is presented in Table 3. Total glufosinate concentration is presented as the sum of glufosinate, N-acetyl-glufosinate, and MPP. There were no significant differences in residues found in hulls, shells, or kernels and these samples were all below the US MRL for total glufosinate. The EU total glufosinate MRL was exceeded in almond shells in at least some replicate plots at 3-, 14-, 21-, and 35-day PHIs. MPP was the only compound detected in almond kernels at PHIs of 3, 14, 21, and 35 days. Although the three- and seven-day PHIs were off-label applications of glufosinate, there were no significant differences in glufosinate residues among the PHI treatments. Glyphosate and glufosinate are generally considered to have moderate and short soil halflife, respectively and the almond orchard soil samples collected from the orchard floor support that degradation pattern. Total glyphosate concentrations remained consistent, apart from an anomalous 7-day pre-sweep value, across all PHIs and pre- and postsweep samples; the range of total glyphosate in samples taken prior to sweeping was 2.331 to2.575 mg kg-1 and the range in samples taken after sweeping was 1.536 to 3.554 mg kg-1 . The half-life of glyphosate in soil ranges between seven and 60 days depending on soil properties and given samples were taken from the soil surface that was dry due to preharvest management practices it is expected the half-life would be closer to the high end of the given range. Total glufosinate concentration in the soil followed a decreasing trend from the PHI of three to 35 days with the majority of the total glufosinate concentration being attributed to MPP . Total glufosinate decreased from 5.339 to 0.210 mg kg-1 in the pre-sweep samples and from 7.687 mg kg-1 to less than the detection limit in the post-sweep samples .

Glufosinate is rapidly degraded by soil bacteria and has a half-life between three and seven days; the main degradation product is MPP . The 7-day pre-sweep sample appears anomalous and likely from a sample processing error in the unreplicated sample since there was no correspondingly high values in the almond samples from those plots . The current labels state the minimum PHI for glyphosate and glufosinate is three and 14 days, respectively. The field results showed that increasing the PHI up to 35 days before shaking did not appear to substantially reduce the amount of glyphosate or glufosinate in the samples. Total glyphosate residues in kernels from almonds sampled in the windrow were below the limit of detection at every PHI tested . At the minimum 14-day PHI total glufosinate residues in kernels from almonds sampled in the windrow were 0.037 mg kg-1 while the 35-day PHI residues were 0.089 mg kg-1 ; these data were not statistically different . Based on these data we conclude increasing the PHI of the herbicides within a range of utility for preharvest operations is unlikely to significantly contribute to lower residue levels.Prior to conducting these experiments, one almond industry concern was windfall nuts that are directly sprayed with herbicide contaminating the whole batch. Windfall nuts typically account for zero to 1% of the total harvest and nuts that fall greater than four weeks prior to harvest are usually of poor quality because of immaturity or degradation processes. The number of potentially directly-treated almonds was relatively low in this study and the earliest falling and mostly likely to be directly treated would likely be removed from the batch during processing based on the United States Department of Agriculture grading standards for size, damage, and color . The almond-to-almond transfer experiment in the lab suggested low transfer of glyphosate or glufosinate from treated to untreated nuts; therefore, the small portion of directly sprayed windfall nuts that make it through the processing facility are unlikely to have high enough residues to elevate the batch residues above the MRL. Almond hulls, shells, and kernels were below the United States MRLs for both glyphosate and glufosinate as well as their metabolites. If the EU reduces the MRL further based on new hazard and risk assessments, this will pose a challenge to California growers when choosing preharvest herbicides. It is worth noting the almonds in both the field and lab experiments presented here were not commercially processed and, thus were not subjected to mechanical and pneumatic cleaning and sorting operations to remove soil and debris; these steps likely would have more effectively removed the soil particles and soil-associated herbicides compared to these research samples.

It is also recognized that the limits of detection of the analytical instrumentation methods used are higher than the recommended new MRLs for glyphosate and its metabolites. Future research will focus on pesticide residues at the later points in almond processing and include sampling almonds and soil particles at various points within a commercial hulling and shelling facility.California produces 80% of the world’s almonds, vertical growing racks and the crop is the most valued export commodity from the state, generating $4.9 billion in export revenue in 2019 . Currently there are more than 500,000 ha of bearing almond trees in California producing over 1.3 billion kilograms of almonds annually . Almonds are mechanically harvested by shaking the trees, sweeping the nuts into windrows, and finally picking up the nuts from the orchard floor. Weeds on the orchard floor can reduce harvest efficiency by interfering with harvest equipment, so many growers utilize relatively intensive herbicide programs to maintain bare ground prior to harvest . Glyphosate and glufosinate are two commonly used herbicides for preharvest programs because of their broad-spectrum weed control and relatively short preharvest intervals , three and 14 days respectively . In 2018, over one million kg of glyphosate and nearly 300,000 kg of glufosinate-ammonium were applied in California almond orchards . Because of the harvest methods there is ample opportunity for whole almonds to come into contact with herbicide-treated soil. After almonds are collected from the field, they are usually stockpiled under plastic covers before being transported to a processing facility for hulling and possibly shelling. At the huller/sheller, almonds are processed in large batches through rollers and gravity tables as well as pneumatic and sieve separatory equipment to remove dirt, debris, and hulls. These processes produce inshell almonds or include further steps to also remove shells to produce shelled almonds . Contact with contaminated processing equipment, almonds, and debris could provide another avenue for pesticide residue contamination.California exports about two-thirds of its almond production annually , with most of the product shipping as shelled almonds . Historically, the European Union has been the largest importer of California almonds with over 50% of the shelled product going to the EU whereas the largest importer of in shell almonds is Asia . Exported shipments of almonds are subject to pesticide residue testing by the importing country’s food safety authority, and residues must be at or below the maximum allowable concentration. The maximum residue limit , commonly called tolerances in the United States , is defined by the Food and Agriculture Organization of the United Nations as the maximum allowable concentration of pesticide residue to be legally permitted in food commodities and animal feed . In the US, glyphosate and glufosinate MRLs are defined to include the parent compounds and the primary metabolites . For clarity, these MRLs will be referred to as “total glyphosate” or “total glufosinate” if the concentrations of the metabolites are to be summed with the concentration of the parent compound. The US MRL for total glyphosate in almond hulls is 25 mg kg-1 and 1 mg kg-1 for kernels. There is not a separate US MRL for in shell almonds because the residue in in shell almonds is determined by shelling the almonds and measuring the residue in only the kernels. The US MRL for total glufosinate in both almond hulls and kernels is 0.5 mg kg-1 . In the EU, the MRL for glyphosate is 0.1 mg kg-1- in almond kernels but there are not established MRLs for glyphosate metabolites. The EU MRL for glufosinate includes its metabolites N-acetyl glufosinate and 3-propionic acid ; the MRL for total glufosinate is 0.1 mg kg-1 .Glyphosate is registered in the EU until 2022 . A review completed by the European Food Safety Authority recommended that the MRL for parent glyphosate be reduced to 0.05 mg kg-1 and an optional total glyphosate MRL for the summation of glyphosate and its primary metabolites, a-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid and N-acetyl-glyphosate, set to 0.2 mg kg-1 . It is anticipated that in upcoming years glyphosate MRLs will be reduced, and it is a possibility that the chemical may not be re-registered. If at any time the safety of a current MRL is reconsidered, the MRL can be reduced to the lowest limit of analytical detection which currently is 0.01 mg kg-1 , according to European statute .

It was hypothesized that, as the water treatment pH increased, there would be greater removal of herbicide from the soil in the rinsate. As pH of the solution increased, the equilibrium of the weak acid herbicide would be pushed towards the anionic herbicide form resulting in lower sorption to the soil and greater removal in the rinsate. However, the opposite trend occurred for two of the herbicides . As water treatment pH increased, the concentration of saflufenacil and penoxsulam decreased in the aqueous solution extracted from the soil. Saflufenacil removal in the rinsate was greatest at pH 5 with about 78% and lowest at pH 8 with about 64%. At pH 5, about 35% of the penoxsulam was removal from soil and this decreased to about 22% removal at pH 8 . Indaziflam was below the detection limit of the instrumentation in all rinsate samples, regardless of pH.The results of the EC water treatments show that, as EC increased, herbicide removal decreased slightly . The effect of ionic strength on ionizable pesticide adsorption to soil has been well documented12; the common trend is that as ionic strength increases, the pesticide adsorption also increases . These data support that trend as well. The greatest amount of saflufenacil and penoxsulam was removed from soil in the 0.5 dS m-1 water solution rinse; about 70% of saflufenacil was removed from soil and about 25% of penoxsulam was removed. Meanwhile, weed dry rack in the 1.5 dS m-1 and 3.5 dS m-1 solutions, approximately 65% of saflufenacil and 22% of penoxsulam was removed . Indaziflam was below the detection limit of the instrumentation in all rinsate samples regardless of ionic strength of the rinse solution.

Indaziflam was below the detection limit in all samples; however, it is not clear if this is due to strong sorption to soil or to degradation processes. While indaziflam is considered moderately mobile to mobile in soil14, it does have a higher Koc range than saflufenacil or penoxsulam23 meaning indaziflam would be more strongly sorbed to soil than the other herbicides in this study. Indaziflam has been reported to undergo photolysis in aqueous solutions rather quickly 14; samples were stored in the dark for much of the duration of the experiment. A brief follow-up experiment confirmed the laboratory lights did not cause photolysis of the chemical in aqueous solution under the conditions of the experiments . Saflufenacil dissipates relatively quickly in the environment23. The herbicide has biotic and abiotic degradation pathways but the most relevant pathway to this study would be hydrolysis in alkaline water13. The data set shows a significant decrease in herbicide removal from soil from pH 5 to pH 6 and 8 . The pH 7 data point was not statistically different from the other pH water treatments. There have been differing reports on penoxsulam hydrolysis. The Environmental Protection Agency states that penoxsulam is stable under hydrolysis conditions15 while Jabusch and Tjeerdema report triazolopyrimidine sulfonamide herbicides do undergo hydrolysis and the rate is dependent on pH24. There have been studies completed on two other herbicides in the TSA class which support pH dependent hydrolysis rates25-26. Given that the experimental samples were held at field capacity for seven days in this study, pH dependent hydrolysis could explain why penoxsulam concentrations were decreasing from 34% removal from soil at pH 5 to 22% removal at pH 8 .Adsorption mechanisms of pesticides are difficult to define because of the complex interactions between the soil surface, soil solution, and pesticide. Additionally, it is likely more than one adsorption mechanism occurs.

There are several mechanisms by which weak acid pesticide adsorption could be positively influenced by ionic strength – cations could displace hydrogen atoms from the soil surface resulting in a slight pH decrease that would favor a neutral pesticide form, more cations could be available to bridge the anionic form of the pesticide to the negatively charged soil surface, or cations could bond with the anionic pesticide resulting in a neutral form. A recent study on the adsorption-desorption properties of penoxsulam narrowed down the possible sorption mechanisms to H-bonding, cation bridging, and surface complexation with transition metals. The data set presented here supports the cation bridging mechanism. As ionic strength of the water treatment was increased, cation concentration increased resulting in the greater likelihood to bridge the anionic form of penoxsulam to the negatively charged soil surface. Figure 1.3 shows no statistical significance between ECw 1.5 dS m-1 and ECw 3.5 dS m-1 , this likely indicates most of the available binding sites of the soil were occupied close to ECw value 1.5 dS m-1 . Due to the similarity in size and ionizable functional group to penoxsulam, it is likely that saflufenacil is undergoing the same phenomena. The water treatments representing different irrigation water quality parameters did have a slight effect on saflufenacil and penoxsulam sorption to soil. The pH treatments indicated that both herbicides likely experience pH-dependent hydrolysis; saflufenacil and penoxsulam showed a decreasing trend in herbicide removal with increasing pH, the opposite of what the hypothesized pH effect would be. This indicates that even if irrigation water has relatively high pH, it is unlikely to substantially change the availability or movement of saflufenacil orpenoxsulam in California orchard soils.

Results from the ECw treatments showed that flushing soil with a solution with moderate ionic strength could help saflufenacil and penoxsulam bind to soil versus low ionic strength. While there were statistically significant differences between water treatments, the overall effect on herbicide dissipation was minimal; the observed difference between the highest and lowest ECw treatment was only about 10% for each herbicide.In the United States almonds are a $6 billion commodity grown solely in California making almonds the second highest grossing commodity in the state behind only dairy products . As of 2020 there were more than 500,000 bearing hectares of almond trees planted in California which produced 1.3 billion kilograms of almonds . Almonds are harvested by mechanically shaking the trees, sweeping the almonds into windrows, and picking the nuts up from the orchard floor. Preharvest herbicide programs and mowing are used to control vegetation that would otherwise reduce harvest efficiency . Glyphosate has been registered in almonds since the early 1990s and glufosinate has been registered since the early 2000s ; these are commonly used herbicides for preharvest orchard preparations because of their broad spectrum weed control and relatively short preharvest interval , three and 14 days, respectively. In 2018, over one million kilograms of glyphosate and nearly 300,000 kilograms of glufosinate-ammonium were applied in almond orchards . Because of the harvesting process, there is ample opportunity for the almond hulls, shells, and kernels to be in close contact with herbicide-treated soil. The majority of California’s almond crop, about two-thirds, drying rack weed is exported and generated more than $4.9 billion in 2019 . Of the exports, 22% were shipped in shell and 78% were shipped shelled . Asia is the largest aggregate market for in shell almonds while the majority of shelled almond shipments go to European markets . Exported shipments of almonds are subject to pesticide residue testing and must be at or below a maximum concentration set by the region’s food safety authority.The maximum residue limit for glyphosate and glufosinate in almonds differ by definition as well as concentration between the European Union and the US. In the United States, both glyphosate and glufosinate MRLs, which are commonly called tolerances, are defined to include the parent compound as well as its primary metabolites .

For clarity these MRLs will be referred to as “total glyphosate” or “total glufosinate” if the concentrations of the metabolites are to be summed with the concentration of the parent compound. The US MRL for glyphosate in almond hulls is 25 mg kg-1 and 1 mg kg-1 for kernels. There is not a separate US MRL for in shell almonds because the residue in inshell almonds is determined by shelling the almonds and measuring the residue in only the kernels. The US MRL for total glufosinate in almond hulls and kernels is 0.5 mg kg-1 . In the European Union, the MRL for glyphosate is 0.1 mg kg-1 in almond kernels . The EU MRL for glufosinate includes its metabolites; the MRL for total glufosinate is 0.1 mg kg-1 . Glyphosate is registered in the EU until 2022 . A recent review completed by the European Food Safety Authority recommended that the MRL for glyphosate be reduced to 0.05 mg kg-1 and an optional total glyphosate MRL for the summation of glyphosate and its primary metabolites, AMPA and N-acetyl-glyphosate, set to 0.2 mg kg-1 . Hence, it is anticipated that in upcoming years glyphosate MRLs will be reduced, and it is a possibility that the chemical may not be re-registered. According to statute, if at any time thesafety of a current MRL is reconsidered, the MRL can be reduced to the lowest limit of analytical detection which is 0.01 mg kg-1 . Because of the importance of the European markets to the California almond industry and the importance of glyphosate and glufosinate to preharvest preparations, lab and field studies were conducted to evaluate the herbicide transfer from soil to almonds during harvest. The objectives were to determine if glyphosate and glufosinate residues can transfer to almonds from soil particles or directly sprayed almonds, whether increasing the PHI could substantially reduce the risk of herbicide in or on almond fractions and quantify the concentration of soil-bound herbicide in almond samples.This experiment was conducted to determine glyphosate transfer from directly-treated almonds to non-treated almonds. This was intended to mimic a situation where a small number of almonds fall to the ground very early and could conceivably be directly sprayed with preharvest treatments and then contaminate the later-harvested crop during harvest and handling steps. Two almonds were directly treated with 0.8325 MBq [14C]-glyphosate by using a microsyringe to dot the stock solution over the entire almond including the inside of the split hull and exposed shell. The two treated almonds were tumbled with nine non-treated almonds using the apparatus and methods described earlier. The almonds were tumbled using a rock tumbler for 15 minutes and let rest for 15 minutes. Before analysis the treated almonds were removed from the bottle, and the untreated almonds were dissected and analyzed for [14C]- glyphosate. This experiment was replicated four times.The whole almonds from each replicate from both soil transfer experiments and the almond-to-almond transfer experiment were separated for three different analyses: whole almond rinse, herbicide adsorption to almond fractions, and a surface swipe after a post-harvest mimicking process. All samples were analyzed using a liquid scintillation counter . The data were corrected for the background levels of radiation in the scintillation counter. The rinsate of whole almonds was used to determine how much [14C]-herbicide was loosely associated with the surface of the almonds. Three whole almonds were rinsed with water using gentle inverted shaking. The rinsate was collected into glass scintillation vials and evaporated using a vacuum evaporation system at 30°C . Once the samples were evaporated to near dryness, 10 mL of Ultima Gold™ was added to each vial. The samples were analyzed using the liquid scintillation counter. To determine how much herbicide was adsorbed to the almond fractions, three almonds were dissected into their hull, shell, and kernel components. Each component was homogenized using a mortar and pestle and liquid nitrogen. Approximately 500 mg of each homogenized almond fraction was collected into a combustion cone and combusted using a sample oxidizer . The combustion product, [14CO2], was collected in 20 mL of scintillation cocktail composed of 10 mL CarboSorb E® and 10 mL Permafluor® . Glass scintillation vials containing the [14C]-samples were analyzed using the liquid scintillation counter. The remaining three almonds went towards a post-harvest mimicking process. The almond hulls were discarded, and the shells were opened by hand cracking through a plastic barrier then discarded. The plastic was swiped using a filter paper and the swipe was added to a glass scintillation vial with 10 mL Ultima Gold™. The swipes were analyzed using the scintillation counter. The kernels were collected, homogenized and combusted, and the combustion product was mixed with scintillant and analyzed using the scintillation counter as described above. The four almond kernels that were tumbled directly in the [14C]- herbicide treated soil were rinsed with 20 mL of water.

To accurately compare emissions of a BE truck with that of a diesel truck, it is important to consider the upstream emissions associated with the fuel cycle in addition to the tailpipe emissions, to capture the emissions associated with generation of the electricity used to charge the BE vehicles. The on-road emissions rates calculated via MOVES and shown in Table 5 were combined with upstream “well-to-pump” fuel cycle emissions from GREET Model. Fuel cycle emissions rates for diesel and electricity production are shown in Table 8. Figure 12 and Figure 13 show the total emissions for both the diesel and BEV options. As expected, the BEV option yields fewer emissions over the vehicle’s lifetime than the ICE option.The economic, business case for BEVs versus diesel trucks in this use-case example is very similar, with the BEV being about half a cent cheaper per mile. However, the break even point is not until the very end of the vehicle’s useful lifetime. If the fleet plans to operate the vehicles for their entire 20-year lifetime on this use-case, then in the long run the BEVs are the better choice. However, there are lots of external factors to consider. Finding locations suitable for installation of private EV chargers will add additional costs for this example, and current operations will need to evolve to accommodate the technology switch. Minor changes of other parameters, such as fuel prices and fuel economy, VMT, interest and discount rate and other financial terms, incentives, pollution taxes, and maintenance costs may be enough to swing the economic comparison in favor of one technology over another. Being able to analyze a wide variety of parameter adjustments, vertical grow racks tailored to a specific scenario, quickly and easily is of high value to fleet managers.

TCOST, the tool discussed in the following section, was designed to enable fleet managers to model their scenario as well as alternative scenarios with adjusted parameters more quickly and easily by removing knowledge barriers while simultaneously leveraging the power of preexisting models utilized in this use-case example.This section will familiarize the reader with the concepts, functions, and data used in TCOST before presenting a sensitivity analysis exploring the effects of parameter adjustments in the context of the use-case example from the previous section to demonstrate how the tool can be used by fleet owners to explore the effectiveness of ICE and BE technology for their business and generate insightful comparative data to make informative decisions about the future purchases of their fleet. TCOST is a parametric spreadsheet-based tool intended to assist fleet managers seeking to quantitatively evaluate the increased costs or savings of opting to acquire BE MHDV units compared to diesel MHDVs projected into the future for the duration of the vehicle’s useful life, assumed to be 20 years. The model uses a series of 21 input variables defined by the user to produce total cost of ownership for a diesel truck versus a BE truck in the same use case. The input page of the spreadsheet model is shown in Figure 14. TCOST is intended to serve a simplified model distilling the functions of several preexisting models into an easy-to-use tool that can help perform electrification analysis and allow users to vary input values to evaluate how each parameter can affect electrification potential in each scenario.

The main outputs of TCOST are comparative total cost of ownership figures broken down by cost category , both as a gross number and on a per-mile basis, as well as a series of visualizations comparing cost breakdowns, break even points, and the expected tailpipe and fuel cycle emissions for both technologies.Maintenance costs for diesel and BE vehicles were taken from AFLEET and California HVIP. Maintenance costs are set to grow by 1% compounded annually by default to reflect the aging and deterioration of vehicle components. Default fuel economy figures for each technology type and vehicle regulatory class are taken from CARB. TCOST uses EIA national average fuel price projections for diesel fuel and commercial electricity. If desired, users can enter their local fuel prices and the tool will project the EIA national trends onto the input starting prices provided by the user and use those in the calculations instead. Table 9 shows the default vehicle parameters in the tool. The model includes parameters for modeling the economic implications of the acquisition of levels 1, 2, and 3 chargers. The purchase prices for each level of charger were based on chargers for sale and listed in CALSTART’s EVSE catalogue . As a caveat, charger installation often comes with additional expenses for utility service upgrades and other necessary investments upstream on the electrical power system. That is, not all fleets can immediately install chargers if the grid conditions are not ready for such installations. These expenses can vary depending on current infrastructure status at the specific location and must be considered independently as part of the decision-making procedure.TCOST calculates WTP and PTW emissions of both technology types to compare the environmental impacts of each option. WTP emissions for diesel fuel were sourced from the “conventional diesel from crude oil for U.S. refineries” fuel pathway within the GREET model.

This fuel pathway includes emissions from the extraction, transportation, refinement, and delivery of the finished diesel fuel product. For electricity, WTP emissions were taken from the “distributed – U.S. mix” pathway in GREET. This includes the generation and transmission of electrical power, including transmission losses, for a national average generation resource portfolio. Future versions of the model will include state-specific or FERC region-specific WTP electricity emissions. PTW energy use and emissions were calculated using per-mile emissions rates by regulatory class calculated using MOVES for diesel vehicles. PTW emissions for BEVs were assumed to be null. The on-road estimates of energy use were multiplied by GREET energy use and emissions rates to estimate upstream emissions and energy use associated with fuel and electricity production. Emissions are reported by TCOST for CO2, VOCs, CO, NOx, CH4, PM10, and PM2.5. Emissions rates are depicted in a table in Appendix A of this report. Upstream vehicle cycle emissions associated with vehicle manufacturing and retirement were excluded in this version of TCOST due to insufficient data coverage for every regulatory class in GREET. In future versions, these will be calculated through a simulated reconstruction of vehicle components in a vehicle-cycle simulation model like Autonomie® to expand the available inventory of vehicle cycle data. Inputs are set by the user and TCOST calculates the corresponding economic comparison of both technology types, reporting lifetime savings and generating four comparative visualizations: cost schedules for the diesel and BE truck , a cost of ownership comparison line graph , and a clustered column chart showing the emissions difference between each technology. Critically, TCOST allows users to override all default parameters with custom values which makes the tool useful for modeling a huge variety of operational and economic scenarios. Users of the tool need only type directly into the input cells to tailor the tool to their fleet conditions and drastically improve model precision for their scenario. Using their conditions as a baseline, they can evaluate the effects of minor parameter changes on cost comparisons between the two technologies.TCOST inputs were set to reflect the conditions described by the use-case example. The example inputs are shown in Appendix B of the report. Where input values were not known, default values were assumed to be reasonable estimates of conditions and were left unchanged. The fuel economy values were taken directly from the results of the MOVES-Matrix simulation and are reflective of the on-road conditions for the use-case. The total cost of ownership reported by TCOST was $630,715.29 for the diesel option and $626,982.88 for the BE option, 4×4 plastic tray resulting in a lifetime savings of $3,732.41 for the BE option with a break even point in the 20th and final year of operational life.

While the BE option costs over twice as much for the initial acquisition of the vehicle, the operation and maintenance costs combined are less than half that of the diesel option over the vehicle lifespan. These cost savings come with the caveat of charger citing and utility upgrade costs, as well as any potential alterations to the drayage operation that might incur additional costs or lost revenue . The visualizations produced by TCOST are shown in Figure 15 through Figure 18. These visuals show the large influence of purchase capital cost and taxes during the first six years of vehicle ownership, and the large difference in on-road operating costs and maintenance costs that show up in the cumulative cost curves across the diesel and BEV alternatives. By comparing these charts, fleet owners and operators can quickly gain insight into the economics and environmental impacts of each potential fleet procurement decision.The use case example presented above for Appalachian Regional Port Drayage results in very small savings that take almost the entire life of the vehicle to realize, compared to some use case examples in the literature that appear to take less than five years to reach payback. Fortunately, TCOST can be customized to specific use cases, allowing fleet owners to easily adjust parameters to identify sub-fleets that make more sense to electrify and to perform sensitivity analysis, helping to assess specific deployment scenario risk and make informed investment decisions. A selection of parameters was adjusted, one at a time, to isolate their effects on the TCO difference between the two technologies. The results of the sensitivity analysis are shown in Figure 19 and are discussed in more detail below. The parameters with the highest sensitivities are BEV purchase price and ICE fuel economy , followed by miles per day, diesel price, and ICE maintenance cost . The sensitivity analysis indicates that a high amount of risk involved in the investment decision, as altering these parameters even slightly can affect total cost savings by over 100%. However, this percentage difference in savings is some when misleading, because the savings were so small to begin with. That is, the high percentage changes observed here do not equate to high absolute values. But, the model sensitivity analysis does indicate that assumed future conditions does have a large impact on the simulation.Because diesel fuel economy won’t change very much over time, due to the consistent on-road conditions of the vocation, the most critical parameter in play is the purchase prices of the BEVs. If there are any incentives available to the fleet for investing in BE trucks, a simple reduction of purchase price by only 1% would almost double expected savings under these conditions. Much recent regulatory focus has been on monetary incentives for BE technology because purchase price represents the largest expense occurred by an electrifying fleet. Fuel prices are notoriously hard to project. If diesel becomes more expensive in the long-term, it would improve the savings of BE investments. Even if diesel fuel prices in the operational area are notably higher than the national average used in TCOST, it would have a large impact on savings. If the fleet is expected to travel more daily miles in the future, additional miles travelled would also have significant impact on the fleet’s savings . Finally, under a diesel option, if future retrofits are required to keep the vehicle and fleet compliant with evolving emissions standards, diesel maintenance costs might increase, positively impacting fleet savings under the BE option. TCOST enables fleet managers to quickly and accurately adjust parameters to model a variety of possible scenarios to produce sensitivity analyses like this. TCOST customizability and parametric design allow the tool to quickly model case-specific conditions or a variety of alternative futures. Its spreadsheet-based nature is accessible, reducing modeling knowledge and information barriers, and allowing fleets of all shapes and sizes to gather data to make informed decisions about the futures of their fleets.Fruit trees should be planted where they will receive full sun for 6 or more hours per day during the growing season. For maximum production, fruit trees need soil that is deep and well drained. Such soils do not occur everywhere in California, especially in residential areas where the topsoil may have been partially removed by land grading and the remaining soil has been compacted by the weight of construction machinery.

Perennial weeds are usually most susceptible to glyphosate in the bud stage of growth immediately prior to flowering and in the fall when weed foliage is still green. Both stages represent times when weeds are translocating most of their photosynthates from leaves to roots. Since glyphosate primarily moves in the same direction as sugar in phloem tissues, glyphosate translocation to perennial roots is maximized when applied at these timings. It is also important to consider the stage of growth and age of the crop prior to using glyphosate. In woody perennial crops, most glyphosate formulations can be safely applied as a directed spray to the base of dormant plants. Use extreme care on smooth-barked crops, however, as certain formulations or surfactants may allow glyphosate to be absorbed through the bark, resulting in injury or death of treated crop plants. Shielded nozzles and low sprayer pressure may aid in preventing accidental glyphosate application or drift to crop plants, whether dormant or not.Glyphosate is a broad-spectrum foliar herbicide that, when applied at the proper rate, is able to control emerged annual, biennial, and perennial broadleaf and grass weeds. It is available in a wide variety of formulations and from multiple manufacturers, so most growers have ready access to glyphosate to use in their farming operations. To get the most consistent weed control with this herbicide, adjuvants should be added to the spray mixture as necessary. Target weeds should be inspected to determine whether they are actively growing or are species best controlled at a different stage of growth. Physically damaged weeds or weeds that are stressed by drought or excess water may not be fully controlled. Foliage should be clean and dry at the time of application, pot growing systems and environmental conditions should be favorable for herbicide application and optimal uptake into the plant.

Mixtures or sequential application of glyphosate with other herbicides may enhance control of difficult weed species and potentially delay onset of herbicide resistance in the weed population. If these factors are considered and any necessary corrective actions taken prior to application, glyphosate can remain a very effective herbicide for years to come.Allelopathy, the production of chemicals by a plant species that might influence nearby plants or soil microbes, is an important functional characteristic that can change neighbor plant performance and eventually plant structure and function. The allelopathy phenomenon was identified for the first time in the late 1930s by Hans Molisch as the influence of one plant on another through the release of chemicals into the environment . It was further characterized as any direct or indirect harmful or helpful influence of one plant on another through the synthesis of chemical substances that are released into the environment . Allelopathy significantly influences the spread of invasive plants, acting as a key factor for species like Hirschfeldia incana to dominate new territories. These invasive plants release chemicals that inhibit the growth of surrounding native flora, thereby gaining an upper hand in these environments. This chemical interaction not only affects individual species but also extends its impact to whole ecosystems. Invasive species can change the composition of native plant communities, disrupting local food chains and nutrient cycles. Moreover, allelopathic activities can lead to drastic changes in soil microbial populations, affecting soil quality and nutrient dynamics.

These alterations can create a self-reinforcing cycle, further solidifying the presence of invasive species and complicating restoration efforts. A thorough understanding of allelopathic relationships in plant invasions is crucial for effective ecological conservation and for anticipating the long-term effects of invasive species on biodiversity and ecosystem functions.The application of allelopathy in agriculture is emerging as a sustainable alternative to traditional weed control methods. Utilizing allelopathic plants or their by-products can naturally curb weed growth, diminishing the dependence on chemical herbicides. This method aligns with ecofriendly farming practices and aids in maintaining ecological balance and soil integrity. For example, incorporating allelopathic cover crops into crop rotations can manage weeds effectively while improving soil fertility. Identifying specific allelochemicals and understanding how they work could lead to new, environmentally safe herbicides. However, leveraging allelopathy in agricultural settings requires careful evaluation of its effects on non-target species and the overall environmental impact. Research in this domain is poised to offer key insights into the best combinations and sequences of crops for efficient weed control, contributing to more sustainable and ecologically conscious farming methods. Invasive species adopt a wide array of strategies to establish in new habitats. Among these qualities is the capacity to create allelopathic compounds that can directly restrict neighboring native plants or indirectly depress native plants via disruption of beneficial below ground microbial mutualisms or changed soil resources. Allelopathy is most likely to be associated with non-native plant invasion, which means that most invasive species spread faster because of their allelopathy. Allelopathy has become well-known in the field of invasion biology as one of the possible weapon traits in the novel weapon hypothesis because of these potential negative impacts on neighbor plant fitness .

The physiology and rate of population development of native species are known to be altered by non-native invaders, as are the abundance of species within a community and even the stable states of entire ecosystems . Although there are obvious negative effects on specific plant species and their communities, it is unclear how important allelopathy is as a characteristic of many invaders as opposed to a few well-studied examples. In other words, the degree to which allelopathy is a key characteristic in the toolkit that boosts the success of exotic invasions is still unknown. Brassica plants, including species like cabbages, broccoli, cauliflower, kale, and Brussels sprouts, contain allelochemical compounds like glucosinolates. These compounds, under exceptional conditions, can be released into the environment and have been observed to affect seed germination and plant growth . Hirschfeldia incana, commonly known as short pod mustard, is closely related to the Brassica genus and belongs to the Brassicaceae family, often referred to as the mustard family. This family includes a wide range of well-known vegetables and oilseed plants. The relationship between Hirschfeldia incana and Brassica species is characterized by their genetic, morphological, and ecological similarities. These similarities include the production of glucosinolates , four-petaled flowers arranged in a cross shape, and seed pods known as siliques. The taxonomy of the Brassicaceae family is complex and subject to revisions as new genetic information becomes available. The close relationship between Hirschfeldia incana and Brassica species is not only evident in their physical appearance but also supported by molecular studies that examine DNA sequences to understand their evolutionary relationships.Furthermore, Hirschfeldia incana’s ability to thrive in disturbed soils and its widespread distribution as a weed can provide valuable insights into adaptability and ecological strategies shared with some Brassica species. These Brassica species are known for their capacity to grow in various environmental conditions. Understanding these relationships has significant implications for agriculture and horticulture, planting racks as it can aid in the development of more resilient crop varieties. This research has many benefits, one of them is being able to Identify another plant species that has the potential to suppress the growth of an invasive species.. Also over the course of time researchers might discover a native plant that might inhibit the growth of the invasive species. It can also open some for scientists ideas like how to control allelopathy. Also it would show us if there is a significant characteristic that both plants share. In this research, we delve into the sample collection and preparation methods employed for shortpod mustard, a species with potential allelopathic properties, and provide insights into how similar procedures can be adapted for studying sunflowers . These distinct plant species offer valuable insights into the world of plant ecology, allelopathy, and ecological interactions, shedding light on the intricate relationships that exist within ecosystems. The main goal of the study was to see how the liquid from shortpod mustard leaves affects the growth of sunflower seeds. We did this by comparing how many seeds sprouted in two different petri dishes. One dish had plain water , and the other had the mustard leaf liquid. By looking at the differences in how many seeds grew in each dish, we could understand the effect of the mustard leaves on the sunflower seeds.Shortpod mustard and sunflower are two plant species that have captured the attention of ecologists and botanists alike due to their distinct characteristics and significant ecological roles. Each of these plants possesses unique traits and ecological significance, making them compelling subjects of study in the realm of plant science.

Hirschfeldia incana, commonly known as shortpod mustard, is a remarkably resilient plant species with allelopathic properties that have piqued the interest of researchers. This member of the Brassicaceae family thrives in a variety of environments, including disturbed ecosystems like roadside verges, agricultural fields, and other areas with disrupted natural habitats. What sets shortpod mustard apart is its ability to release biochemical compounds into its surroundings, thus potentially influencing the growth and development of neighboring plants. Understanding the allelopathic interactions of shortpod mustard, as well as the chemical constituents responsible for these effects, holds profound ecological importance. This knowledge can shed light on its ecological impact and uncover potential applications in areas such as weed management and sustainable agriculture. On the other hand, Helianthus annuus, known as the common sunflower, boasts its own distinctive characteristics and ecological significance. Belonging to the Asteraceae family, sunflowers are easily recognizable by their vibrant yellow flowers and towering stalks, making them iconic in the botanical world. Beyond their aesthetic appeal, sunflowers serve multiple practical purposes, including the production of edible seeds and oil. However, their ecological role extends beyond human consumption. Sunflowers are renowned for their competitive growth and allelopathic potential, which can influence neighboring plant species and ecosystem dynamics. Thus, delving into the study of sunflowers offers valuable insights into their ecological interactions, growth patterns, and potential impacts on surrounding vegetation. In essence, shortpod mustard and sunflower, with their contrasting yet complementary attributes, form a captivating duo for ecological research. By unraveling the mysteries of their allelopathic interactions and biochemical constituents, we gain a deeper understanding of their roles in the natural world and unlock potential applications that can benefit both science and society.Mature shortpod mustard leaves, known for their potential allelopathic properties, were collected during the early morning hours from the vicinity of Crest Plaza Riverside. Following the collection, to preserve the leaves, we used a freeze-drying method right after collection. This method, called freeze-drying or lyophilization, involved freezing the leaves at very low temperatures and reducing the pressure around them. Once the freeze-drying was done, we roughly split the dried leaves into 8 Eppendorf tubes and weighed the samples. The total weight of dried leaf tissue was 0.69 grams.To initiate the extraction process, a combination of disruption beads and bead silica mobile was added to each sample. Then the samples were homogenized at a consistent speed of 1800 rpm for a precise duration of one minute. This was followed by the addition of a calculated 5.5 ml of water, distributed evenly across the 8 tubes . These samples were mixed vigorously. Once done, these samples were incubated on a calibrated heating block at 25°C for a 24-hour cycle, promoting maximum extraction. Following the incubation, a brief centrifugation process at high speed was applied for 10 seconds. The centrifuge was used to separate the heavier parts from the liquid. After this process, the clear liquid was carefully moved into a single 15 ml tube, and more water was added to bring the total volume up to 6.9 mL . The leachate, now at a 1:10 dilution , was ultimately stored in the larger tube and refrigerated for stability, ready for the next phase of the experimental procedure involving seed germination tests.From each of these populations, a subset of 14 seeds was chosen. Prior to any treatment, it was of paramount importance to ensure the seeds were free from contaminants and in prime condition for the experiment. To this end, they were subjected to a sterilization regimen which began with a brief 10-second immersion in 70% ethanol. Following this, the seeds were washed twice in sterile water to rid them of any residual ethanol.