The effect of zero tillage is dependent on climate, especially on rainfall, and the effect is more pronounced in drier areas . The energy requirements of zero tillage and reduced tillage are less, so GHG emissions are lower . GHG emissions were reduced by 1.5 Mg CO2-e ha 1 year 1 in zero tillage-based wheat and maize systems .Crop residue return has positive impacts on SOC, however, its effectiveness varies with tillage practices . Retaining residues on the soil surface increases the soil C sequestration , whereas residue incorporation with inversion tillage may lead to higher N2O and CH4 emissions . Amount of residue return is positively related to the C sequestration . Residue return with optimum fertilizer input, paddy-upland rotation, improved crop cultivars, and use of legumes in rotation are some of the improved management practices for enhancing amounts of crop residue return to the soil . Crop retention can reduce the requirement of fertilizer and therefore, may limit the GHG emission. The application of bio-char to soil has the potential to offset 12% of global GHG emissions, as it can stabilize decaying organic matter and associated CO2 release, and can remain in soil for hundreds or even thousands of years . The retention over longer period is due to reduction in mineralization rate by 10–100 times from that of crop biomass . A meta-analysis reported that bio-char can either increase or decrease soil C depending on the types of bio-char/soil and duration . In addition to its effect on SOC, bio-char application may decrease soil N2O emissions to an extent of 9–12% or even 50% .Improved water management enhances C sequestration by increasing NPP and the subsequent addition of biomass to soil . It is estimated that improved water management could mitigate 1.14 t CO2-e ha 1 year 1 of GHG emissions .
In dryland agricultural system, drying weed crop productivity and the above- and below-ground inputs of C to the soil can be improved through efficient water management practices which enhances the plant-available water . However, drip irrigation with frequent wetting-drying cycles may promote soil CO2 emission through greater microbial activities . Micro-irrigation/fertigation also reduces N losses and hence lower GWP . In rice cultivation, soil flooding is known to emit a large amount of CH4 , which can significantly be reduced from improved water management such as alternate wetting and drying , also called intermittent flooding . However, the intermittent flooding may result in higher N2O emission , which necessitates water management to be in synchrony with inorganic fertilizer and organic matter inputs. Reduced water application reduces the C footprint of pumping water .The application of N fertilizer from the right source, at the right dose, right time, and in the right place enhances crop yield, N use efficiency, and SOC storage, and mitigates GHG emissions . Optimum and balanced doses of nutrients maximize crop yields, resulting in relatively more C inputs from both above- and below-ground plant biomass to the soil. Nitrogen can be applied effectively by correlating the leaf greenness with the leaf N content, and this can be done with a chlorophyll meter, leaf color chart, or optical sensors . Decision support systems like Nutrient Expert and Crop Manager are becoming popular for efficient nutrient management . ‘Nutrient Expert’-based management reduced on average 13% of GHG emissions from rice, wheat, and maize compared with farmers’ fertilizer practices. Studies conducted by Gaihre et al. reported that in Bangladesh, the deep placement of urea in a rice-rice cropping system reduced N loss as N2O and improved the crop yield. Thus, deep placement of urea can mitigate global warming and improve SOC by producing more biomass than traditionally applied urea. Enhanced fertility management can improve SOC content at the rate of 0.05–0.15 Mg ha 1 year 1 . In a meta-analysis conducted by Ladha et al. , it was reported that N fertilization promotes SOC storage in agricultural soils throughout the world. Benbi and Brar reported that the application of balanced fertilization positively impacted the soil C sequestration due to its effects on crop growth.
Balanced fertilization improved SOC concentration in rice-wheat and maize-wheat cropping systems because of the greater C input associated with enhanced primary production and crop residues returned to the soil . To improve soil health and soil productivity through balanced fertilization, the Government of India has started a “Soil Health Management ” program under the National Mission for Sustainable Agriculture . In India, the Soil Health Card has been useful in assessing the status of soil health, and when used over time. The SHM program aims to promote Integrated Nutrient Management through the judicious use of chemical fertilizers including secondary- and micro-nutrients in conjunction with organic manures and bio-fertilizers. The SHC-based recommendations have shown an 8–10% reduction of chemical fertilizer use with a 5–6% increase in crop yields .In India, the availability of manure as a source of nutrients and C in agricultural practice reduced from 70% of the total manure produced in the early 1970s to 30% in the early 1990s . Three hundred and thirty-five Mt of dung is produced per annum in India, out of which 225 Mt is available for agricultural use . This is only one third of the FYM requirement of the country that is needed to achieve the full C sequestration potential . Use of organic manure such as compost can enhance soil C stocks but may also result in higher CO2 emissions . Application of organic manure can improve SOM by supplying enzyme-producing microorganisms with C and N substrates , thus enhancing the structure and diversity of the microbial community . However, application of inorganic nutrients with FYM sequestered C at the rate of 0.33 Mg of C ha 1 yr 1 compared to 0.16 Mg of C ha 1 yr 1 in NPK application alone . Even in a hot, semi-arid climate, balanced and integrated nutrient management along with FYM could increase SOC in soil . Regmi et al. , in a long-term study, reported the accumulation of soil C in a triple-cereal cropping system with organic amendment. In a rice-wheat cropping system, compared to NPK, the use of organic material increased SOC ranging from 18 to 62% . Likewise, Duxbury reported SOC accumulation from 0.08 to 0.98 Mg C ha 1 yr 1 in rice-wheat cropping systems through addition of FYM in India and Nepal. Several researchers have reported higher GHG fluxes in different types of soil when manures were added .
In a soybean-wheat cropping systems with an organic amendment, Lenka et al. reported increases in SOC stocks and N2O and CO2 emissions but the annual GWP was lower.Deep-rooted crops and crop varieties can sequester more CO2 in lower soil profiles . Growing deep-rooted crops also reduces nitrate leaching to the groundwater and thereby reduces N2O emission , curing weed improves SOC stocks, and extracts nutrients and moisture from deeper soil layers . Deep-rooted perennial crops could also significantly decrease the requirement for tillage . Plants with improved root architecture can improve soil structure , hydrology , drought tolerance , and N use efficiency . Van de Broek et al. compared the amount of assimilated C that was transferred below ground and potentially stabilized in the soil from old and new wheat varieties. The authors reported that old wheat cultivars with higher root biomass transferred more assimilated C down the soil profile over more recent cultivars. Recently, Dijkstra et al. proposed a new ‘Rhizo-Engine framework’ emphasizing a holistic approach for studying plant root effects on SOC sequestration and the sensitivity of SOC stocks to climate and land-use changes. Mycorrhizal association is another important trait that could play a crucial role in moving C into soil through active participation with plants. It is reported that plants with mycorrhizal associations can transfer up to 15% more C to soil than their non-mycorrhizal counterparts . The most common mycorrhizal fungi are marked by thread-like filaments, hyphae that extend the reach of a plant, increasing its access to nutrients and water. These hyphae are coated with a sticky substance called glomalin which are known to improve soil structure and C storage. Glomalin helps the organic matter bind with silt, sand, and clay particles, and it contains 30–40% C and helps in forming soil aggregates . Averill et al. using global data sets, observed 70% more C per unit N in soil dominated by ectomycorrhizal and ericoid mycorrhizal-associated plants than arbuscular mycorrhizal-associated plants. Another recent synthesis by Verbruggen et al. opined that the mycorrhizal fungi can increase C sequestration through “enhanced weathering” of silicate rocks through intense interactions.The excessive use of pesticides in crop production has amplified to fight against insect pests and diseases. While the use of pesticides captures more C from improved crop production, it also increases GHG emissions from the processes involved in the use of synthetic pesticides . Integrated pest management can reduce pesticide use and increase crop yields. A study conducted in 24 countries of Asia and Africa has shown that the use of IPM to control pests can increase crop yields by more than 40%, and can reduce pesticide use by 31% . Research has shown that any pest management practices that lessen foliar spraying are able to reduce GHG emissions . CSPM is proposed by the FAO , and its aim are to reduce crop losses due to pests, improve ecosystem services, reduce GHG emissions, and make the agricultural system more resilient .A cover crop used to cover the ground surface during the fallow period prevents nutrients leaching from the soil profile, and provides nutrients to the main crops . Poeplau and Don reported a reduction in SOC loss by cover cropping. A significant area in South Asia, where cultivation of a single crop is the practice, provides an opportunity for cover cropping. Likewise, in intensive double-cropping areas, a short-duration cover crop such as sesbania can be grown to improve soil fertility including soil C . In a meta-analysis, Poeplau and Don estimated that using cover crops in 25% of the world’s farmland could offset 8% of GHG emissions from agriculture. Cover cropping has also been reported to reduce N2O emissions . Aryal et al. reported that cover crops and fallow rotation in warm and moist climates can reduce a net loss of 0.98 Mg C ha 1 in 7-year period. Creating borders of permanent vegetation along the edges of the field is another way to provide continuing live cover for agricultural soils . The possible effect of no-till in increasing SOC is more prominent when cover cropping is included in the system . Cheng et al. and Dignac et al. reported improvement in SOC stocks through rhizodeposition and root litter addition, which is greater with perennial crops than with annuals. In a policy analysis report on soil health and C sequestration in US croplands, Biardeau et al. reported that agroforestry, in which crop cultivation is intermixed with growing trees and sometimes with grazing livestock, has the highest potential to hold C, ranging from 4.3 to 6.3 MT CO2-e per ha annually.Inclusion of a dual- or multi-purpose legume in a rotation is likely to balance the organic and inorganic fertilizer inputs and its effect on SOC stocks . In South Asia, several researchers have shown similar benefits at the system level of optimizing crop rotations in CA mode in rice-wheat and rice-rice rotations . Legumes with the ability to fix atmospheric N benefit subsequent crops by increasing biomass production, crop residue inputs, and subsequently the total SOC in legume-cereal crop rotations . Reducing overgrazing ; balancing SOM decomposition through manures, crop residues and litter; and enhancing the mean annual NPP, are known to improve SOC in agricultural soils . Greater SOC stocks and more stabilized SOC can be obtained by increasing soil biodiversity . Havlin et al. reported that instead of continuous soybean cultivation, the inclusion of grain sorghum in a rotation increased soil organic C and N and that growing high residue crops along with reduced tillage could increase productivity. Ladha et al. reported that in different parts of the Indo-Gangetic Plains, the implementation of CA along with intensive crop diversification resulted in a 54% increase in grain energy yield, with 104% more economic returns, a 35% reduction in total water input, and a 43% lower global warming potential intensity compared to farmers’ conventional management practices. Improved agronomic practices can lead to SOC changes which are often higher than the proposed 0.4% .