Keywords

1 Introduction

Soils constitute the largest carbon (C) pool in the terrestrial ecosystem, and its stock in various organic forms varied from ~1500–2000 Pg (1 Pg = 1015 g) C upto a depth of 100 cm. Presently, worldwide C sink for the terrestrial regions is projected to include ~550–700 Pg C in vegetation and ~ 1200–1600 Pg C in total C (organic + inorganic) upto a depth of 100 cm (Paustian et al. 1997a). However, according to Eswaran et al. (2000), soil upto a depth of 100 cm may constitute ~2500 Pg of total C (organic + inorganic). Generally, C is divided into five major pools per Intergovernmental Panel on Climate Change (IPCC 2007), namely, oceanic (~38,000 Pg), geologic (~5000 Pg), pedologic (~2460 Pg), soil organic C (SOC; ~950 Pg), and atmospheric (~800 Pg). There is a globally growing concern on soil C sequestration through crop production and soil management practices (Russell et al. 2005; Wilson and Kaisi 2008; Singh and Benbi 2018a, b) not only to enhance soil C storage and to mitigate global greenhouse gases (GHGs) emission (Singh and Benbi 2020a, b) but also to improve soil health for long-term sustainability of a crop production system. Soil C sequestration is a technique in which atmospheric C is sequestered into the soil by improved technologies, which improved the soil health and yield potentials (Sundermeier et al. 2008). The oxidation of soil organic matter (SOM) in cultivated agricultural soils has been estimated to contribute ~50 Pg C to the atmosphere (Paustian et al. 2000). During the last decade, the carbon dioxide (CO2) concentration in the atmosphere has increased by ~85 ppm (Raich and Potter 1995). For this, agriculture sector has been considered as major culprit as a sector contributed ~one-fourth of the historic anthropogenic CO2 emissions during the past two centuries. On a global scale, agriculture sector has the potential to offset GHGs emission by 1.15–3.30 Pg C year−1 (Cole et al. 1997). Therefore, soil C sequestration by terrestrial vegetation has been the promising approach for mitigation of GHGs (Cole et al. 1997), as the terrestrial system associated with the soil and crop management has been the key player in global C budget (Lal 2004a). Bowen and Rovira (1999) reported that the buildup of 1.0 t SOM in soil removes 3.667 t CO2 from the atmosphere. Schlesinger (1997) has reported that >2/3rd of organic C storage in the terrestrial ecosystem occurred in SOM with a net C flux of ~60 Pg C year−1 from the soil to the atmosphere.

Among the best agricultural management practices, tillage frequency (Campbell et al. 1995; Six et al. 2004; Calegari et al. 2008; Lopez-Garrido et al. 2009; Anikwe 2010), tillage depth (Jitareanu et al. 2009), type of tillage implements (Dong et al. 2008; Patra et al. 2010), nutrient management (Kaur et al. 2008; Banger et al. 2010; Singh and Benbi 2018a; Singh et al. 2021a), organic manure application (Raji and Ogunwole 2006; Singh and Benbi 2018a), crop residue incorporation (Wang et al. 2010b; Sharma et al. 2020a), green manuring of soil (Yadvinder-Singh et al. 2004; Ghosh et al. 2010), land use change (Singh and Singh 2017), land use cover (Benbi et al. 2015; Singh and Benbi 2018b), crop cover (Entz et al. 2002; Wang et al. 2010b), cropping intensity (Campbell et al. 2007; Singh and Benbi 2020a, b), cropping sequence/rotation (Campbell et al. 1995; West and Post 2002; Wilson and Kaisi 2008; Singh and Benbi 2020a, b), alley cropping (Okonkwo et al. 2009), and irrigation water management (Minamikawa and Sakai 2007) are important that contribute significantly toward soil C sequestration and consequent mitigation of GHGs emissions. Optimum management of row crop field coupled with reduced soil tillage, efficient nutrient management, and water conservation are the credible management practices that hold good promise as a means of soil C sequestration, although the photosynthetic CO2 assimilation rates vary largely depending upon climatic conditions, soil fertility, and other soil and plant factors (Lal 2004b; Sharma et al. 2021a).

Soil C sequestration contributes significantly toward soil tilth (Lal et al. 1997), fertility (Sainju et al. 2008), water holding capacity (Singh and Benbi 2016), and ultimately leads to improvement in crop yield (Singh and Benbi 2018a; Sharma et al. 2020a). Widespread adoption of recommended crop production practices in the United States (U.S.) has the potential to sequester ~45–98 Tg (1 Tg = 1018 g) SOC in croplands (Lal 2003). It had a special significance for tropical and subtropical ecosystems, where the soils are inherently low in SOC, and the production systems are low in soil fertility owing to greater oxidation of SOM under high temperature conditions. The Council for Agricultural Science and Technology (CAST) suggested that adoption of improved agricultural practices in croplands can enhance C sequestration rates from 0.1 to 1.0 Mg ha−1 year−1, although the assimilation rate decreased as soil approaches a steady equilibrium state (CAST 2004).

Soils do have the capacity to sequester atmospheric C that varied with the soil texture, quantity of organic inputs, and the initial SOC status (Ingram and Fernades 2001; Paustian et al. 2000; Singh and Benbi 2021). Soil organic C in swell-shrink soils in subhumid tropics attains quasi-equilibrium values between 5 and 30 years depending upon soil texture and native vegetation (Naitam and Bhattacharyya 2004). Soil management practices have the prospective to contribute greatly toward soil C sequestration since the C sink capacity of the world’s agricultural and degraded soils is ~50–66% of historic C loss (~42–72 Pg) (Lal 2004b; Bangroo et al. 2011). The global historic losses of soil C due to intensive cultivation have been estimated to be around 25% (~55 Pg C) of original C in virgin and uncultivated soils (Cole et al. 1997). Soil organic C acts as a simultaneous source and sink for essential plant nutrients (Campbell et al. 1995; Bationo et al. 2007) and plays a vital role in maintaining soil fertility and productivity (Bronson et al. 2004) by improving the physical and chemical characteristics of soils (Lal et al. 1997). Crop production and soil management practices for C sequestration simultaneously improved the organic matter inputs to soil and decreased the loss of soil organic matter through decomposition (Sharma et al. 2020a). Nonetheless, the practices leading to increased soil C sequestration are both site and situation specific (Paustian et al. 1997a; Koul and Panwar 2008; Singh et al. 2020a), which inter alia depend on environmental and socioeconomic factors affecting soil C dynamics. Recent global estimates have revealed that the capacity of agricultural soils to sequester ~20–30 Pg C over the next 50–100 years (Paustian et al. 1997a). Soil C sequestration is necessary not only to enhance soil C storage for C trading and to mitigate GHG emission but also to enhance the farmer’s livelihoods (Sainju et al. 2008).

Conventional rice–wheat cropping system in the entire Indo-Gangetic Plains (IGPs) depends much on the fertilizer–N application, but its higher doses lead to serious environmental implications, namely, emission of GHGs and underground water pollution (Bhatt et al. 2021). The lack of proper crop rotations with legumes, intensive tillage, open-field burning of rice residues, overexploitation of groundwater and overfertilization, malnutrition, biodiversity loss, and so on is considered as major reasons for the deterioration of soil health and sustainability of a rice–wheat cropping system (Sharma et al. 2021b). The faulty irrigation practices, namely, flood irrigation, as well as crop establishment methods such as intensive tilling in rice–wheat cropping systems, is considered responsible for large-scale C equivalent emissions (Singh et al. 2020a). Crop residue burning has been the most threatening sustainability issues in the IGPs, particularly under rice-based cropping systems affecting the environmental sustainability due to reduced C sustainability. Therefore, to sequester C back in soil for a longer period of time or to hinder C gases emitted to the atmosphere, researchers across the country invented, tested, and recommended a large number of techniques for producing more using less land, energy, or water after reducing the C footprints. In view of highly variable crop production and soil management practices in crop production (Singh et al. 2019a, b; Singh and Benbi 2020a, b; Sharma et al. 2020b), an attempt was made to gather information pertaining to C sequestration potential and dynamics of soil C associated with best crop production and soil management practices.

2 Soil Organic C in Different Soil Types

The SOC concentration in Indian soils ranges from 2.1 to14.8 g kg−1, with a mean value typically <0.5%. The loss of C from historic levels due to higher C footprints urgently needs diligent attention to cut down C losses and increased organic C concentration to the desired levels 0.5% to 1.0% (Swarup et al. 2000). India has great diversity of soil types, namely, Alfisols (~81 Mha), Vertisols (~60.4 Mha), Inceptisols (~51.7 Mha), Ultisols (~36.6 Mha), Entisols (~24.8 Mha), Aridisols (~18.3 Mha), Mollisols (~1.8 Mha), and Gelisols (~0.8 Mha) (Velayutham et al. 2000). Soil organic C pool in different soil orders in India and the world.

3 Crop Production and Soil Management Practices for Increased C Sequestering

3.1 Conservation Tillage and C Sequestration

Tillage management has been the most credible option capable of mitigating CO2 emissions due to its role in preventing organic matter oxidation (Singh et al. 2020a, b). Tillage accentuates soil organic matter disintegration processes through the physical disturbance by breaking bigger aggregates into the smaller ones (Benbi et al. 2016), which reduces the emission of CO2 gas (Oades 1984; Beare et al. 1994). Tillage also affects soil temperature, aeration, and water relation by its impacts on surface residue cover and soil structure (Paustian et al. 1997b). Reducing tillage intensity with stubble mulching helps in improving the C sequestration and hence the organic matter content of soils (Hu et al. 2010; Sainju et al. 2010) through C accumulation (Garcia-Franco et al. 2015). In a rice–wheat cropping system, the conventional tillage (CT) coupled with open field residue burning prior to wheat establishment has high C footprints and low C sustainability (Singh et al. 2020a; Singh et al. 2021b). They have reported that compared to the CT, rice residue retention with happy seeder technology for wheat establishment leads to a significant reduction of C and energy footprints by 14.1% and 12.9%, respectively, which is a must for sustainable agriculture in the region (Fig. 1) (Singh et al. 2020a).

Fig. 1
figure 1

Influence of tillage intensity for rice residue management and wheat sowing on carbon sustainability index (Acronyms: HS-happy seeder, ZT-zero tillage, RT-rotavator tillage, MBP-mold board plough tillage, and CT-conventional tillage (Source: Singh et al. 2020a)

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Liu et al. (2016) revealed significantly higher microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) concentrations in surface soil layers than in the subsurface layers which further linked with lesser labile C and N pools as the soil becomes deeper and deeper. Similar reports have already been reported by researchers under different ecosystems, namely, forestland (Agnelli et al. 2004), grassland (Fierer et al. 2003), and arable land (Taylor et al. 2002). The MBC concentration accounted for 6.79%, 3.90%, 2.84%, and 2.24% of the SOC concentration, while MBN concentration accounted for 3.13%, 3.09%, 2.29%, and 1.55% of TN concentration under grassland, forest, plough tillage (PT), and no-tillage (NT), respectively. At the 5–15 cm depth, the MBC:MBN ratio was higher under grassland and forestland than cultivation practices. At the 15–25 cm depth, the MBC–MBN ratios were generally lower under PT and NT than grassland and forestland. The MBC concentration accounted for 4.94%, 3.20%, 2.45%, and 1.50% of SOC concentration, while MBN concentration accounted for 2.44%, 1.75%, 1.74%, and 1.78% of TN concentration under grassland, forestland, PT, and NT, respectively. The ratio of MBC–MBN is generally not affected by variation in soil depths under different land-use systems. Under zero tillage crop establishment systems, MBC:MBN ratios significantly decreased with the increase in soil depth. However, retention of crop residues further promoted the soil health indicators and reduced the soil bulk density thus enhancing other soil properties.

Reduced tillage instead of intensive or zero tillage (ZT) is a win–win strategy for promoting C sequestration sustainably (Sainju et al. 2010; Garcia-Franco et al. 2015) through C accumulation within the small macroaggregates and microaggregates at the 5- to 15-cm depth (Garcia-Franco et al. 2015). Reduced tillage is considered important to promote the formation of new aggregates and soil C within them and therefore improved the soil properties because of enhanced SOC (Sainju et al. 2010). The soil management options that contribute to reduced decomposition or soil respiration, vis-à-vis reduced tillage or NT practices, mulch farming, and reducing bare fallow or increased cropping intensity, lead to C sequestration in soil (Halvorson et al. 2002). The adoption of appropriate tillage practices has received worldwide attention owing to the high C sequestration potential (Singh et al. 2020a). Campbell et al. (1995) reported that continuous wheat (Triticum aestivum L.) cultivation under NT system gained ~1.5 t ha−1 more C than continuous wheat in conventional tillage (CT) plots in comparison to NT sown fallow–wheat that gained ~0.5 t ha−1 more C than fallow–wheat in CT plots. An increase in SOC content with decreased fallow frequency in a cropping sequence shows the effect of added crop biomass (aerial and underground) and reduced soil disturbance during tillage operation (Campbell et al. 1995). The underground crop biomass has been reported to boost SOC buildup to a greater extent than aerial biomass, as the crop roots have a significant effect on SOC content (Kaisi and Grote 2007) because ~40% of the photosynthates synthesized in different plant parts are released in the rhizosphere through plant roots within an hour of their production (Kumar et al. 2006). Such an increase in SOC content with root biomass can be explained by the exudation of organic compounds that bind soil particles and stabilizes SOC (Chevallier et al. 2004). On the contrary, however, Halvorson and Reule (1999) reported that C sequestration efficiency, when measured on the basis of C in aerial biomass, was increased by ~30% compared to only ~11% when estimated by considering C in both aerial + root biomass with the application of N over no-N plots.

The accumulation of SOC to a greater extent in the surface layer might be attributed to the accumulation of crop residue in the top layer, and even the root biomass grows abundantly in the top soil layer (Kaisi and Grote 2007; Sharma et al. 2020a). Wright et al. (2007) reported the most influential effect of tillage on SOC restoration at 0–5 cm soil depth and extended impact to the 15–30 cm depth for wheat (Triticum aestivum) and sorghum (Sorghum bicolor L.). Wright and Hons (2005) reported significantly higher soil C sequestration in NT than CT treatment imposition under sorghum–wheat–soybean cropping sequence at 0–5 cm soil depth. In a Rhodic Hapludox of Southern Brazil, NT resulted in 6.84 Mg C ha−1 in the upper (0–10.0 cm) soil layer, which represents ~64.6% high C than CT under various winter crop cover treatments (Calegari et al. 2008). Upto ~20–40% loss of SOM is reported to occur after shifting the land for agricultural production from original untilled conditions (Davidson and Ackerman 1993). Over and above, the role of tillage management on soil C sequestration is considered time-dependent (Six et al. 2004). In humid and dry temperate climates of the United States, Six et al. (2004) reported that newly converted NT cropping systems rather increase net global warming potential (GWP) relative to CT practices. However, more than 10-year long-term adoption of CT practice in humid climatic conditions leads to a significant reduction in GWP. In comparison, >20-year long-term adoption of NT practice is required under dry climatic conditions for reducing GWP and that too with a high degree of uncertainty (Six et al. 2004). In Mollisols of Argentina, SOC in the upper 7.5 cm layer of degraded soils was greater (27 g kg−1) in NT than in CT (24 g kg−1) when compared to non-degraded soil, where there was no difference in total organic C content after 8 years of different tillage treatment (Fabrizzi et al. 2003). The effect of reduced tillage on soil C restoration relates to improved soil aggregation (Paustian et al. 1997b) and decreased soil respiration (Buyanovsky et al. 1987) that leads to the buildup of C in soil. Halvorson et al. (2002) reported an inverse relationship between tillage intensity and soil C sequestration and reported an increase in soil C sequestration potential as the tillage intensity decreased (NT > MT > CT). Six et al. (2002) reported that in tropical and temperate soils, an increase in C levels was ~325 ± 113 kg C ha−1 year−1 under NT compared to CT. Tillage induced CO2 emission and a sharp increase in CO2 emission with a maximum value of 6.24 g CO2 m−2 h−1 under long-term (15 years) CT plots (Lopez-Garrido et al. 2009). The losses of C through CO2 emission were higher (801 and 905 g C m−2 year−1 for short (3 years) and long term (15 years), respectively in CT treatment compared to 764 and 718 g C m−2 year−1 for RT) and NT treatments practiced on long term (15 years), respectively (Lopez-Garrido et al. 2009). On the contrary, however, Minoshima et al. (2007) reported that despite low assimilation of newly added crop residue C in NT soil, a similar amount of CO2 was emitted from CT and NT, probably due to the high activity of microbes in the rhizosphere of the residue in NT soil.

Soil disturbance during tillage greatly influences soil C dynamics owing to accelerated erosion destructing soil aggregates and catalyzed microbial decomposition of soil organic matter (Singh and Benbi 2018b). The adoption of reduced tillage practices reduces C losses by offsetting CO2 emission and checking soil losses. In low-fertility tropical soils, NT is considered efficient soil management practice that improves the physical and chemical properties of soils (Lal et al. 1997). Gama-Rodrigues et al. (2010) reported that the extent of soil C sequestration depends upon the physical protection of soil organic C, as C occlusion in soil aggregates is the major mechanism for C protection in soils. About 40% higher soil aggregate stability has been reported under the NT management system compared to the CT management system (Jung et al. 2008). Patra et al. (2010) compared the traditional plow tractor-mounted cultivator, and power tillers for puddling the rice field in IGPs of West Bengal (India) to investigate the effect on C buildup in soil and reported that light soil puddling using traditional plow exhibited the highest buildup of soil organic C and microbial biomass. Dong et al. (2008) reported that after 5 years of moldboard plowing (MBP) and rotary tillage (RT) of soil, there was higher annual CO2 efflux from the soil because of less immobilization of soil organic C by microorganisms under long-term intensive tillage when compared to NT soils.

3.2 Zero Tillage Wheat

The number of sustainability issues pertaining to conventional rice–wheat cropping system reported in the region (Bhatt et al. 2019), namely, reduced yields and poor soil health (Bhandari et al. 2002), depleting ground water tables (Hira et al. 2004), and polluting air (Bijay-Singh et al. 2008). For irrigation purposes, mostly underground water is pumped up by submersible motors, which produce GHGs through hydrolysis of the applied N-fertilizers (Humphreys et al. 2010). For the harvesting of the field crops, especially rice and wheat, combines preferred in the region which left 0.3–0.6 m high anchored straw and lose straw in windrows. The management of crop residues especially rice is difficult due to its higher silica contents; hence, farmers generally used to burn it openly for timely sowing of the next upland wheat crop. Extensive tillage operations are required for straw management, coupled with the need to allow time for the straw to decompose sufficiently to avoid N immobilization (Gajri et al. 2002). Incorporation of the rice straw often delays wheat sowing beyond the optimum date (before 15th November) for maximum yield beyond which the wheat yields start decreasing. The farmers, therefore, opt for burning rice residues that result in air pollution and loss of organic C and nutrients, namely, ~35 kg N, ~21 kg K, and ~ 3 kg ha−1 each of P and S (Yadvinder-Singh et al. 2008). Residue burning exerts harmful effects on soil health due to the degradation of soil physical and biological properties (Yadvinder-Singh et al. 2005). The burning of rice residues is a major source of air pollution in the region, in the form of GHGs which led to global warming (Gupta et al. 2004). Zero tillage is the best option to date for the timely sowing of the wheat crop while ensuring successful and ecofriendly management of rice straw and saving presowing irrigation (Sidhu et al. 2007, 2008). Direct drilling of wheat seeds into the soil is considered a viable option to sow wheat seeds into the soil. Happy seeder—a modified zero tillage machine capability of seeding wheat seed in standing stubble—has been the most promising technology for eco-friendly rice residue management. The presence of the loose rice straw acts as mulch that further helps to regulate the soil temperature, reduces vapor pressure gradient and upflow of the vapor, reduces wind speed and its vapor lifting capacity, and finally, the soil evaporation that further encourages higher partitioning of the share of evaporation to transpiration (Balwinder-Singh et al. 2011; Balwinder-Singh et al. 2014). Reduced tillage benefits on land productivity (Paccard et al. 2015), water productivity (Guan et al. 2015), C intake in soil (Zhangliu et al. 2015), and finally on farmer’s livelihoods (Tripathi et al. 2013) are well recognized. The fuel-related CE emissions were significantly lower in the HS method by 35.9–94.1 kg CO2e ha−1 (25.5–47.3%) than the moldboard tillage, rotavator tillage, zero tillage (in residue removed fields), and the conventional tillage followed by residue burning (Singh et al. 2020a).

3.3 Cropping Systems and C Sequestration

Some interventions such as increasing cropping intensity than the fallow period (Hurisso et al. 2013; Lefèvre et al. 2014; Gan et al. 2012), including perennial forages, such as alfalfa (Medicago sativa L.) (Sainju and Lenssen 2011), planting high root biomass-to-aboveground biomass ratio plants (Negash and Kanninen 2015), and optimum and judicious fertilizer management (Zentner et al. 2011), helps in reducing C emissions in the atmosphere and thereby reduces the C footprints. For the optimization of C sequestration efficiency, cropping system (Wilson and Kaisi 2008; Singh and Benbi 2020b), intercropping (Makumba et al. 2007), cover cropping (Wang et al. 2010b), and ratoon cropping play a leading role in soil C sequestration (Wang et al. 2010a). In brown Chernozem soils of Saskatchewan, Canada, Campbell et al. (1995) have reported that during 12 years of continuous wheat (Triticum aestivum) cultivation, the soil has gained ~2.0 t ha−1 more C in 0–15 cm soil layer than in fallow–wheat cropping sequence, with most of the increase occurring during first 5 years of cropping. In dry land soils of North Dakota, Halvorson et al. (2002) reported that continuous use (12 years) of wheat–fallow system, even NT, results in loss of SOC, as fallow period represents the time of high microbial activity and decomposition of SOM with no input of crop residue. Kroodsma and Field (2006) reported that C sequestration was lowest in non-rice annual cropland that sequestered 9.0 g C m−2 year−1 of soil C and highest on land that switched from annual crops to vineyards sequestered 68 g C m−2 year−1 and land switched from annual crops to orchards sequestered 85 g C m−2 year−1 in comparison to rice field that sequestered 55 g C m−2 year−1 and referred this low C sequestration to the result of burning of rice residue after harvesting. Wang et al. (2010b) conducted a phytotron study to compare biomass accumulation and C sequestration by growing cover crops and evaluated that among winter cover crops, the highest and lowest amount of C assimilation occurred by bell bean (Vicia faba L.) 597 and 149 g m−2 by white clover (Trifolium repens), respectively, in fine sandy soils of United States. However, among the summer crops, sunhemp (Crotalaria juncea L.) accumulated the largest quantity of C (481 g m−2) while that by castorbean (Ricinus communis) was 102 g m−2 (Wang et al. 2010b). While studying the long-term effect (10 years) of intercropping, Makumba et al. (2007) reported C sequestration of 0.8 to 4.8 Mg C ha−1 in gliricidia–maize system when compared to 0.4–1.0 Mg C ha−1 in sole maize system. A net decrease in soil C (6.0–7.0 Mg C ha−1) in the upper 20 cm soil layer over initial C content was observed in the sole maize system. A total of 123–149 Mg C ha−1 was sequestered up to a depth of 200 cm through root biomass and pruning application in the gliricidia–maize system (Makumba et al. 2007). Makumba et al. (2006) reported that 11 years of intensive pruning of gliricidia trees may add 4.0–5.0 Mg DM ha−1 soil. They reported that SOC content in the upper 20 cm soil layer after 11 years of gliricidia pruning application was 3.0 g kg−1 higher in the gliricidia–maize system than in the sole maize system. Russell et al. (2005) reported that cropping systems that contained alfalfa in a rotation (corn–oat–alfalfa) had significantly (p ≤ 0.05) higher SOC stock than systems without alfalfa (continuous corn and corn–soybean). Furthermore, the highest soil CO2 emission was recorded from continuous corn cropping system than corn–soybean cropping system (Wilson and Kaisi 2008). The introduction of perennial legumes in semiarid climatic conditions has been known to reduce energy requirements by adding significant amounts of N to the soil (Entz et al. 2002). In the dry subhumid environmental conditions, alfalfa hay crop cultivation has been reported to contribute 84–137 kg N ha−1 (Kelner et al. 1997). Attempts must be made to plant more trees or crops with a higher root to shoot ratio, as greater will be then sequestered C into deep soils which will not be allowed to escape back from the soil to the atmosphere (Negash and Kanninen 2015).

Cropping systems significantly impacts soil C sequestration (Singh and Benbi 2020a) and the net ecosystem C budget of different wheat-based cropping systems (Singh and Benbi 2020b). Rice–wheat system had ~23% and 45% higher net primary production (NPP) compared with maize–wheat and cotton–wheat cropping system, respectively. The NPP through the aboveground residue biomass yield comprised the largest proportion (~48–50%) of the total NPP in three cropping systems, the highest being for rice and the lowest for cotton-based ecosystem (Fig. 2). Similarly, the NPP through different components was significantly higher for rice–wheat, followed by maize–wheat and the lowest for cotton–wheat cropping system. The net ecosystem C budget (NECB) was significantly lower for cotton, followed by maize and the highest for rice ecosystem (Fig. 3). It was negative for rice (scenario 1; continuously flooded), maize, and cotton, but positive for wheat. It was 2856, 2895, and 1801 kg C ha−1, respectively, for wheat sown in rotation with rice, maize, and cotton. The NECB for a rice–wheat cropping system was 2427, 2448, and 2459 kg C ha−1, respectively, under scenario 1 (continuously flooded), scenario 2 (intermittently flooded with single aeration), and scenario 3 (intermittently flooded with multiple aerations). The comparison of cropping systems revealed a significantly higher NECB for rice–wheat, compared with maize–wheat and cotton–wheat cropping system. Sharma et al. (2020a) reported increased SOC concentration due to regular cultivation of rice–wheat cropping sequence and that might be due to addition of higher fractions plant roots per year, flooded conditions which restrict the oxidizing microorganisms to oxidize the SOC into CO2 and use of heavy chemical fertilizers.

Fig. 2
figure 2

Different components of net primary production (NPP) through different components in various wheat-based cropping system (Source: Singh and Benbi 2020b)

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Fig. 3
figure 3

Net ecosystem carbon budget (NECB) for different wheat-based cropping systems (Source Singh and Benbi 2020b)

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3.4 Nutrient Management and C Sequestration

Nutrient management plays a significant role in soil C sequestration due to its impact on above-and below-ground biomass C input and cycling in ecosystems (Benbi et al. 2016; Singh and Benbi 2018a, 2021) (Table 1). The application of fertilizer nutrients increases the plant biomass and the quantity of crop residue returned into the soil (Sharma et al. 2020a; Singh et al. 2021a). Six et al. (2004) reported that improved N management is of utmost importance to realize complete benefits from C sequestered in soils to ensure mitigation of GHGs. The application of fertilizer-N had little effect on soil C sequestration although crop residue production was increased with N fertilization in spring wheat–winter wheat–sunflower and spring wheat–fallow cropping systems (Halvorson et al. 2002). Sainju et al. (2008) reported increased C input in soil due to cropping and N fertilization as a result of increased biomass in cotton–cotton–corn and rye/cotton–rye/cotton–corn cropping sequences. Nitrogen application in continuous corn and corn–soybean cropping system has been reported to check CO2 emissions from the soil, and the effect was pronounced at higher N applied plots (Wilson and Kaisi 2008). The SOC in control (no-N) plots increased from 37.2 to 38.8 Mg ha−1 in plots receiving 270 kg N ha−1 (Wilson and Kaisi 2008). Halvorson and Reule (1999) reported that fertilizer-N application for long term under NT practiced in dryland annual cropping in Colorado results in C sequestration through enhanced C sequestration efficiency. Conjoint application of NPK + FYM significantly increased SOC stock from 6.33 to 7.33 Mg C ha−1 compared to NPK alone (Singh and Benbi 2020a). NPK alone also maintained SOC stocks of 6.16 t C ha−1 which was higher than the controlled plots. Furthermore, soil organic C stocks were reported to be significantly lower by 14–18% and 12–14% in surface and subsurface, respectively, in imbalanced plots, compared to balanced (NPK) application of fertilizer nutrients.

Table 1 Effect of long-term manuring on soil organic C sequestration at experimental locations in India (Source: Swarup 1998; Rasool et al. 2007; Brar et al. 2013; Singh and Benbi 2018a)
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The average rate of change in soil organic C sequestration varied between 15 and 117 kg C ha−1 year−1 during long-term (10–25 years) fertilizer application (Table 3). Farmyard manure application combined with balanced fertilizer application (NPK + FYM) resulted in an 8–80% increase in soil organic C concentration, compared to NPK alone. At the surface (0–15 cm) layer, NPK + FYM contained the significantly highest soil organic C concentration (7.7 g kg−1) followed by NPK + crop residue (CR) (7.5 g kg−1) and NPK + green manure (GM) (7.4 g kg−1). There was a significant reduction in soil organic C concentration with the sole application of inorganic fertilizers (NPK) compared to those in the mixed organic and inorganic treatments. The lowest SOC concentration (3.6 g kg−1) in 0–15 cm layer was observed in the treatment of continuous cropping of rice–wheat over 25 years without any amendments. Mean soil organic C concentration in the profile increased from 2.4 g kg−1 in control to 4.1 g kg−1 in NPK + FYM. All the treatments showed a higher accumulation of soil organic C in the surface layer. Significant variations in SOC content were also observed in the subsoil layers; mean soil organic C content decreased from 6.4 at surface 0–15 cm to 1.8 g kg−1 at 45–60 cm soil layer.

3.4.1 Fertilizer-N Management and C Sequestration

The C footprints are described as the quantity of GHGs expressed in terms of CO2e emissions released in the atmosphere by an individual, organization, process, product, or event from within a specified boundary (Pandey et al. 2010). Jiang et al. (2019) reported that C footprints were positively correlated with fertilizer-N application rates, suggesting that GHGs emissions were strongly dependent on the rates of fertilizer-N application in rice cultivation. The C footprints in rice cultivation increased as the fertilizer-N application rates increased. The C footprints from N75 to N375 were increased by 15.1%, 31.2%, 39.7%, 41.8%, and 56.3%, respectively, compared to the control. The methane (CH4) emissions from the rice fields were the largest contributor to total C footprints, which increased initially followed by a gradual decrease and increase with increasing fertilizer-N input rates. The ecosystem service values of C sequestration decreased from positive to negative with increasing N fertilizer rates, suggesting that rice soils were transformed from a net C sink (0–300 kg N ha−1) to a net C source (375 kg N ha−1). Zhang et al. (2017) reported that grain production has higher C footprints of 4052 kg CO2e ha−1 or 0.48 kg CO2e kg for maize, 5455 kg CO2e ha−1 or 0.75 kg CO2e kg−1 for wheat, and 11,881 kg CO2e ha−1 or 1.60 kg CO2e kg−1 for rice cultivation in China. Of the total CE emissions, fertilizer-N contributes 8–49%, straw burning 0–70%, energy consumption by agri-machinery 6–40%, energy consumption for irrigation 0–44%, and the CH4 emissions from rice soils ~15–73%. On the other hand, the major C input was the returning of crop straw contributing ~41–90%, fertilizer-N application ~10–59%, and no-till farming practices contributing 0–10%. The C footprints concept has several implications. Therefore, the recent research focusing on the inclusion of soil organic C changes in addition to C footprint assessments for highlighting influences of crop production and soil management practices on total ecosystems’ C budget (Pandey and Agrawal 2014; Singh and Benbi 2020a).

3.5 Agricultural Waste Management and C Sequestration

Agri-waste, namely, crop residue (CR), farm yard manure (FYM), poultry litter (PL), and green manures (GM) application such as surface mulch can play an important role in the maintenance of soil organic C levels and productivity through increasing recycling of mineral nutrients, increasing fertilizer use efficiency, and improving soil physical and chemical properties and decreasing soil erosion (Hargopal-Singh et al. 2013). Furthermore, the C sequestration potential of added crop residue varies largely according to the total C content of the residue and the rate of total C input in the soil system (Kaisi and Grote 2007). After 19 years of continuous rice–wheat cropping, a highly significant positive linear relationship (R2 = 0.980) between stable C and cumulative C input from added organic sources showed that soil still has the potential to sequester more C with increasing C input from added organics (Ghosh et al. 2010). Fortuna et al. (2003) reported that compost application consecutively for 6 years has resulted in a 30% increase in resistant C pool and 10% in slow pool of C. Wang et al. (2010b) reported that mean net C remained in the crop residue after 127 days of decomposition period were 187 g m−2 and 91 g m−2, respectively, which represents approximately 73% and 52% of total biomass C for winter- and summer-grown cover crops. Sainju et al. (2008) reported that the soil organic C in the upper 20 cm soil layer after 10 years was greater with PL than with NH4NO3 applied on an equivalent N basis, resulting in a C sequestration rate of 510 kg C ha−1 year−1 with PL as compared with −120 to +147 kg C ha−1 year−1 with NH4NO3. An increase in soil organic C due to PL application compared with inorganic N fertilization in NT and CT system suggests the supplementation of 1.7 t C ha−1 year−1 from PL that was applied to supply 100 kg N ha−1 year−1 (Sainju et al. 2008). Averaged across tillage and cropping system, PL sequestered C at an estimated rate of 461 kg C ha−1 year−1 when compared to 141 kg C ha−1 year−1 (Sainju et al. 2008). The conjoint application of inorganic and organic fertilizers in NPK + CR (Rice straw) and NPK + GM(Sesbania sesban)-treated plots to rice–wheat cropping system practiced consecutively for 19 years in IGPs of West Bengal (India) has resulted in a significant increase in labile C fraction by 28% and 25%, respectively, over control (no-NPK/organics) (Ghosh et al. 2010). The highest value of labile C fraction in NPK + CR dressed plots has been ascribed to the effect of higher polysaccharide (cellulose and hemicellulose) content of crop residue that leads to higher production of labile C fractions compared to GM (Ghosh et al. 2010). NPK use for 45 years has resulted in ~3% increase in SOC content compared to ~115% increase in soil organic C in soils receiving NPK conjointly with FYM with an improvement in SOC from 4.95 to 7.30 t C ha−1 after 18 years that showed a C sequestration rate of 13 g C m−2 year−1 (Raji and Ogunwole 2006). The application of fertilizers and/or FYM increased the mean weight diameter of soil aggregates and thereby providing physical protection to soil organic C from decomposition (Banger et al. 2010). After 16 years of NPK application, there was a significant increase (~19.4%) in soil organic C under NPK-applied plots (0.430%) compared to control (0.360%). The integrated use of inorganic and organic fertilizers (NPK + FYM) and purely organic fertilizer application (FYM alone) has enhanced soil organic C by 33.4% and 36.3% over control (no-NPK/FYM). The concentration of water-soluble C (WSC), microbial biomass C (MBC), particulate organic matter (POM), and light fractions of C (LFC) were higher in organics that followed integrated system when compared to chemical (NPK) fertilizer dressed plots (Banger et al. 2010). A negative soil C sequestration range (−410 to −193 g C m−2) was observed in different crops including grass, cereals, and pulses, and however, recapitulates that C loss from soils could not be compensated through C inputs through plant photosynthates (Mu et al. 2006).

4 Land-Use Management and Soil C Sequestration

Soil organic carbon is influenced by the different soil and land management systems (Collins et al. 2000). Approximately ~10–30% (~7.0 Pg C year−1) of total global CO2 emission results from land-use change that is associated with deforestation, crop biomass burning, and conversion from natural to agricultural ecosystem (Prentice et al. 2001). Dowuona and Adjetey (2010) compared C stored by a Ferric Acrisol in the savanna zone of Ghana under different land-use systems and fertilized plot fallow and Leucaena woodlot. They reported that soils under the Leucaena woodlot stored the largest amount of C. An increase of ~200% in MBC has been reported under the switchgrass (Panicum virgatum L.) cropping system than in the corn–soybean cropping system (Kaisi and Grote 2007). The studies of Wang et al. (2009) revealed decreased soil organic C stocks by ~9.83 Mg C ha−1 in the upper 30-cm soil layer 28 years after shifting from grassland (meadow steppe) and by ~21.9 Mg C ha−1 42 years after shifting from grassland, which represents approximately ~10% and ~ 25% reductions, respectively.

Koul and Panwar (2008) found that in Tarai region of West Bengal (India), fallow land and agricultural fields sequester 5.86% and 4.73% C, respectively, compared to the natural forest having Shorea robusta canopy. In contrast, agroforestry, namely, tea garden and agrihorticulture contributed 24.2% and 9.1% C, respectively, compared to natural forests having Shorea robusta canopy (Koul and Panwar 2008). The rate of C sequestration in the fallow period was ~400% higher than the rate under continuous cropping (Raji and Ogunwole 2006). According to Lal (1999) of the 136 Pg C emitted due to land-use change, ~57.4% (~78 Pg C) was estimated to be the contribution of soil organic C pool. In a 45-year-old Gmelina forest, the soil C stock was 8987 g C m−2 compared to parts of the forest that were cleared and continuously cropped using conservation tillage practices for 15 years and had 75% lower C stock (1978 g C m−2) (Anikwe 2010). Gerzabek et al. (2006) reported that soil organic C of grassland soils was 1.8 times greater than that of cropland plots in Eutric Cambisols of Sweden. Singh and Benbi (2018a) reported that the C preservation capacity of water-stable aggregates was significantly higher in soils under grasslands in contrast to eroded slopes, which had the lowest C preservation capacity.

The hilltop and cropland soils, however, did not differ significantly with regard to C preservation capacity of water-stable aggregates. The formation of water-stable aggregates has been related to soil organic C concentration (Benbi et al. 2016). Benbi et al. (2012) reported that the soils under rice–wheat system had significantly lower soil organic C concentrations compared to those under maize–wheat and agri-forestry land-use systems. As compared with the rice–wheat cropping system, the soils under agro-forestry and maize–wheat land-use systems had ~88% and 65% higher in soil organic C concentration, respectively. In another study, Benbi et al. (2015) reported that the soils under different land-use systems did not differ in C:N ratios except that under agro-forestry compared to maize–wheat and the rice–wheat cropping systems. The total organic C pool was higher (p < 0.05) in the uncultivated soils than the cultivated soils, but differences among cropping systems were nonsignificant. For restoring the degraded and waste lands, different improved practices, namely, zero tillage, legume intercropping, retaining crop residues on the soil surface, cover crops, integrated nutrient management, and agro-forestry, must be adopted (FAO 2007). Human activities accelerate the pace of different physicochemical reactions in the soil (Scharlemann et al. 2014; Smith et al. 2008). West and Marland (2003) estimated the net C flux for the United States with a change in the tillage intensity (Table 2).

Table 2 Average net carbon flux for the United States with change in tillage from conventional tillage (CT) to zero tillage (ZT) (Source: West and Marland 2003)
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Globally, net emissions of 1.1 ± 0.7 Pg C year−1 were recorded from 2000 to 2010 which were mainly due to extensive forest tree cuttings for agricultural production (Don et al. 2011; Houghton 2003). The Indian tropical conditions are responsible for the higher C turnover and sequestration (Malhi et al. 2004). The warmer climatic conditions are considered responsible for the higher C emissions than the colder regions (Zech et al. 1997). Furthermore, C stocks decreased to ~25–30% on shifting from the forest to the cultivation (Don et al. 2011); therefore, land use must be sustainable if soil C stocks are to be maintained (NETL 2010). A shift to agricultural land use from the forest lands in year zero resulted in higher soil organic C stocks with improved management practices of reduced tillage, mulching, and so on (Sanderman and Baldock 2010) (Fig. 4). Instead, its management of the mined lands, forest lands, rangeland, grassland, and agricultural lands is also very important for sequestering the C in the terrestrial ecosystems.

Fig. 4
figure 4

Relationship between SOC stocks and aging by hypothetical field trial (Source: Sanderman and Baldock 2010)

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5 Legumes and C Sequestration

Growing of the leguminous crops, namely, lentil, guar, moong in between the conventional rice-based cropping sequences, is considered as one of the most important interventions for improved C sequestration and reduced C footprints of the system as a whole including the intervening periods (Poeplau and Don 2015). Legumes are a better fit for the diversification option due to their shorter stay in the field, ability to tolerate different stresses, and finally ability to sequester C (Ghosh et al. 2020). Poeplau and Don (2015) delineated an annual organic C sequestration of 0.32 t ha−1 with the inclusion of leguminous crops. Lal (2010) reported enrichment of soil organic C under proper crop rotation with legumes due to higher exchange efficiency of residue-derived C to soil C pool. Legumes on the long run assured N availability which produces higher biomass C. These crops promote C impounding potential of succeeding crop gown in the rotation, improving the microbial functions, and biomass fabrication by successive crop and finally improving soil quality (Yadav et al. 2017). The inclusion of leguminous crops in cropping systems leads to increased nutrient use efficiencies and enhanced root biomass which eventually enhances C inputs and labile C pools in the soil (Lal 2010).

Legume crops such as green manure, cover crops, and forage promote C and N in the soil system, thereby improving soil physical, chemical, and biological properties that enhance the crop grain yields (Bedoussac et al. 2015) while reducing the C footprints. The increased mechanical operations and C footprints due to the inclusion of cover crops (Saini and Bhatt 2020) are offset by the positive prevalence of cover crops on the mitigation of GHGs with increased C sequestration. Once C is lost into the atmosphere as GHG, it contributes toward GWP (Singh and Benbi 2020b). Crop diversifications with legumes not only reduce the C footprints but also restore soil organic C stocks due to increased photosynthetic activities throughout the year (Dhakal et al. 2015). Nonetheless, the C:N ratio and concentration of nutrients in crop residues of the legumes are relatively higher than in other cereals crops (Srinivasarao et al. 2011).

6 Crop Cultivars and Soil C Sequestration

Carbon input into the soil depends inter alia on crop cultivars and resultant biomass. The crop cultivars with deep roots and large leaf foliage had higher C sequestration and low C footprints. The terrestrial and atmospheric C pools strongly interact with one another. The development of new plant cultivars using biotechnological interventions with similar yield potential and lesser stay in the field lowers fertilizer-N requirements and leads to lesser emission of CO2 and ammonia (NH4) gas which finally reduces both C footprints (Lal et al. 1998). The selection of crop cultivars had a significant effect on soil C status, water, and energy footprints. The crop cultivars that had a short duration in the field had low irrigation water requirements and high-water productivity (Singh et al. 2020c). The short- and medium-duration crop cultivars had higher water productivity due to reduced soil water evaporation (Singh and Saini 2011). In northwestern India, a long duration rice variety (Pusa-44) that takes 160 days to mature consumes a significantly higher amount of irrigation water than the short duration varieties, namely, PR-126 and PR-127 (PAU 2020) which take only around 123 and 137 days and thus have potential to save water by 15–20% (Balwinder-Singh et al. 2015; PAU 2020). The results of 550 farmer’s field demonstrations conducted in southwestern Punjab (India) revealed that grain yield of rice variety PR-122 was significantly higher by ~11.1% and 14.5%, compared to PR-126 and PR-124, respectively (Singh et al. 2020c). They have reported that the production efficiency of 54.5 kg ha−1 day−1 was higher for PR-126, compared to PR-124 (50.0 kg ha−1 day−1) and PR-122 (50.6 kg ha−1 day−1). The economic efficiency of PR-124 was lower by ~Rs. 111.9 ha−1 day−1 and Rs. 43.6 ha−1 day−1 than the PR-126 and PR-122, respectively. The water use efficiency was higher for PR-126, compared with the other two genotypes. Therefore, the adoption of short-duration rice cultivars, demanding lower volumes of irrigation water when compared to the longer duration one (Jalota and Arora 2002; Arora et al. 2008; Jalota et al. 2009) had lower C footprints (Singh and Benbi 2020b). The comparison of three different irrigation management regimes, namely, Scenario 1 (continuously flooded), Scenario 2 (intermittently flooded with single aeration), and Scenario 3 (intermittently flooded with multiple aerations) revealed that the global warming potential (GWP) for rice cultivation in northwestern India was 2.94, 2.41, and 2.13 Mg CO2e ha−1 year−1, respectively (Singh and Benbi 2020b). Nonetheless, the inclusion of suitable legumes or perennial forages such as alfalfa (Medicago sativa L.) reduces the C footprints in comparison to the annual sequences due to higher belowground C input (Sainju and Lenssen 2011). C sequestration in soils had a key role in reducing the C footprint of crop cultivation and in improving soil health (Benbi et al. 2016; Singh and Benbi 2018a). Attempts must be made to sequester a greater fraction of the atmospheric C back in plant biomass for a longer period of time for better C stabilization; otherwise, the sequestered C will be released back into soil within a shorter period and responsible for causing different adverse effects, namely, global warming and so on.

7 Crop Diversification and C Sequestration

Crop residues in terms of both quantity and quality affect the soil organic matter (Srinivasarao et al. 2013). Among different options purposed for improving the sustainability cropping systems, crop diversification seems to be quite effective in decreasing the C footprints and enhanced C sequestration. For example, if in a rice-based cropping system, rice is being replaced with maize or other oilseed or pulse crops; then, energy footprints (as no intensive tillage and fertilization) (Singh et al. 2019a, b), water footprints (as no puddling and reduced conditions), and ultimately the C footprints could be sustainably reduced (Singh et al. 2020a; Singh and Benbi 2020b). Therefore, for reduced C emissions and C footprints, rice crops must be diversified with the vegetables, pulses, maize, and oilseed crops. The inclusion of legumes or pulse crops in cereal-based cropping systems enriches the soil with different nutrient and root exudates that promoted the soil structure and aggregation. Therefore, any crop diversification option which adds a good quantity of crop residues in the soil back will certainly improve the SOC stocks within different soil (Singh et al. 2018b; Singh and Singh 2017; Dhillon et al. 2020), which is important for the good soil health and land productivity (Majumder et al. 2008). Green manuring, keeping less fallowing and winter cover, and adding legumes that fix atmospheric N are required for reducing the C footprints (Flynn et al. 2009). The buildup of SOC concentration with crop diversification must concentrate on increased crop biomass and organic matter humification. The atmospheric C is sequestered in the soil through the roots as organic acid, phenolic acid, and amino acid. According to Mandal et al. (2007), up to ~82% of the applied or added C is lost to the atmosphere, which needs to be cut down through different options including crop diversification as the highest C fixation reported in the rice–wheat–jute cropping system (535 kg ha−1year−1) followed by rice–mustard–sesame (414 kg ha−1year−1) than rice–fallow–rice (402 kg ha−1year−1) at CRRI, Cuttack. The addition of pulse crops in cereal-based cropping systems could serve the purpose and have a significant role in improving soil health (Porpavai et al. 2011) by fixing a higher proportion of atmospheric C back into the soil in different C pools of variable oxidizability (Table 3). The less labile C was the highest SOC fraction in soils under different cropping systems (Ghosh et al. 2012). They have reported that higher crop biomass maintained greater SOC under rice–wheat–mungbean and rice–wheat–rice–chickpea cropping systems in the IGPs. Under the crop diversification, the incorporated legumes fix biological N2 and produce root exudates besides leaf litter, and the deep root system helps in improving the C economy of soils when compared to conventional systems. The maize–wheat–mungbean and pigeonpea–wheat systems are reported to significantly increase the SOC concentration by ~11% and 10% and the MBC by ~10% and 15%, respectively, (Venkatesh et al. 2013). Therefore, crop diversification sustainable options with legumes will certainly serve the purpose to improve root and crop biomass additions in soils which further promoted higher C stocks and hence soil health with reduced C footprints in the soils. But, still, there is a need to give more attention to this option for all kinds of lands with divergent soil textural classes in different agroclimatic regions of the country. Identifying sustainable diversification systems for higher C sequestration and increased productivity will certainly help to mitigate the climate change effects on one side while improving the livelihoods on the other (Bhatt et al. 2021).

Table 3 Effect of inclusion of pulses in rice-based cropping systems on soil organic carbon fractions of different oxidizability in Inceptisols of Indo-Gangetic Plain (IGP) zone (Kanpur), India (Source: Ghosh et al. 2012)
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8 Soil Conservation Practices and C Sequestration

In the hilly tracts, the landscapes are generally prone to soil erosion by both wind and water (Arora et al. 2008; Singh and Benbi 2018b). These landscapes generally had coarse-textured soils low in organic matter and poor in fertility. The high-intensity rains on steeper slopes on soils with lesser amounts of organic matter results in the detaching of the soil particles from their parent material and transported with the water or wind to remote distances (Singh and Benbi 2018b). The ecosystems require an urgent need to control soil erosion to improve C sequestration, soil health, and soil productivity. In northwestern India, accelerated erosion has been taking place during the last 50 years, and these landscape positions have been losing 0.12 Mg C ha−1 year−1 through soil erosion (Singh and Benbi 2018b). In the light of scientific knowledge, the following indigenous techniques for efficient soil and water management have been suggested to improve land and water productivity (Bhatt and Kukal 2016). Soil organic C potential and C sequestration rates of degraded lands revealed the highest C sequestration potential (Table 4).

Table 4 Soil organic C sequestration potential and C sequestration rates through restoration of degraded soils (Source: Srinivasarao et al. 2013)
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9 Crop Residue Management and C Sequestration

In India, rice-based cropping systems are intensively cultivated on ~90% of the area in Indo-Gangetic Plains (IGPs) (Janaiah and Hossain 2003; Bhatt et al. 2021). The impact of residue removal on soil organic C concentration and stocks across different soils in the U.S. Corn Belt region has been shown in Table 5. In the intensive cultivation in these fertile plains, a large proportion of total crop residue generated (500–550 Mt. year−1) is burnt in situ in open fields (MOA 2012; Singh et al. 2020a). The open field burning of crop residue is adversely affecting the sustainability of rice–wheat system due to increased C footprints due to decreased C sustainability which has been a great challenge in front of agricultural scientists (Bisen and Rahangdale 2017). The data illustrate that cereal-based cropping systems had the largest (~58%) share toward total crop residue produced, of which ~25% is produced under the rice–wheat cropping sequences (Sarkar et al. 1999).

Table 5 Impacts of residue removal on soil organic C concentration and stocks across different soils in the U.S. Corn Belt region
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The rice straw burning contributes ~0.05% of the total GHGs emissions in India, which has been the major concern for human and environmental health (Gadde et al. 2009). Apart from the loss of C, up to 80% loss of N and S, 25% of P, and 21% of K occur during burning of crop residues (Ponnamperuma 1984; Yadvinder-Singh et al. 2005). It is estimated that one tone of rice straw contained 5–8 kg of N (Dobermann and Fairhurst 2002); therefore, an annual rice–wheat cropping system with an average production of 7 t ha−1 of rice +4 t ha−1 of wheat grains removed more than ~300 kg N, ~30 kg P and ~ 300 kg K ha−1 (Singh and Singh 2001). Therefore, burning the crop residues has not been a viable option and therefore requires immediate attention.

10 Biochar Application and C Sequestration

Biochar prepared through pyrolysis, gasification, and hydrothermal carbonization has ~70% of C, which might be emitted into the atmosphere. Biochar application in soils enhance the SOC and thereby favors the soil’s physicochemical and biological properties and soil health (Sohi et al. 2010; Day et al. 2005; Srinivasarao et al. 2013). The small-scale biochar production proves to be economical and sustainable (Pratt and Moran 2010). Being a fine-grained, soft, C-rich source with highly porous structure and high surface area, biochars are considered important regarding C sequestration and reducing C footprints in crop production (https://www.pau.edu/content/pf/pp_kharif.pdf). The biochars are also considered as efficient liming materials for the reclamation of acidic soils. The biochars had the potential to mitigate ~12–50% of anthropogenic C emissions depending upon the material used, pyrolysis conditions, and energetic performance of the biochar production system (Cayuela et al. 2010). Quite often, biochars prepared with thermal decomposition of crop or plant biomass waste in three ways, namely, pyrolysis, gasification, and hydrothermal carbonization, where the material is heated up in the absence of the O2 which produced volatile gas leaving behind C-rich biochar (Sohi et al. 2009) which on application helps in improving the water and nutrient holding capacity of soils.

Prali Char is prepared in a pyramid or dome type kiln made up of bricks and clay which is dome-shaped (height = 14 ft, diameter = 10 ft) and can accommodate 12 t of rice straw. The whole process of making prali char usually takes ~10–12 h. On average, prali char contains 30–36% C, 0.5–0.6% N, 0.16–0.22% P, and 1.6–2.2% K. Field application of this in rice and wheat at 5 t ha−1 saves 40 kg N ha−1 besides increasing crop productivity and improving soil health. It uses perlite as an insulator between the two fire brick walls to check the heat loss. The drums are filled with agricultural residues with the provision to escape syngas. Temperature is hiked to 300–400 °C for proper heating of residues. This method requires only ~2 hours for the preparation of good quality biochar.

11 Nitrogen Transformation Inhibitor and C Sequestration

The misuse or overuse of chemical fertilizers has been the major cause of soil, water, and air pollution (Fowler et al. 2013; Neubauer and Megonigal 2015; IPCC 2014). Nitrogen fertilizer is one of the main source of nitrous oxide (N2O) production in agricultural land (Bouwman et al. 2002) and is further affected by the form (Dobbie and Smith 2003), amount (Ma et al. 2010), and fertilization method (Lin et al. 2010; Liu et al. 2011). Globally, N use efficiency of cereals is ~33% on an average (Raun and Johnson 1999). The N recovery efficiency of fertilizers in lowland rice is reported to be ~40% (Fageria 2014; Fageria et al. 2007) which highlighted a significant loss to the biosphere through leaching, volatilization, and denitrification causing environmental pollution. Around 70% of all plant nutrients at a global level are received from fertilizers (Ayoub 1999; Khalil et al. 2011). Therefore, improving N use efficiency has significance in achieving sustainability which can be ensured following different management strategies. For example, the use of N transformation inhibitor and slow release fertilizers, e.g., neem-coated urea or polycoated urea (Shaviv and Mikkelsen 1993) has been advocated due to improved N use efficiency, land productivity (Shoji et al. 2001), mitigation of N2O emissions, and reduce the C footprints of the system (Jiang et al. 2010).

12 Agroforestry and C Sequestration

Agroforestry enhances C sequestration rates and thus the soil health (Benbi et al. 2012; Dhillon et al. 2020; Sharma et al. 2021a). Dhillon et al. (2020) reported that total organic C stocks in soils were related to the age of the agroforestry system. They have reported that total organic C was higher in soils under 20-year agroforestry compared to the soils under the relatively younger agroforestry system. The organic C stocks in surface soil under the 20-year agroforestry system were significantly higher, although TOC stocks in soils under 10 and 15 year of agroforestry did not differ significantly. In the subsurface soils, TOC stocks were significantly higher under agroforestry older than 10 years, while TOC stocks did not differ significantly under 10-, 15-, and 20-year agroforestry systems. The C storage capacity of different agroforestry models is detailed in Table 6.

Table 6 Carbon storage capacity of the soils under different agroforestry models
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13 Conclusions

The present review focused on effects of conventional land management practices, namely, intensive tillage, residue burning in open, puddling operations, use of higher N fertilizers, and so on on the soil C stocks and GHGs emissions in comparison to the recommended technologies. Carbon stocks are the core of the terrestrial ecosystem which must be enhanced by sequestering the higher fraction of C back in the soil for a longer period of time and by reducing GHGs emissions. C sequestration is enhanced by converting the degraded or waste lands under forest/agroforestry. In rice-based cropping sequences, anaerobic conditions resulted in the production of GHGs, which complicate the systems’ sustainability. Scientists across the regions suggested many technological interventions for enhancing C sequestration with reduced C footprints in the agricultural sector. Among others, conservation tillage, zero tillage in standing rice stubbles, N and agri-waste management, land use management, legume inclusion, crop cultivars, crop diversification, biochar application, and water and nutrient use efficiency within a cropping system are important. The government and private agencies and other farmer’s welfare organizations need to come forward for farmers’ welfare by providing subsidies on agri-machinery for in situ crop residue management to enhance C sustainability due to reduced C footprints.