Since SOC is essential for soil fertility and climate change mitigation, alternative production practices have been adopted globally to increase soil C storage (Lal, 2004b; Sauvadet et al., 2018). A comprehensive analysis in China reported that NT led to SOC depletion in the 30–40 cm of soil compared to CT (Du et al., 2017). However, using a set of crop models (APSIM-NWheat, DSSAT, EPIC, SALUS) calibrated and validated with datasets from long-term experiment data, Iocola et al. 2017) illustrated that tillage practices can be an effective option to increase SOC in the 0-40 cm of soil.
Similarly, a study in China, using 95 paired comparisons, reported that NT significantly improved SOC stock in the 0–20 cm of the ground on average over CT (Du et al., 2017). In addition, residue retention can directly increase soil C input, improve soil structure and nutrient availability, and increase soil microbial populations (Johnson and Hoyt, 1999; Li et al., 2018). The increased cultivation intensity can increase the production of both above and below ground biomass, which can later be included in the total SOC pool (Luo et al., 2010).
Other factors, such as study duration (Mondal et al., 2020), climatic conditions (Sun et al., 2020) and soil texture (Wan et al., 2018), have also been shown to be crucial in influencing the direction and magnitude of changes in SOC storage in response to conservation tillage practices (González-Sánchez et al., 2012; The natural logarithm of the response ratio (lnRR) of soil C (Mg ha−1) between means (𝑋̅𝑡 −NT, RT , NTR or RTR) over the control agents (𝑋̅𝑐−CT) was calculated according to Osenberg et al. To derive the overall response effect of the treatment group versus the control group, the weighted response rate (RR++) between treatment and control groups was calculated according to Hedges et al.
Correlations between independent variables, environmental and management factors, and the response ratio of SOC stock, with or without residue retention, were detected using Pearson correlation analyzes by the "correlation" package (Lüdecke et al., 2019) in R (version 3.4) .2).
Results
When the study duration was <6 years, NT, but not RT, increased SOC stock relative to CT (Fig. 4a, p < 0.001), and NT significantly increased SOC stock compared to RT. For RTR, all conservation tillage practices significantly increased SOC stock compared to CT when the study duration is between 6 and 12 years (Fig. 4b). Changes in SOC stock were significant for all comparisons in the topsoil except for NTR vs.
Only RT, NT and RTR had significant effects on increasing SOC stock compared to CT in clay soils (Fig. 6a). For silt soils, except for RTR, all treatments significantly increased SOC stock relative to CT (Fig. 6b). For sandy soils, NT, but not RT, significantly increased SOC stock compared to CT (Fig. 6d), and CTR, RTR, and NTR also significantly increased SOC stock compared to CT.
In humid areas, treatments increased SOC stock (Fig. 7b, p < 0.01), with the exceptions of NT and RT compared to CT. For the perhumid areas, NTR significantly reduced SOC stock compared to RTR (Fig. 7c), while the rest of the conservation tillage practices increased SOC stock (p < 0.01).
Discussion
Altogether, the subsoil has less opportunity to acquire SOC stocks in cultivated areas using conservation tillage practices (Mondal et al., 2020). This finding is in agreement with a synthesis study in Spain, which showed that C storage under NT was five times higher than under RT (González-Sánchez et al., 2012). Furthermore, a long-term conservation tillage field study reported that C loss rates were lower under NT than RT in Kansas, USA (Fabrizzi et al., 2007), resulting in greater SOC stock under NT than RT.
Other case studies have also reported that the change in C stock is related to soil storage capacity, which is related to the duration of minimum tillage practices (Lu et al., 2009; Luo et al., 2010). Our results are in agreement with a previous meta-analysis based on data from China, which reported that NT plus residue retention effectively increased SOC sequestration (Du et al., 2017). Compared to minimum tillage practices alone, residue retention was more promising in increasing SOC stock (Han et al., 2018; Lu et al., 2009).
Therefore, more organic C input and less frequent soil disturbance may lead to greater SOC accumulation (Hubbard et al., 2013; Liu et al., 2014). A significant priming effect was observed in the topsoil (Salome et al., 2010), which indicated that C availability was the most important limiting factor in C dynamics in the topsoil (Fig. S3). Residue retention facilitates C limitation (Liu et al., 2014), and thus increases the size of the soil microbial population (Li et al., 2018), which can improve aggregate.
As expected (Fig. S4), SOC accumulated faster in the wetter regions than in the drier regions (Zhang et al., 2015), and MAT has strong positive correlations with MAP (Fig. S2). For example, an increase in SOC stocks in southern Africa with conservation tillage practices was lower than expected due to limited biomass production (Cheesman et al., 2016). Ecosystem responses to the combination of temperature and altered precipitation tended to be smaller than expected from the single factor responses (Wu et al., 2011).
Adding organic acids to soil using an artificial root system, Keiluweit et al. 2015) observed that oxalate increased SOM decomposition while decreasing soil pH. Clay content is considered a critical property of soils that affects their C storage capacity (Novelli et al., 2017; Wan et al., 2018) and soils. However, residue retention contributes more to increasing SOC stock in coarse-textured soils than in fine-textured soils (Wan et al., 2018), which was supported by our findings (Figure 6).
Conclusions
One limitation of the current study is the lack of available research data from Africa and South America, where conservation tillage practices have been widely adopted (Cheesman et al., 2016; Swanepoel et al., 2018). This stifles our synthesis in improving our understanding of the response of SOC stocks to cropland management such as minimum tillage and residue retention. No-tillage reduces CO2 emissions the most in arid and sandy soils: results of a meta-analysis.
Long-Term Effects of Contrasting Tillage on Soil Organic Carbon, Nitrous Oxide and Ammonia Emissions in a Mediterranean Vertisol Under Different Crop Sequences. Soil Carbon Sequestration in Kansas: Long-Term Effect of Tillage, N Fertilization, and Crop Rotation, The Fourth USDA Greenhouse Gas Conference, Marriott Hotel, Stadium Ballroom, Second Floor. Straw incorporation increases crop yield and soil organic carbon sequestration, but varies under different natural conditions and agricultural practices in China: a systems analysis.
Conservation agriculture practices increase soil microbial biomass carbon and nitrogen in agricultural soils: a global meta-analysis. Liming effects on soil pH and crop yield depend on liming material type, application method and amount, and crop species: a global meta-analysis. Residue retention and minimum tillage improve the physical environment of soil in croplands: A global meta-analysis.
Organic amendments increase crop yields by enhancing microbe-mediated soil action of agroecosystems: a meta-analysis. Soil organic carbon dynamics collectively controlled by climate, carbon input, soil properties and soil carbon fractions. A global analysis of the impact of zero tillage on soil physical condition, organic carbon content and plant root response.
Increased cultivation intensity improves the supply of crop residues to the soil and aggregate-associated soil organic carbon stocks. Soil quality under on-farm conservation practices in Argentina's southern semi-arid pampa region. The benefits of conservation agriculture on soil organic carbon and yield in southern Africa are site specific.
Response of mineral soil carbon storage to crop residue retention depends on soil texture: A meta-analysis. Soil carbon dynamics following land-use change varied with temperature and precipitation gradients: evidence from stable isotopes.
