Abstract:
As an important element of anthropogenic soil management practices, tillage typically influences soil organic carbon (SOC) turnover by altering soil physical and chemical properties or directly manipulating the distribution of crop residues within soil. With a specific focus on the dryland wheat fields on the Loess Plateau, in this study, we conducted a field experiment from 2018 to 2020, in which we adopted a single-factor completely randomized block design, and established the following three tillage patterns during the summer fallow period: no tillage (FNT), deep plowing (FPT) and subsoiling (FST). Soil samples were collected from the 0−50 cm soil layers following the dryland wheat harvest in June 2020, and we analyzed the accumulation and mineralization of SOC and the relationships with physicochemical properties under different summer fallow tillage patterns. The results revealed that at soil depths of 0−10 cm, there were significantly higher SOC stock (SOC
stock), SOC sequestration (ΔSOC
stock), SOC sequestration rate (SOC
stock-rate) and SOC sequestration efficiency (SOC
stock-efficiency) in soils under the FNT treatment, which would be advantageous with respect to SOC sequestration within the surface soil. Within the 0−50 cm soil profile, compared with the FNT treatment, the FPT and FST treatments contributed to significant increases of 9.90%−10.40% in SOC
stock, as well as ΔSOC
stockand SOC
stock-rate, although there were no significant differences detected between the FPT and FST treatments. Moreover, the linear fitting results revealed that SOC
stock-rate initially increased and subsequently declined in response to an increase in carbon input from exogenous residues. Following 40 days of laboratory incubation, the significantly highest cumulative mineralization of SOC was observed within the 0−30 cm soil layer under FPT treatment and within the 30−50 cm soil layer under FST treatment, and we found that the potentially mineralizable carbon was essentially consistent with the cumulative mineralization of SOC. With respect to SOC mineralization rate, we observed the trend of FPT > FNT > FST within the 0−30 cm soil layer, and compared with the FST and FNT treatments, levels of mineralization rate were found to be significantly lower in the 30−50 cm soil layer under FPT treatment. Furthermore, on the basis of redundancy analysis, we identified the soil available nitrogen (AN) content, pH, and soil available phosphorus (AP) content as key factors contributing to differences in the accumulation and mineralization of SOC in soil subjected to different tillage treatments, notably the significant relationships between AN content and each of these tillage practices. Overall, under the assessed experimental conditions, the FNT tillage pattern was established to have significant short-term advantages with respect to carbon sequestration in the surface soil. On the basis of the observed effects on SOC sequestration and mineralization, an FST tillage pattern is recommended as a measure for promoting carbon sequestration within the 0−50 cm soil layer of dryland wheat fields on the Loess Plateau, China.