Effects of conservation agriculture on carbon mineralization: A global meta-analysis

Abstract

Soil carbon (C) sequestration, as an important means of mitigating climate change, is influenced by C mineralization. No-till (NT) and residue retention (RR) developed rapidly due to their soil C sequestration function. However, their effects on soil organic carbon (SOC) mineralization are still controversial, with positive and negative effects under NT and unclear effects on mineralization ratios under RR reported, which hinders the ability to predict SOC sequestration efficiency, SOC stabilization and CO2 emissions. Therefore, a global meta-analysis based on 132 peer-reviewed papers was used to investigate the effects of NT and RR on absolute mineralizable carbon (AMC) and specific mineralizable carbon (AMC per unit SOC, SMC) in laboratory incubation studies. The results showed that NT significantly increased AMC in surface (0–5 cm) and subsoil (> 20 cm) where it had been practiced over the long-term (>15 years), without crop rotation, and in alkaline soils (pH >7.8) compared to conventional tillage. RR generally increased AMC, and its negative effect on SMC was significant in soils with a high input of N fertilizer (> 300 kg N/ha) and sandy soils compared to residue removal. NT significantly reduced SMC in neutral and acidic soils (pH < 7.8), or compared to chisel plow or rotary tillage. Furthermore, RR and NT generally improved soil indicators except ammonium nitrogen and bulk density, and RR improved most of them significantly. The correlation analysis revealed that the change in AMC was significantly positively correlated with the indicators related to C/N, while SMC was significantly negatively correlated with SOC concentration. In general, both NT and RR significantly increased AMC, while SMC increased significantly with RR only, and NT+RR significantly decreased SMC. When combined with other measures, e.g. N application with RR, and applied in combination, NT and RR can increase SOC while decreasing its mineralization, thus improving the sequestration of C.