Effect of ConservationTillage and Residue Management on Soil Organic Carbon Storage, Ecosystem Dynamics and Soil Microbial Biomass in Sub-tropical Agro-ecosystem: A Review

Investigating microbial metabolic characteristics and soil organic carbon (SOC) within aggregates and their relationships under conservation tillage may be useful in revealing the mechanism of SOC sequestration in conservation tillage systems. Crop residue retention has been considered a practicable strategy to improve soil organic carbon (SOC) but the effectiveness of residue retention might be different under varied tillage practices. The concentrations of SOC in the 0–10 cm layer were higher under no-tillage than under conventional tillage, no matter whether crop residues were retained or not. Residue retention increased SOC concentrations in the upper layers of soil to some degree for all tillage practices, as compared with residue removal, with the greatest increment of SOC concentration occurred in the 0–10 cm layer under rotary tillage, but in the 10–30 cm layer under conventional tillage. The stocks of SOC in the 0–50 cm depth increased from 49.89 Mg ha–1 with residue removal to 53.03 Mg ha–1 with residue retention. However, no-tillage did not increase SOC stock to a depth of 50 cm relative to conventional tillage, and increased only by 5.35% as compared with rotary tillage. Previous crop residue (S) treatments had higher SOC concentration of bulk soil (12.9%), >0.25 mm aggregate (11.3%), and <0.25 mm aggregate (14.1%) than residue removal (NS) treatments. Compared with conventional intensive tillage (CT) treatments, no tillage (NT) treatments increased MBC by 11.2%, 11.5%, and 20%, and dissolved organic carbon (DOC) concentration by 15.5%, 29.5%, and 14.1% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Compared with NS treatments, S treatments significantly increased MBC by 29.8%, 30.2%, and 24.1%, and DOC concentration by 23.2%, 25.0%, and 37.5% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Overall, straw return was an effective means to improve SOC accumulation, and soil quality. Straw return-induced improvement of soil nutrient availability may favor crop growth, which can in turn increase ecosystem C input. Tillage reduction and residue retention both increased the proportion of organic C and total N present in soil organic matter as microbial biomass. Microbial immobilization of available-N during the early phase of crops and its pulsed release later during the period of greater N demand of crops enhanced the degree of synchronization between crop demand and N supply. The maximum enhancement effects were recorded in the minimum tillage along with residue retained treatment. Furthermore, conservation tillage increased SOC in aggregates in the topsoil by improving microbial metabolic activities in the Sub-tropical Agro-ecosystem.