Effects of tillage and residue management on soil aggregates and associated carbon storage in a double paddy cropping system

Abstract

Soil structure stability and carbon (C) storage play an important role in farmland soil conservation, nutrient supply potential, and climate change mitigation. Different tillage systems can affect the soil structural stability and C storage, thus affecting the ecological security of farmlands. We evaluated the long-term effects of tillage systems on soil water-stable aggregates, aggregate-associated C, and C storage in a double rice (Oryza sativa L.) production system in southern China. Four tillage treatments were investigated, including no-till with residues retained on the soil surface (NT), rotary tillage with residue retention (RT), plow tillage with residue retention (PT), and plow tillage with residue removed (PT0). The long-term application of straw returning can significantly increase the stable macro-aggregates, macro-aggregate-associated C, and SOC. There were significant differences in C storage between macro-aggregates and micro-aggregates. With the increase in SOC, more C was fixed in the macro-aggregates (especially WSA>2mm) rather than the micro-aggregates, and aggregate-associated C (WSA<0.053mm) was a stable C pool in all soil depths under tillage systems. The adoption of NT enriched surface SOC with more macro-aggregates, especially at the 0–5 cm, but the gap between NT and other tillage in macro-aggregates fractions and aggregate stability has been shrinking caused by C enrichment. The treatment NT can increase surface C storage (0–5 cm), but the highest C accumulation was observed at RT in the 0–30 cm soil layer. Based on our results, strategic tillage (a combination of no-till and tillage) may be an effective approach to increase C storage in double rice system.