Straw return increases crop production by improving soil organic carbon sequestration and soil aggregation in a long-term wheat- cotton cropping system

Straw return is a promising strategy for managing soil organic carbon (SOC) and improving yield stability. However, the optimal straw return strategy for sustainable crop production in the wheat (Triticum aestivum L.)-cott on (Gossypium hirsutum L.) cropping system remains uncertain. The objective of this study was to quantify the longterm (10 years) impact of carbon (C) input on SOC sequestration, soil aggregation and crop yields in a wheat-cotton cropping system in the Yangtze River Valley, China. Five treatments were arranged with a single -factor randomized design as follows: no straw return (Control), return of wheat straw only (Wt), return of cotton straw only (Ct), return of 50% wheat and 50% cotton straw (Wh-Ch) and return of 100% wheat and 100% cotton straw (Wt-Ct). In comparison to the Control, the SOC content increased by 8.4 to 20.2% under straw return. A significant linear positive correlation between SOC sequestration and C input (1.42-7.19 Mg ha(-1) yr(-1)) (P<0.05) was detected. The percentages of aggregates of sizes >2 and 1-2 mm at the 0-20 cm soil depth were also significantly elevated under straw return, with the greatest increase of the aggregate stability in the Wt-Ct treatment (28.1%). The average wheat yields increased by 12.4-36.0% and cotton yields increased by 29.4-73.7%, and significantly linear positive correlations were also detected between C input and the yields of wheat and cotton. The average sustainable yield index (SYI) reached a maximum value of 0.69 when the C input was 7.08 Mg ha(-1) yr(-1), which was close to the maximum value (SYI of 0.69, C input of 7.19 Mg ha(-1) yr(-1)) in the Wt-Ct treatment. Overall, the return of both wheat and cotton straw was the best strategy for improving SOC sequestration, soil aggregation, yields and their sustainability in the wheat- cotton rotation system.