Straw incorporation increases crop yield and soil organic carbon sequestration but varies under different natural conditions and farming practices in China: a system analysis

Abstract. Loss of soil organic carbon (SOC) from agricultural soils is a key indicator of soil degradation associated with reductions in net primary productivity in crop production systems worldwide. Simple technical and locally appropriate solutions are required for farmers to increase SOC and to improve cropland management. In the last 30 years, straw incorporation has gradually been implemented across China in the context of agricultural intensification and rural livelihood improvement. A meta-analysis of data published before the end of 2016 was undertaken to investigate the effects of straw incorporation on crop production and SOC sequestration. The results of 68 experimental studies throughout China in different edaphic, climate regions and under different farming regimes were analyzed. Compared with straw removal, straw incorporation significantly sequestered SOC (0￢ﾀﾓ20￢ﾀﾉcm depth) at the rate of 0.35 (range 0.31￢ﾀﾓ0.40)￢ﾀﾉMg C￢ﾀﾉha￢ﾈﾒ1￢ﾀﾉyr￢ﾈﾒ1, increased crop grain yield by 13.4￢ﾀﾉ% (range 9.3￢ﾀﾉ%￢ﾀﾓ18.4￢ﾀﾉ%) and had a conversion efficiency of the applied straw-C as 16￢ﾀﾉ%￢ﾀﾉￂﾱ￢ﾀﾉ2￢ﾀﾉ% across the whole of China. The combined straw incorporation at the rate of 3￢ﾀﾉMg C￢ﾀﾉha￢ﾈﾒ1￢ﾀﾉyr￢ﾈﾒ1 with mineral fertilizer of 200￢ﾀﾓ400￢ﾀﾉkg N￢ﾀﾉha￢ﾈﾒ1￢ﾀﾉyr￢ﾈﾒ1 was demonstrated to be the best combination for farmers to use with crop yield increased by 32.7￢ﾀﾉ% (range 17.9￢ﾀﾉ%￢ﾀﾓ56.4￢ﾀﾉ%) and SOC sequestrated by the rate of 0.85 (range 0.54￢ﾀﾓ1.15)￢ﾀﾉMg C￢ﾀﾉha￢ﾈﾒ1￢ﾀﾉyr￢ﾈﾒ1. Straw incorporation achieved higher SOC sequestration rate and crop yield increment when applied to clay soils, under high cropping intensities, and in areas like Northeast China where the soil is being degraded. SOC responses were the greatest in the initial starting phase of straw incorporation and then declined and finally were negligible after 28￢ﾀﾓ62 years, however, crop yield responses were initially low and then increased reaching their highest level at 11￢ﾀﾓ15 years after straw incorporation. Overall, our study confirmed that straw incorporation did create a positive feedback loop of SOC enhancement together with increased crop production, and this is of great practical significance to straw management as agricultural intensifies in China and other regions in the world with different climate conditions.