Effects of Long-Term Straw-Return Modes on Soil Organic Carbon Content and Carbon Footprint in Wheat–Maize Rotation System

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Straw return is widely applied in China to achieve sustainable grain production. However, inappropriate farm practices can increase greenhouse gas (GHG) emissions and reduce soil organic carbon (SOC) sequestration, thereby increasing the carbon footprint (CFP) and affecting soil fertility and climate change. A 10-year experiment was conducted to evaluate and quantify the effects of straw management on SOC, crop yield, and CFP under a winter wheat–summer maize rotation in the Guanzhong Plain. The experiment involved seven straw-return modes, namely high wheat stubble retention and chopped maize straw return (WH-MC), high wheat stubble retention and chopped maize straw return with sub-soiling every two years (WH-MM), high wheat stubble retention and no maize straw return (WH-MN), both chopped wheat and maize straw return (WC-MC), chopped wheat and maize straw return with sub-soiling every two years (WC-MM), chopped wheat straw return and no maize straw return (WC-MN), and a control with no return of either wheat or maize straw (WN-MN). The results indicate that SOC change, crop yield, and CFP were significantly influenced by the straw-return mode in the annual wheat–maize season. SOC sequestration rate was positively correlated with cumulative plant-derived C input, which ranged from 29.4 Mg C ha −1 in WN-MN to 100.7 Mg C ha −1 in WH-MC. Of all the studied treatments, WH-MC produced the highest grain yield and lowest CFP, which were 26% higher and 20.5% lower than those of the control, respectively. However, crop yield and CFP in the individual wheat or maize seasons were only slightly affected by straw-return mode; only WC-MN in the wheat season and WH-MC, WH-MM, and WC-MN in the maize season produced a significantly higher grain yield and lower CFP compared to the no straw return treatment. Annual GHG emissions were highest in the WC-MM treatment and lowest in WH-MN. Therefore, WH-MC found to be the most suitable straw-return for lowering CFP and enhancing crop yield and SOC sequestration. However, to achieve the coordinated development of agriculture and the livestock industry it is necessary to remove some straw for animal feed and fuel, so WH-MN produced optimum yield and maintained SOC stock with low GHG emissions.