Carbon emissions in winter wheat – summer maize double cropping system under manure application and limited irrigation

Livestock manure is widely used for soil fertility improvement and land restoration in intensive cropping systems. However, annual carbon emission (CE) of intensified double cropping systems under manure application and limited irrigation has rarely been evaluated. Here, a 3-year field experiment was conducted to assess the effects of manure application (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc+m; and 100% manure N, Fm) and irrigation (without irrigation, W0; and with irrigation at wheat jointing stage, W1) on global warming potential (GWP) and CE in the North China Plain. The results show that soil CO2 emission contributed the main parts of total GWP and CE (i.e., 97.7% and 81.5%) under water-limited conditions. The irrigation regime W0 increased annual GWP by 21.9% and 11.1% in 2015–2016 and 2016–2017 than W1 (p < 0.05), respectively. The annual GWP and area-scaled CE (CEA) were both increased by manure application in 2015–2018 compared with Fc. Notably, the CEA of Fc+m and Fm was 17.0–34.9% higher (p < 0.05) than that of F0 in 2015–2018. The irrigation regime W1 reduced annual yield-scaled CE (CEY) by 8.6–18.2% than W0 due to increased annual grain yield. In contrast, manure application greatly increased annual CEA but had no impact on CEY compared to F0. The structural equation model (SEM) analysis indicated that CO2 emission is the main driver of CEY. In conclusion, the combined application of manure and chemical fertilizer, along with one additional irrigation, resulted in decreased CE and CEY when compared to manure alone. This implies that effective manure and irrigation management is essential for sustainable crop production, and innovative practices are desirable for climate mitigation under livestock manure application in agroecosystems.