Carbon balance under four double-season cropping systems in North China Plain

Differences in cropping systems and their impacts on plant growth and carbon (C) uptake as well as soil C release pose a major challenge in projecting agroecosystem C balance. A four-year (2012-2015) field experiment was conducted to examine crop C uptake and soil respiration in two conventional (wheat-cotton and wheat-maize) and two legume-based (wheat-soybean and alfalfa-maize) double-season cropping systems in North China Plain. During the 4 experimental years, crop C uptake was greater in the two conventional systems than the two legume-based systems. However, soil respiration was higher in the two systems with C-4 (i.e. maize) than C-3 crops (i.e. cotton and soybean) planted in summer. As consequences, cropland C balance was positive in the two conventional cropping systems, with greater value in the wheat-maize comparing to wheat-cotton system. However, the two legume-based cropping systems showed negative cropland C balance. Our findings indicate that, although more CO2-C is emitted in maize-related cropping systems, the conventional agricultural activities may sequestrate more C in comparison with the legume-based farming in North China Plain due to higher C uptake, and highlight the importance of management strategy in improving agroecosystem C storage.