Reducing carbon footprint without compromising grain security through relaxing cropping rotation system in the North China Plain

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The North China Plain (NCP) is an important production base for wheat (Triticum aestivum L.) and maize (Zea mays L.) in China, but intensive continuous winter wheat and summer maize (WM) double-cropping system (control) has also created the high carbon footprint (CF) ecological problems. It is imperative to build a new rotation pattern that not only achieves direct and indirect low greenhouse gases (GHG) emissions, but also takes into account the grain security. CF metrics (per unit area (CFa), per unit economic output (CFe) and per unit kg grain yield (CFy)) were calculated for a two-year crop rotation experiment established at the Wuqiao Experimental Station, from October 2016 to September 2018. The treatments were eight alternative crop sequences grown in the first year, followed by WM in the second year. Alternative crop sequences included (1) WM, (2) fallow, (3) spring maize, (4) winter wheat, (5) spring sweet potato (Dioscorea esculenta (Lour.) Burkill), (6) spring peanut (Arachis hypogaea Linn.), (7) winter wheat-summer peanut, and (8) potato (Solanum tuberosum L.) - silage maize. The results showed that fallow → WM and winter wheat → WM were weak absorption sinks of net GHG, and other rotation patterns were all net sources during the experimental period, while the seven rotation patterns could attain 48%–94% of grain crops yield in control. Spring sweet potato → WM and winter wheat - summer peanut → WM, had no significant differences with control from three different CF perspectives. Spring maize → WM, spring peanut → WM, and potato - silage maize → WM produced more CF than control. Therefore, fallow and planting winter wheat alone in the first year of novel two-year rotation patterns reduced CF in the NCP, planting spring sweet potato and winter wheat-summer peanut increased net income without increasing CF and without compromising grain security, which could attain 1.53 and 1.12 times of the control. The research preliminary showed that winter wheat → WM, spring sweet potato → WM and winter wheat - summer peanut → WM were feasible to trade off of grain production and reducing CF.