Quantifying water footprint of winter wheat-summer maize cropping system under manure application and limited irrigation: An integrated approach

Recycling of livestock manure in agroecosystems can promote resource utilization and reduce negative environmental consequences from intensive crop-livestock systems. However, the interaction effect of manure application and irrigation strategy on the water footprint (WF) of crop production still remains incomplete. Here, we estimated the WF of the winter wheat - summer maize cropping system based on a three-year field experiment under limited irrigation and manure application by combining the hydrological water balance and the life cycle assessment. Four fertilization strategies were chemical fertilizer (Fc), manure (Fm), the combination of chemical fertilizer and manure (Fc+m), and no fertilizer input (F0). Two irrigation regimes were irrigation (W1) and no irrigation (W0) at the jointing stage of wheat. W1 increased the blue WF (groundwater consumption per unit of grain yield) of the wheat-maize system by 46-95% compared to W0. The annual blue WF of Fm was 6% lower than that of Fc+m under W0 in 2016-2017, while that of Fc+m was lowest under W1 in 2016-2017 and 2017-2018. Fm had a higher annual yield under W0, while Fc+m yielded better under W1. Notably, the combination of limited irrigation and manure application decreased annual blue WF by benefitting annual grain yield through improving soil water storage. The indirect water consumption per unit grain yield of Fc+m and Fm were 57% and 17% of Fc for wheat and maize, respectively. Our findings highlight the great reductions in blue water footprint and indirect water consumption through limited irrigation and manure application, suggesting an effective way to balance freshwater conservation and crop production.