Livestock or crop? Which deserves more investment to reduce greywater footprint emissions and improve water use efficiency?

There are two distinct directions of agricultural development when considering only crops and livestock. They are integrated crops and livestock systems (ICLS) and separated crops and livestock systems (SCLS). When evaluating agricultural greywater footprint (GWF), nitrogen cycling and nitrogen fixation in ICLS reduce nitrogen emissions always neglected. A novel study that aims to efficiently use water and reduce water pollution in agriculture to guide investment between crops and livestock is appealing. Based on the panel data of 11 provinces in the Yangtze River Economic Zone from 2007 to 2018, we employ the slacks-based model to evaluate agricultural water use efficiency (AWUE). GWF plays an unexpected output in the model. Furthermore, we compare both AWUE and GWF between ICLS and SCLS. The results show: (i) ICLS produce approximately 4.76 million cubic meters GWF less than SCLS, 1.89% of total GWF emission of SCLS. The greywater footprint emissions of the province’s unit-mass meat (GWFM) increased by an average of 26.30%. By contrast, the greywater footprint emissions of unit-mass grains (GWFG) decreased by an average of 27.37%. (ii) ICLS improves the AWUE of the province to the highest level of 10.78% compared with SCLS. (iii) If government allocates capital investment in crops and livestock freely, an additional 1% of crops investment would increase by 1.94% of GWFG while livestock could reduce GWFG by 2.12%. Investment in livestock is valid.