Incorporating the WHCNS model to assess water and nitrogen footprint of alternative cropping systems for grain production in the North China Plain

Abstract

Water shortage and reactive N (Nr) release from excessive fertilization are major challenges for sustainable grain production in the North China Plain (NCP). Alternative cropping systems in this region must be explored because traditional winter wheat and summer maize (WW-SM) rotation is maintained at the cost of high consumption of irrigation water and N loss to the environment. In this study, a soil–crop system model (WHCNS, soil water heat carbon and N simulator) and a life cycle assessment were integrated to analyze and evaluate water footprint (WF) and N footprint (NF) for alternative cropping systems of wheat and maize (2H1Y_FP, two harvests in 1 year with farmer’s practice; 2H1Y_RI, two harvests in 1 year with reduced inputs; 1H1Y, one harvest in 1 year with reduced inputs; and 3H2Y, three harvests in 2 years with reduced inputs) in the NCP. Results showed that NH3 volatilization and NO3− leaching are the main hot spots of NF for different crops. For the composition of WF, blue and green WF contributed largely to the total WF of wheat and maize, respectively, and the proportion of gray WF for maize could be decreased by 30% with the reduction in fertilizer amount. The yearly average NF (kg N-eq t−1 y−1) showed the following order: 1H1Y (2.65) <3H2Y (3.41) <2H1Y_RI (6.15) <2H1Y_FP (17.46), and the yearly average WF (m3 t−1 y−1) showed the same order as follows: 1H1Y (565.22) <3H2Y (830.15) <2H1Y_RI (1162.19) <2H1Y_FP (1633.18). Among the compared cropping systems, the 1H1Y and 3H2Y modes as potential alternatives to traditional WW-SM cropping systems showed advantages of sustaining groundwater exploitation and mitigating groundwater nitrate contamination in the NCP. However, the two modes compromised 33%–37% and 20%–25% of crop yield in comparison with those of 2H1Y systems. By considering the site-specific climate and soil conditions, the WHCNS model-based WF and NF analyses could serve as an accurate and effective tool for screening various cropping systems in clean agricultural production.