Performance of different cropping systems across precipitation gradient in North China Plain

Overuse of groundwater for irrigation under the current high yielding wheat-maize double cropping system has led to quick depletion of groundwater resources in North China Plain (NCP). Experimental work conducted for a relatively short period (several years) to explore water-saving cropping systems at limited sites offers useful, but limited insights regarding future sustainable cropping systems in NCP to balance productivity and groundwater usage. An understanding of the performance of various alternative cropping systems under the long-term inter-annual climate variability across the precipitation gradient in NCP is needed, but yet lacking. Our study provides a systematic assessment on productivity and environmental impact of 5 alternative cropping systems along a precipitation gradient across NCP, through combination of cropping systems modelling and scenario analysis. Our results show that the groundwater neutral cropping systems change from single summer maize, single spring maize, to wheat-maize double rotation from dry to wet areas across the precipitation gradient. Water restriction will inevitably lead to crop yield reduction (by 2-9 t/ha) and water saving depending on the choice of alternative cropping systems and location precipitation. Reduced water availability for irrigation will also reduce the amount of mineral nitrogen required and the associated N loss to the atmosphere and to the ground water. The reduction on N input was estimated to be 20-190 kg N/ha/year and N loss was 5-35 kg N/ha/year for the most productive cropping systems under rainfed conditions. A value for groundwater use is also estimated based on the extra grain yield produced with irrigation. The results provide the scientific basis for the design of future sustainable cropping systems, and future policies for water pricing and agricultural inputs (water and nitrogen).