Improving Yield and Water Productivity of Rainfed Summer Maize in Smallholder Farming: A Case Study in Hebei Province, China

Because of the strong competition for a limited resource of water and demand for food production, understanding yield and water productivity (WP) potentials and exploitable gaps in the current production of intensively rainfed maize (Zea mays L.) is essential on the regional scale in China. In this study, we conducted 411 site-year on-farm trials to assess the actual yield and WP of rainfed summer maize and its yield and WP potentials in Hebei Province, China. Each on-farm trial contained detailed information of three different treatments: no fertilizer application (CK), current farmers' practices (FP, depending on local farmer field fertilization management), and optimum fertilizer application (OPT, depending on soil testing and balanced fertilization). Results revealed that the yield and WP of rainfed summer maize in Hebei Province were 7635 kg ha(-1) and 20.7 kg ha(-1) mm(-1), respectively, and the yield and WP potentials were 12,148 kg ha(-1) and 32.0 kg ha(-1) mm(-1), respectively. Thus, the farmers attained 62.8% of the yield potential and 64.7% of the WP potential. A wide variation was observed in terms of the yield and WP across various types of farming. Compared with high-yield and high-WP (HYHW) farming, in low-yield and low-WP (LYLW) farming, the yield decreased by 24.9% and WP decreased by 44.4%. Nitrogen fertilizer application rate and rain were the most significant factors for yield and WP gaps among farmers, respectively. Other factors, such as solar radiation (tSola), soil available phosphorus content (AP), potassium fertilizer application rate, and grass-referenced evapotranspiration from planting to maturity (ET0), contributed the most to the variations in the yield and WP. Scenario analysis indicated that the optimization of fertilization levels from current to optimal for each farming could increase the yield and WP by 9.7% and 14.8%, respectively; closing gaps between the farming groups and achievement of the standard of HYHW farming by all farmers could increase the yield and WP by 14.8% and 35.5%, respectively; and achieving the yield and WP potentials could increase the yield and WP by 59.1% and 54.8%, respectively. These findings provided farming-based evidence that optimal nutrient management, advanced and climate-adapted agronomy practices, and higher soil fertility are essential for future maize production.