Increased nitrogen use efficiencies as a key mitigation alternative to reduce nitrate leaching in north china plain

The Northern China Plain (NCP) produces over 20% of the national grain production. Best management practices (BMP) for intensive irrigated cropping systems of the NCP are based on large nitrogen (N) applications without accounting for N budgets. There are concerns that non-scientific based BMPs may be impacting underground water resources. We conducted the first study in this region, located at the Luancheng Experimental Research Station that measured the effects of N fertilizer rates on nitrate-nitrogen (NO3-N) leaching losses. From October 1, 2001 to September 30, 2004, we used a water balance approach with a neutron probe, weighing lysimeter, and suction cups located at 1.8 m depths on a winter wheat (Triticum aestivum L.)–corn (Zea mays L.) rotation to monitor NO3-N leaching. Residual soil NO3-N, yields, and N uptake by aboveground biomass were also measured. Corn received two surface broadcast applications every year of 50, 100, 150 and 200 kg urea-N ha−1 for the N200, N400, N600, and N800 treatments, respectively. The first broadcast application was at seeding and the second at tassel. Similarly, winter wheat received two surface broadcast applications, initially as a pre-plant and a second application at the jointing stage of growth in spring. We monitored NO3-N leaching losses for the N200, N400, and N800 treatments. Average NO3-N leaching losses during wheat–corn season were 6, 58, and 149 kg NO3-N ha−1 year−1 for the 200, 400, and 800 kg N ha−1 year−1 treatments, respectively. The NO3-N leaching increased with N applications (P < 0.05) and were in agreement with the NO3-N concentrations of 12, 74, and 223 mg NO3-N L−1 for soil water at 1.8 m depths for the 200, 400, and 800 kg N ha−1 year−1 treatments, respectively. Higher than needed N fertilizer applications increased the NO3-N leaching losses and reduced the N use efficiency (NUE) without yield increases. We propose that there is a need for a new scientifically based BMP approach for the NCP based on N budgets that credits soil NO3-N before planting, N mineralization from soil organic matter, and other potential N sources as a key mitigation alternative to increase NUE and reduce NO3-N leaching in this region.