Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/14/2006
Publication Date: 2/2/2007
Citation: Li, X., Hu, C., Zhang, Y., Delgado, J.A., Ouyand, Z. 2007. Increased nitrogen use efficiencies as a key mitigation alternative to reduce nitrate leaching in the northern china plain. Agricultural Water Management. 89:137-147. Interpretive Summary: Our study is the first to use suction cups to assess NO3-N leaching under different N rates for the Northern China Plain (NCP). Our soil profile data, soil water NO3-N concentrations at 1.8 m depths collected with suction cups, and our water and balance to calculate drainage and NO3-N leaching losses are in agreement. This shows that excessive N fertilizer rates will contribute to accumulate large amounts of NO3-N in the soil profile, to over 600 kg NO3-N ha-1 on the top 1.5 m. Additionally, excessive N fertilizer rates will contribute to large N losses to the environment, with NO3-N leaching losses of up to 150 kg NO3-N ha-1 y-1. There is the need for a program to be established to help farmers use an N balance approach based on N from mineralization of organic matter initial soil NO3-N as well as N fertilizer inputs to cut the NO3-N leaching losses that are impacting underground water resources across the NCP. Additionally, if we cut the N inputs, the pathways for other N losses will also be reduced (Delgado, 2002). There is also the need to test new tools such as the Delgado et al. (2006) N Index based on the framework presented by Shaffer and Delgado (2002) or modeling to assess the N management across the NCP region. The principles for managing NO3-N leaching, as reported from Meisinger and Delgado (2002), need to be considered to synchronize N applications with N sinks. There is great potential to significantly increase the N use efficiencies across the NCP, however this should be done based on a scientific approach that considers N budgets for sustainable maximum yields while maximizing N use efficiencies. This data shows that for management practices that have similar yields, the management practices that increase a CSANUE provides information on the potential to cut back N applications without reducing yields.
Technical Abstract: The Northern China Plain (NCP) produces over twenty percent of the national grain production. Nitrogen (N) best management practices (BMP) for intensive irrigated cropping systems of the NCP are based on large 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 1st, 2001 to September 30th, 2004, we used a water balance approach with a neutron probe, weighing lysimeter, and suction cups located at 1.8 m depths on 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. Average NO3-N leaching losses were 6, 58, and 149 kg NO3-N ha-1 y-1 for the 200, 400, and 800 kg N ha-1 y-1 treatments, respectively. The NO3-N leaching increased with N applications (P<0.05) and were in agreement with the 4, 75, and 216 mg NO3-N L-1 for soil water at 1.8 m depths for the 200, 400 and 800 kg N ha-1 y-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 give credits to 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.