In-Season Root-Zone Nitrogen Management Strategies for Improving Nitrogen Use Efficiency in High-Yielding Maize Production in China

Many recently developed N management strategies have been extremely successful in improving N use efficiency. However, attempts to further increase grain yields have had limited success. Field experiments were conducted in 2007 and 2008 at four sites to evaluate the effect of an in-season root-zone N management strategy on maize (Zea mays L.). According to the in-season root-zone N management, the optimal N rate (ONR) was determined by subtracting measured soil mineral N (NH+4−N and NO−3-N) in the root zone from N target values. Other treatments included a control without N fertilization, 70% of ONR, 130% of ONR, and recommended N rate (RNR) by agronomists in China that have been shown to approach maize yield potentials. Although apparent N recovery for the ONR treatment was significantly higher than that under RNR in 2007, grain yield declined from 13.3 to 11.0 Mg ha−1 because of an underestimation of N uptake. In 2008, N target values were adjusted to match crop uptake, and N fertilization rates were reduced from 450 kg N ha−1 for RNR to 225 to 265 kg N ha−1 for ONR. High maize yields were maintained at 12.6 to 13.5 Mg ha−1, which were twice the yield from typical farmers' practice. As a result, apparent N recovery increased from 29% to 66%, and estimated N losses decreased significantly for the ONR treatment compared to the RNR treatment. In conclusion, the in-season root-zone N management approach was able to achieve high yields, high NUE and low N losses.