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. How- ever, 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 （NHa＋-N and NO3-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.