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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 (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.
Many recently developed N management strategies have been extremely successful in improving N use efficiency. How-ever, attempts to further increase grain yield 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 for an underestimation of N uptake. In 2008, N target values were adjusted to match crop uptake, and N fertilization ra testified 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.