Nitrogen recommendation for winter wheat using Nmin test and rapid plant tests in North China Plain

Nitrogen (N) over-fertilization is a common phenomenon in cereal crop production in North China Plain in order to meet the food requirement by increasing population. It is of significance to optimize N fertilization in winter wheat according to crop N need using suitable N recommendation methods. Thus a field experiment with split-plot design was carried out in this region to evaluate the role of N-min (mineral N) test and rapid plant tests on N recommendation for winter wheat. The results showed that N-min sollwert (NS, N-min +fertilizer N) 90 kg N ha(-1) at regreening stage (early March) and N rate 90 kg N ha(-1) at shooting stage (middle April) could meet N requirement of winter wheat with the target yield of 6000 kg ha(-1). Plant nitrate concentration in the stem base of wheat as well as SPAD readings (using SPAD-502 chlorophyll meter from Minolta, Japan) of wheat functional leaves positively correlated with the NS levels at shooting stage, indicating that plant nitrate and SPAD tests could reflect the N nutritional status at this stage. Under treatment of NS 90+90, the 0-90 cm soil residual N-min (53.2 kg N ha(-1)) and apparent N loss (12.4 kg N ha(-1)) were controlled at the environmental safe levels without yield loss compared with other treatments with higher N rates, suggesting total N supply of 180 kg N ha(-1) may be the optimal fertilization under the experimental condition.