Critical Nitrogen Curve and Nitrogen Nutrition Index for Spring Maize in North-East China

The study was conducted at three sites during 2008 and 2009 in the North-East China Plain(NECP). Field experiments consisted of five or six nitrogen (N) fertilization rates (0–350 kg N ha−1). Shoot biomass and N concentration (Nc) of spring maize (Zea mays L.) were determined on six sampling dates during the growing season. Nitrogen application rate had a significant effect on aerial biomass accumulation and Nc. As expected, shoot Nc declined during the growing
period. A critical N dilution curve (Nc = 36.5 W−0.48) was determined in China, which was a little different from those reported for maize in France and Germany. Besides, the N nutrition index (NNI) calculated from this critical N dilution curve was significantly related to relative grain yield, which can be expressed by a linear with plateau model (R2 = 0.66; P < 0.001). NNI can be used as a reliable indicator of the level of N deficiency during the growing season of maize.