[Effects of nitrogen fertilization rate and harvest time on summer maize grain yield and its quality].

In order to approach the optimal nitrogen fertilization rate and suitable harvest time for the high grain yield and quality of summer maize in Huanghe-Haihe Area, a field experiment with five nitrogen fertilization rates (0, 113, 181, 249, and 375 kg N x hm(-2)) and two harvest time (S1: September 23, conventional harvest time for local farmers, and S2: September 29, 6 days delayed) was conducted. The results showed that the kernel number, grain yield, and 1000-grain mass increased with nitrogen fertilization rate, but the differences were not significant. With increasing nitrogen fertilization rate, the protein and lysine contents of the grains increased, while the starch content decreased. After 6 days delayed for harvest, the grain yield, 1000-grain mass, and the starch and lysine contents of the grains increased, but the protein and crude fat contents decreased. Based on the yield level, the optimal nitrogen fertilization rate for the summer maize in Huanghe-Haihe Area was 113-180 kg N x hm(-2), and the suitable harvest time was from September 29 to October 5.