| In order to clarify the effects of nitrogen application rate on nitrogen utilization and grain yield under limited irrigation, field experiments were carried out during 2008-2009 in Gaocheng and Qingyuan with local commercial winter wheat cultivar Ji 5265 and Kenong 199, respectively. The experiments were all designed as randomized block arrangement, with the application rates of N 0, 120, 180, 240 and 300 kg·hm-2, respectively, indicated as N0, N120, N180, N240 and N300, respectively, under limited irrigations (three irrigations of 75 mm during the growing period). The results showed that, with the increase of nitrogen application amount, the contents and accumulation amounts of nitrogen in wheat plants and grains increased. The nitrogen accumulation in grain was all increased with the amount increasing of nitrogen application, with the accumulation amount of the treatment N300 was the highest in Gaocheng, but that of N240 was the highest in Qingyuan. The nitrogen dry matter production efficiencies decreased with the amount increasing of nitrogen application in both Gaocheng and Qingyuan. In Gaocheng's experiment, the grain production efficiency, recovery efficiency and agronomic efficiency of nitrogen all increased with the increase of nitrogen application amount, and reached the peak of nitrogen production efficiency for N180, and those of nitrogen recovery efficiency and agronomic efficiency for N240, then decreased. The spikes per hectare and grains per spike increased, but grain weight significantly decreased with the increase of nitrogen application amount. The grain yield also increased with the amount increasing of nitrogen application, although the difference in grain yield was statistically insignificant between N240 and N300. In Qingyuan's experiment, the dry matter production efficiency, grain production efficiency, recovery efficiency and agronomic efficiency of nitrogen were all decreased with the amount increasing of nitrogen application, and the difference among different treatments were significant. The highest values of spikes per hectare, grains per spike and grain yield were all achieved for N240, but the grain weight of N0 was the highest, and decreased with the increase of nitrogen application amount. According to the results, it is recommended that application of 240 kg·hm-2 N for satisfactory grain yield and nitrogen use efficiency of winter wheat under limited irrigation in Hebei Plain of China. |
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