Study On Differences In Response Of Rice Genotypes To Nitrogen Fertilization And Nitrogen Use Efficiency

During the past half a century, all countries in the world took increasing nitrogen rate as an important agricultural measure to increase rice yield. It is an ideal approach for enhancing nitrogen use efficiency and reducing environmental pollution to explore and utilize crop's natural potential to screen N-efficient rice genotypes. A field experiment was carried out to study difference of response to nitrogen fertilization and nitrogen use efficiency of rice genotypes by using 115 rice genotypes as materials under 4 N levels including zero (0 N/666.7m2), low (10 N/666.7m2), medium (15 N/666.7m2) and high (20 N/666.7m2). Genotypic difference of growth period of difference rice genotypes was analyzed. Genotypes used in the experiment can be classified into 7 types. Difference of grain yield, characteristics of dry matter production and characteristics of nitrogen uptake and utilization of different growth type rice genotypes and their response to nitrogen were analyzed. Based on these results, evaluation and classification of nitrogen use efficiency were done. The main results were as follows:(1) There were all significant differences in growth period of rice genotypes under different N levels. The difference was least under zero N level and increased with increasing of N level. Whole growth period was prolonged significantly with increasing of N level as a whole, and the prolongation increased gradually. Seen from growth period structure, proper nitrogen application was advantaged to accelerate rice to head, but heading presented delaying tendency and days from heading date to maturing date prolonged gradually with increasing of N level. Seen from ratio of days during different growth period to whole growth period, ratio of days from sowing date to heading date to whole growth period decreased, while ratio of days from heading date to maturing date to whole growth period increased with increasing of N level.Based on the whole growth period under medium and Dingying's Standard of classificationof rice growth type, rice genotypes used in the experiment can be classified into seven type including early-maturing medium Japomca(EMMJ), medium-maturing medium Japonica (MMMJ), late-maturing medium Japonica(LMMJ), early-maturing late Japonica(EMLJ), medium-maturing late Japonica(MMLJ), medium-maturing medium Indica(MMMI) and late-maturing medium Indica(LMMI). Applying nitrogen prolonged whole growth period for all growth type rice genotypes, but there were significant difference in different growth types. The effect of nitrogen application on growth period increased with delaying of growth type. Compared with the same Japonica, days of nitrogen application to whole growth period of MMMI and LMMI were 0.5-1.7 d less than that of MMMJ and LMMJ.According to the response of early stage (from sowing to heading) and late stage (from heading to maturing) to nitrogen, rice genotypes used in the experiment under different N levels can be classified into three types including early stage shorten-late stage prolonged, early stage steadied- late stage prolonged and early stage prolonged-late stage prolonged.(2) There were all significant differences in grain yield of rice genotypes under different N levels. The difference was most under zero N level and decreased with increasing of N level. The effect of nitrogen on increasing grain yield decreased with increasing of N level.Rice grain yield increased under four N levels with delaying of growth type and presented a tendency of MMLJ>EMLJ>LMMJ>MMMJ>EMMJ. Between different subspecies of the same growth period, yield of Indica was higher than that of Japonica. Grain of MMMI was higher than that of MMMJ and grain of LMMI was higher than that of LMMJ under four N levels. Grain yield of MMM, LMMI and MMLJ under medium N level was highest with increasing of N level, while grain yield of EMLJ, LMMJ, MMMJ and EMMJ under high N level was highest with increasing of N level.By using grain yield as an index, cluster analyses were done of rice genotypes used in the experiment. Rice genotypes under four N...