Effects Of Nitrogen Fertilizer Application On Nitrogen Spatial-Temporal Distributions In Soil-Wheat System And Nitrogen Utilizition Efficiency In Wheat

Nitrogen fertilization is one of the most important measures to increase grain yield and improve grain quality in winter wheat. Unsuitable nitrogen fertilization often leads to lower income benefit and the larger accumulation of nitrate in soil, bring potential risk to environment. In order to explore the optional regime of nitrogen fertilizer application that suitable for environment and economy, a two year field experiment was carried out to study the effect of nitrogen fertilizer application on the temporal-spatial distribution and nitrogen utilization efficiency. The main results were summarized as follows:1. Effects of nitrogen fertilizer application on grain yield and nitrogen utilization efficiency (NUE) were studied. The results showed that grain yield was elevated remarkably by applying nitrogen fertilizers compared with treatment of NO, whereas, with an increase of N fertilizer rate, the NUE decreased. With appropriate rate of N fertilizer added, grain yield increased, but with application of excessive N fertilizer, grain yield would increase little, and even decreased. On the condition of the same rate of nitrogen fertilizer, increasing topdressing nitrogen rate clearly elevated grain yield and NUE markedly. There was no significant difference between Ningmai9 and Yumai34 in grain yield and nitrogen utilization efficiency. The correlation analysis showed that the grain yield was negatively related with NAE, NRE and NPE, but there were no significantly correlation between grain yield and NHI.2. Effects of nitrogen fertilizer application on soil nitrogen and apparent budget of soil N were studied. The results showed that alkali hydrolysable nitrogen (AHN) content in soil profiles was gradually decreased from surface soil layer to bottom soil layer, but there were significant difference in different treatment and wheat growth. NO₃^--N and NH₄⁺-N content was the highest before winter. NO₃^--N content of treatment with higher nitrogen rate at anther connective stage increased significantly with applying nitrogen fertilizer at jointing stage, while the treatment with lower nitrogen rate did not increase. At anthesis stage, NO₃^--N content of all Treatment increased because of applying nitrogen fertilizer at booting stage. Applying the nitrogen fertilizer at jointing and anthesis stage significantly increased NH₄⁺-N content in 0-20cm layers at anther connective and anthesis stage. The estimated results of ABSN indicated that it appeared soil N surplus in all fertilizer treatments from sowing to winter, but it appeared soil N deficit from winter to jointing. The fertilizer treatments with lower nitrogen rate appeared deficit from jointing to anthesis stage and from anthesis to maturity stage, while the fertilizer treatments with higher nitrogen rate appeared surplus.3. Effects of nitrogen application on uptake, distribution and utilization of nitrogen in winter wheat were studied. The results showed that the nitrogen accumulation was elevated by applying nitrogen fertilizers compared with treatment of NO, but with the application of excessive N fertilizer rate, the accumulation would increase little. From jointing to anthesis stage, the N accumulation and ratio of accumulation were all highest, so it was the peak period of N accumulation during the wheat growth. With the increase of N fertilizer rate, the proportion of N allocation to grain decreased, while the amount and proportion of N allocation to stem and leaf increased dramatically. Applying nitrogen promoted N accumulation in grain significantly. N fertilization also affected N transfer efficiency, which decreased with N rates increasing. The result also showed that the N fertilizer utilization efficiency decreased with the supplied N increased during the whole growth stage, but that in different growth stage existed difference. The NUE of base fertilizer was lower, while the NUE of topdressing was higer, so the base fertilizer should decrease and the topdressing fertilizer should be increased in the wheat cultivation.4. Temporal and spatial distribution of canopy nitrogen and its relationships with nitrogen utilization efficiency were studied. The results showed that the temporal distribution of nitrogen content in leaf, stem and sheath appeared consistency. The nitrogen content of leaf, stem and sheath with the treatment of NO was the highest on jointing stage, and then gradually decreased. Nitrogen content in leaf with the fertilizer treatment was the highest on connective stage, while the nitrogen content of stem and sheath was the highest on jointing stage, and then they all gradually decreased. The leaf nitrogen in two cultivars decreased with leaf layer lowering. There existed different vertical gradients of nitrogen among all treatments during growth stages. There was no apparent vertical gradient in stem and sheath in Ningmai9 compared with that of leaf in Yumai34. Plant nitrogen content increased with increasing nitrogen application rates, but reduced with growth processes. The correlation analysis showed that there existed difference between nitrogen vertical gradients in leaf and protein content of grain, and the third gradients of nitrogen were significantly negatively related with protein content. It also showed that nitrogen utilization in Ningmai9 was liable to be affected by the lower leaf on anthesis.