Responses Of Canopy Nitrogen Distribution And Nitrogen Use Efficiency In Spring Wheat To Nitrogen Levels

Nitrogen is one of the main nutrients for crop growth, also an essential ele ment of photosynthesis. Photosynthesis is the material basis for the formation of crop yields, and improving the efficiency of photosynthesis is an important way to promote the efficiency of agricultural production. However, nitrogen fertilizer caused varying degrees of contamination on the environment while meeting crop nutrient needs and improving crop yields. So, a deeper understanding of canopy nitrogen regulatory mechanism and reasonable nitrogen application have great significance on improving nitrogen use efficiency and optimal management of resources in arid areas in crop production. To study growth stages of spring wheat canopy nitrogen distribution and response to nitrogen rates, response of leaf photosynthetic fluorescence characteristics, dry matter accumulation and yield components to nitrogen levels, three different drought resistance of spring wheat genotypes(Heshantou, Xihan 2 and N ingchun 4)were acted as experimental materials and five nitrogen levels(0kg·hm-2、75kg·hm-2、150kg·hm-2、225kg·hm-2、300kg·hm-2)were set in the field test conditions. The results showed that:1. Total nitrogen contents of the soil increased with nitrogen rate, it’s helpful to improve available nitrogen contents when topdressing fertilizer nitrogen in jointing stage. The demand for nitrogen of Heshangtou and N ingchun 4 are higher than Xihan 2 when vegetative growth turning to reproductive growth.2. Nitrogen application improved canopy height, increased specific leaf area, reduced leaf angle. Appropriate rate of nitrogen application(Heshangtou and Xihan 2 was 150 kg ? hm-2, Ningchun 4 225 kg ? hm-2) improved canopy total nitrogen content, increased its upper and middle gradient difference, the gradient difference between the middle and lower are different with each other because of genotypes, which caused by the difference of leaf angle and specific leaf area.3. Appropriate rate of nitrogen application(Heshangtou and Xihan 2 was 150 kg ? hm-2, N ingchun 4 225 kg ? hm-2) improved the conversion ratio of light energy to the photosynthetic carbon assimilation and ptotosynthetic rate, decreased the heat dissipation rate. Drought resistance cultivars had a higher Fv/Fm and ΦP SII, Nondrought resistance cultivar had a higher energy conversion efficiency(qp).4. Appropriate rate of nitrogen application(Heshangtou and Xihan 2 was 150 kg ? hm-2, Ningchun 4 225 kg ? hm-2) increased dry matter accumulation, effective ear number and 1000-grain weight. Excessive nitrogen fertilizer caused nitrogen metabolism, nutrition and reproductive growth disorders, inhibit ed transport of carbohydrate to grain. With the growth of the advance, the plant dry matter accumulation increased, the proportion spike biomass accumulation gradually increased, the proportion of stem and leaf biomass accumulation decreased.5. Appropriate rate of nitrogen application(0-225 kg ? hm-2) increased nitrogen accumulation of wheat, and that of Xihan 2 was the highest. N itrogen application decreased nitrogen harvest index and nitrogen production efficiency.The two drought resistance cultivars was significantly higher than N ingchun 4.