| Nitrogen is macroelement that are essential for high yield and quality. A substantial increase in cotton production is based on high input of nitrogen. But nitrogen use efficiency of cotton is currently low, typically 30%-40%, which caused resources waste and environmental pollution. Optimum nitrogen rate increase the cotton yield and improve quality, enhance nitrogen use efficiency, and reduce excessive pollution caused by nitrogen.In this study, we carried out field experiment to study the effects of nirtogen appliction rate (Nitrogen control,0 kg N·hm-2; optimum nitrogen,240 kg N·hm-2; excessive nitrogen, 480 kg N·hm-2) on cotton growth, soil nutrient characteristics and soil enzyme activity in U.S. cotton 33B (NUCOTN 33B) and Cotton Division One (Kemian 1). The study focused on the:(1) Effect of nitrogen application rates on cotton growth and yield at different growth stages in cotton. (2) Effect of nitrogen application rate on soil nutrient characteristics and spatial and temporal variability. (3) Effect of nitrogen application rates on soil enzyme activity and soil nutrient.The main results are as follows:1. Different nitrogen rates on yield characteristics and dry matter accumulation and portion. Nitrogen promotes the Fruit branches, leafs and root dry matter accumulation.2. Different nitrogen rates affects soil enzyme activities in different cotton growth stages. (1) Nitrogen increase the soil Urease,invertase and alkaline phosphatase enzyme activity in the depth of 0-20cm soil layer. Urease, invertase activity reached maximum activity in blooming period, The activity of alkaline phosphatase, catalase reached the highest in boll opening stage. Respectively:19.96%,8.03%,29.55%. (2)Coefficient of variation of activity of urease, alkaline phosphatase, catalase was small, invertase is higher. (3) The activity of urease, alkaline phosphatase, catalase was significantly correlated in each soil layer.3. Different nitrogen rates on temporal and spatial variation of soil nutrient and soil enzyme. (1) Optimum nitrogen can improve the soil nitrogen, potassium, phosphorus and other available nutrient content in depth of 0-20cm. Trends of soil available nutrients for the seedling stage to flowering stage increased lower than boll stage. (2) Nitrogen content and urease activity have a strong positive correlation. The highest value of nitrogen content occurred later than the activity of urease. Available phosphorus and soil alkaline phosphatase activity were significantly or very significantly positively correlated. Alkaline phosphatase activity showed significant or highly significant positive correlation with soil available K. Urease activity and soil organic matter, total nitrogen, available phosphorus, potassium and pH values were highly significant positive correlation. (3) Optimum nitrogen rate (240 kg N·hm-2) improve the soil nutrient content and quality of fiber, increase nitrogen use efficiency. (4) We can provide a theoretical nitrogen rate(240 kg N·hm-2) on in Xuzhou. |
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