Research On The Law Of Organic Nitrogen Mineralization And Its Regulation Measures Of Tobacco Soil In Hunan

In order to solve the technical problems such as tobacco soil nitrogen mineralization, critical control measurements on improving soil nitrogen supplying and quality of tobacco leaves, and establishing the water-fertilizer and coverage model of tobacco soil organic nitrogen regulation et al., the law of tobacco soil organic nitrogen mineralization and the impact factors and control measurements were analyzed in Liuyang and Sangzhih where the typical tobacco planting area in Hunan province. The main findings and results were as follows:The process of tobacco soil organic N mineralization was different due to the diferent climate and soil properties. In Liuyang tobacco soil, the amount of N mineralization was small in the six weeks before transplanting, but increased sharply after six weeks of transplanting, and then decreasing after the peak during8to10weeks. However, in Sangzhi, the amount of N mineralization maintained at a relatively stabled level during the whole life cycle of the tobacco. Nitrate N was mainly mineralized up to more than90%during the process of tobacco soil N mineralization, and the important reason of excessive total N and nicotine content of upper leaves was the excessively N mineralized that resulted in the highly up-taking in the late growth period of tobacco.Temperature and humidity were the key factors affecting the soil organic N mineralization. Within the normal range of temperature in tobacco planting area, the speed of N mineralization and the amount of N accumulation was increased with the increasing temperature, while higher than15℃, the mineralization rate was significantly accelerated. The mineralized N accumulation was increased followed by the increased soil water content, while high water content could reduce the N accumulation. Results in this study indicated that tobacco soil N mineralization and mineralized N accumulation was in the highest level when the soil water content at0.25g·kg-1(v/v), therefore, improving the soil temperature and maintaining the soil water content with a proper level is benefit to accelerate the soil organic N mineralization.Soil N mineralization and mineralization rate was increased in the condition of Nitrogen and Carbon supplying. Reduced the soil C/N proportion and applied the fast-decomposable C could increase soil C/N proportion that is conducive to the prompt start of the pre-soil N mineralization. The soil fertility property was more significant affected when changed soil C/N proportion in a short period, and the up-taking of N, P, and K of tobacco plant was increased and with increased accumulation as well. Therefore, reduce soil C/N ratio would reduce nitrogen use efficiency result in the nitrogen fertilizer loss; both the fast-decomposed and blunt-decomposed C fertilizer could improve soil C/N ratio and nitrogen use efficiency, while the blunt-decomposed C fertilizer also able to reduce the nitrogen loss.N mineralization process quickly started after mulching with a significant increased in soil N mineralization rate, the amount of pre-mineralization, strengthened N mineralization strengthen and increased in total soil N mineralization. The earlier of ridging, fertilization and mulching, the more benefit for soil organic N mineralization and soil mineralized N release in advance, the more benefit to N uptake and consumption for tobacco, therefore, the more benefit to reduce N supplying and ensuring normal maturation of tobacco and excess up-taking in the late growth period.N mineralization peak in the35-55d when ridge-fertilize-mulch at25d-45d before transplanting, which was relatively in line with the tobacco N absorption law. At the same nitrogen level, advance in mulching, tobacco biomass increased with a peak at45d after transplanting, and ridging and mulching in advance also conducive to the improvement of nitrogen use efficiency. At the expecting of yield and quality of tobacco, advance in ridging and mulching might be appropriate to reduce the amount of nitrogen fertilizer. This study also shown that, advance in mulching in25d, the yield and quality of tobacco leaves relatively coordinated with90kg/hm2of nitrogen application.Uncover the mulch instead of rice straw could effectively increase the fresh and dry weight biomass of tobacco plant and the available part of the leaf, and there was a positive correlation between the amount of rice straw and tobacco biomass. Yield, output, and upper-middle grad tobacco leaves proportion, especially in the upper grad tobacco proportion increased significantly when applied rice straw with350kg-667m2, among which the combined effect of increased yield and quality was the best. Moreover, each treatment with rice straw mulching, the content of N, P, and K of upper layer of tobacco soil increased slightly after harvesting. While, rice straw mulching treatment increased the nicotine and total nitrogen content of the upper leaves to some extent.In this study, the water-fertilizer and mulching management profile for high quality tobacco production was established under the integration of all measures of tobacco soil nitrogen regulation. According to this profile, yield and output of tobacco production, compared with the control treatment,21.84kg and247.11Yuan was increased, and the upper-grad tobacco leaves proportion increased by9.14%and2.62%in upper-middle grad tobacco leaves, while the nicotine content of the upper leaves decreased by8.48%. Hence, water-fertilizer and mulching management mode has positive significance to improve the yield, quality and output of tobacco production.