Characteristics And Control Of Nitrogen Mineralization In The Farmland Soils Of Erhai Lake Basin

The mineralization of organic N is a very important process in soils, which becomes a main resource of soil N supplying by transforming the organic N that is hard to be utilized to inorganic N that could be directly used by plants. However, once the mineralization is excessively strong, it will cause plenty of N to enter the Waters by means of runoff or leaching, which may lead to water eutrophication and a series of environmental problems. So to learn about the characteristics and the regulation of mineralization of N in soil is crucial to fertilization and environmental protection. In this paper we selected the soils in farmland of Erhai Lake basin as our study object which was located in Yunnan Province. By long-term and short-term aerobic incubation experiment and C/N regulation experiment of exogenous additives in lab, we studied the mineralization process and its influencing factors of N in soils under different using types of farmland, and also the mineralization parameters were determined by modulation of mineralization potential of N using one-pool model; then the influences of organic manures of different C/N mixed with inorganic N fertilized were analyzed and the correlation between mineral N and microbial biomass N was further discussed.The nitrogen mineralization in soils of farmland in Erhai Lake basin was relatively strong, and the mineralization of samples during two weeks differed a lot, also the average mineralization was 65.54 mg·kg^-1,which was mainly composed of NO₃^--N. The rank of nitrogen mineralization during two weeks was vegetable fields>cereal fields>garlic fields, while the average value of vegetable fields and cereal fields were significantly higher than that of garlic fields, also the change trend of mineralization rate accords with mineralization value. During the long-term experiment, weekly mineralization value and rate of N were decreasing with incubation time at first, then tending to be stable after ten weeks, however, accumulative N mineralized showed an opposite trend with mineralization value and rate of N, which means a increasing trend with time. Only at first cultural stage the mineralization value of vegetable fields and cereal fields were significantly higher than that of garlic fields, at other times, the three showed insignificant difference. During 119 days, in surface layer of the soil the average accumulative mineralization of N in vegetable fields, cereal fields and garlic fields were 172.49 mg·kg^-1,178.25 mg·kg^-1and 159.63 mg·kg^-1, so the rank was vegetable fields > cereal fields > garlic fields.The weekly mineralization of N and accumulative N decreased with soil layers deepening. The mineralization of N between 0²0cm and 20⁴0cm was relatively similar with each other, so the difference between the two layers was far less than that between 20⁴0cm between 40⁶0cm. Also the differences of accumulative mineralization of N among layers increased with prolonged cultural time.In short-term experiment, the mineralization N in soil showed positive correlation with organics and total N in an extremely significant way, while a negative correlation with pH in an extremely significant way. During the long-term incubation, the correlation coefficient between mineralization of N and total N showed consistent trend with that between mineralization of N and organics, with the former one higher than the latter one, also the correlation coefficients was increasing with time; while during the early time the mineralization of N showed negative correlation with pH in a significant way, then turning to be weak with time. The accumulative mineralization of N showed negative correlation with pH at early stage, however it showed significantly positive correlation with total N and organic matter. And it showed linear and logarithmic correlation with the square root of incubation time.By using one-pool model to simulate the mineralized process in soils in Erhai Lake basin, the effect was relatively good with a high goodness-of-fit. The mineralization potential of N showed positive correlation with total N and organics; the constant of mineralized rate(k) showed negative correlation with total N, organics and pH in an extremely significant way.The influence of additives to N in soil showed a certain important relationship. The content of mineral N in soils mixed fertilized with both organic manures and mineral N was higher than that in soils fertilized with only organic manures, and it decreased with increasing C/N of organic manures, while the content of mineral treatment and the blank treatment was different, the former one was between hog manure and cattle manure with mineral N, and the latter one was between hog manure and cattle manure. Organic manures of high C/N fertilized together with inorganic N can reduce the content of inorganic N under inorganic N treatment, while organic manures of low C/N fertilized together with inorganic N can increase the content of inorganic N under inorganic N treatment. Organic manures with high C/N can reduce the content of inorganic N in soils, while organic manures of low C/N can increase the content of inorganic N in soil.