| 4 Effect of Nitrogen Fertilization and Different Soil Moisture Conservation on Wheat Yield and Soil Fertility Tutor: Professor Li Shengxiu Ph. D. Student: Xu FuIi Summary Dryland farming has played very important roles in agricultural production of our country. It is need to effectively solve the main existing problem in dryland area, such as low soil fertility and water stress, and keeping stable and sustainable development. It抯 very important to study nitrogen fertilization techniques for winter wheat and measures of soil moisture conservation. The research results will supply the valuable materials and information for further development of dryland agriculture and protection nature resources. In this thesis the field experiments were carried out and lasted 4 years.To investigate the effects of fertilization on dryland area, and soil moisture conservation methods on growth, development and yields of winter wheat etc, In irrigated area the nitrogen application rates and applying time were studied through field experiment. One simulation experiment was also made for evaluating the feasibility of the EUF method for assesses the mineralization ability of the plants traced with ?N in the soil. The major conclusions obtained from the experiments are as follows: 1. Study on the mineralization ability of the plants traced with 15N in the soil with EUF Method The rape seedling labeled with ?N was applied into the soil and the aerobic incubation was conducted. The electro-ultrafiltration (EUF) techniques were used to extract the mineralized inorganic nitrogen (ammonium and nitrate) and organic nitrogen (EUF-Norg) in different culture periods, and the ?N in the extracted solution was analyzed using isotopic techniques. The results showed for the undisturbed soil its nitrogen mineralization model is Y=7.2+O.4 IT, and nitrogen mineralization model of the rape seedlings labeled with ?N is Y~4.6+O.43T. During the early 40 days?of aerobic incubation, 38% of organic nitrogen existing in fresh plants(rape seedlings) was mineralized, there after the mineralization process kept stable. The isotopic analysis results demonstrated that the EUF extraction percentage is 7 times higher than that unlabeled organic nitrogen, from easily mineralization plants with ?N labeled in the soil. This showed that easily mineralized nitrogen by extracted with EUF method could easily absorbed by plants, and organic nitrogen extracted by EUF Method can de thought to be available for plants. When soil nitrogen supplying capacity is determined, the contributions of these organic nitrogen to crop nitrogen absorption must be considered. 2. Study on nitrogen fertilizer requirement and fertilizer application time for winter wheat 5 in irrigated area 2.1 Nitrogen fertilizer application experiment showed owing to a large amount of nitrogen fertilizer has been applied years by years, the response of wheat growth and yield formation to nitrogen fertilizer is not sensitive. The effect of yield increase is not obvious. When the nitrogen application rate is 50 kg N/jim2, the nitrogen utilization efficiency is 19.0 %~~4].0oo; When nitrogen application rate is 150 kg N/jim2, either fertilization in autumn or in spring the nitrogen utilizati... |
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