| Variable-rate fertilization is one of the key technologies in precision farming. In this dissertation, different topics related to variable-rate fertilization prescription were studied. Soil sampling strategies and yield data processing technologies were analyzed and studied, the influence of management zone size on variable-rate fertilization was studied theoretically, and DSS for variable-rate fertilization precision was also designed and implemented. According to the experiment, these results can provide support for variable-rate fertilization implementation. The main results are as follows:1. Soil nutrients in the same locations are statistically related to each other and spatially related. Both spatial variability and traditional statistics need to be considered in sampling and interpolation of soil nutrients. N/S value and CV are good indicators of spatial variability and traditional statistics. Soil EC is a compositive indicator of soil physical-chemical properties and can show the productivity of farmland to certain extent. Veris 3100 EC Meter is a type of quick and cheap equipment for acquirement of soil system information.2. The acquisition process of yield data was studied, and the principle of AHP (Analytic Hierarchy Process) was applied to systematically classify factors leading to yield data errors into direct and indirect factors. Five types of filters were designed and realized to deal with different error sources in yield data, including yield limits filter, harvester speed filter, filling and cleaning delay filter, neighbor mean filter, and neighbor coefficient filter. Based on analysis of different filters, a synthesized filter was provided to filter outliers in yield data for acquirement of reliable yield map.3. The influence of management zone size on variable-rate fertilization under different soil fertilities was studied. Field distribution dataset series of soil nitrate concentration in 500X500m2 field were generated based on given values of mean, standard deviation and related distance. Each dataset is composed of nitrate concentration values in 104 cells, with the unit cell size of 5x5 m2. The fertilization rate was calculated using the fertilization models established by D.W. Franzen and L.J. Cihacek in North Dakota based on a common potential yield and the mean value hi each management cell size. The yield was calculated based on combination of fertilization amount and soil nitrate storage in each location with the same yield potential. Based on the fertilization rate and yield, the NUE (nitrogen use efficiency, yield increment with unit weight of fertilizer) was calculated. The result shows increasing or constant fertilization rate, increasing yield and NUE when the size of management zone for variable rate fertilization decreased. When the soil fertility increased, the fertilization rate decreased and the yield and NUE increased. As the management zone for variable rate fertilization becomes larger, the difference of the fertilization rate, yield and NUE between different soil fertility levels becomes more significant With the increase of standard deviation, the increment of the fertilization rate from large management zone size to small management size scale 1 to 100 become quicker, the difference of yield between different soil fertility levels at the same management zone size become larger, and the difference of the NUE between different soil fertility levels at the same management zone size become smaller.4. Based on analysis of variable rate fertilization decision-making process, OLE/ActiveX technologies were applied to integrated GPS, GIS, ES and MS into decision support system, which has the functions of navigation for sampling, yield map processing, decision support function, and variable-rate fertilization prescription. Analytic component of model expression was embedded into the inference engine. The OLE and automation made it possible for inter-operation between the system and GIS functional components. Knowledge, models,...
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