Study On Spatial Variability And Site-specific Management Of Soil Nutrients Within Fields In Large Scale Operation System

Spatial unsynchronization of nutrient demand and supply was a key factor limiting crop yield and efficient utilization of nutrients. But at present, few researches have reported on spatial variability and site-specific management of soil nutrients in collective contract management system from the viewpoint of soil nutrients, crop yield and nutrient uptake, topography and other relative factors being systematically considered. In this research, a spring wheat production area of Keshan farm in collective contract management system in Heilongjiang province was chosen as the experimental area. Information technology such as geo-statistics, GIS and GPS were used to study spatial variability characteristics of soil nutrient, spatial relationship among soil nutrient contents, nutrient uptake amount of crop, crop yields and topography, and crop response to balanced fertilization in this study area. It can provide scientific bases to improve site-specific soil nutrient management techniques under collective contract management system suitable for our country status. The results are as follows:1. Spatial variability of soil nutrients in the spring wheat production area of Keshan Farm under the collective contract management system was described by using geo-statistics and traditional statistics. In this study area, soil nutrient limiting factors were N, P, K, S and Zn, and variation of soil nutrients differed obviously. Semi-variance structures of spherical or exponential model for spatial variability of soil OM,NO3--N,N and P existed this region. Patchy distribution of soil OM and nutrient contents was generally evaluated with relatively low contents in some areas, and relatively high contents in other areas of the study area.Spatial variability of soil OM was closely correlated with topography, and spatial variability of soil NO3--N was closely correlated with water content. Rainfall, agro-type and fertilization were thought to be the main factors influencing soil spatial variability.2. Based on the determined yields of spring wheat grain and straw and the collected samples in the three study areas, spatial variability of spring wheat grain yields and the spatial relationship among spring wheat grain yields, nutrient uptake amount of spring wheat and soil available nutrient contents were evaluated. Results also indicated that significant spatial variability of spring wheat grain yields was found in Keshan farm. Spatial variability of grain yields of spring wheat was closely correlated with soil OM, P, K, S and Zn contents while spatial variability of spring wheat straw yields was closely correlated with soil OM, P, K, S. Spatial variability of grain yields of spring wheat was closely correlated with uptake amount of N, P2O5 and K2O during growth period of spring wheat. Soil available nutrient was regarded as the most important source of crop nutrient uptake. Spatial variability of uptake amount of N and P7O5 during growth period of spring wheat was positively and closely correlated with soil corresponding available nutrient contents in soil before spring wheat seeding. The result also showed that spatial variability of spring wheat grain yields was closely correlated with 1000-grain weight and water content in soil before seeding, while spatial variability of spring wheat 1000-grain weight was closely correlated with soil P content prior to seeding.3. Field experiments were conducted to determine proper fertilizer application rates of spring wheat in Keshan Farm. The result showed that balanced fertilization promoted the growth, increased the yield and improved the quality of spring wheat. The optimum balanced fertilization formula was N 75 kg/hm2, P2O5 82.5 kg/hm2, K2O 52.5 kg/hm2, S 19.5 kg/hm2.Site-specific management techniques for high quality and high yield crop production were put forward based on the computerized fertilization recommendation system, the regionalized soil nutrient GIS maps and in this study area. Results from field experiments showed that site-specific management techniques were proper and optimized. Compared with farmer practice, site-specific balanced fertilization techniques increased grain yield spring wheat, income and N recovery rate by 8.1%～18.9%,455～520 RMB Yuan/ha and 3.0～6.2 percentage point, respectively.