Spatial characteristics of soil available nutrients in the major grain-producing region of Xi’an,  China

The objectives of this research were to find out the present situation of soil available nutrients in the major grain-producing farmlands in Xian City, Shaanxi Province, which is the theoretical basis for the balanced fertilization, farmland fertility maintenance and efficient agricultural production. Based on the GIS technology and taking the agricultural regions of Changan District, Hu County and Zhouzhi County in Xian City as the research area, the spatial variability, supplying availability and the main influencing factors of soil available N, P and K were analyzed using statistics and geostatistics combined with the results of 3414 experiments. The average contents of soil available N, P and K are 59.06 mg/kg, 21.26 mg/kg and 127.66 mg/kg with the N:P:K ratio ranging from 1:1:2 to 5:1:15, showing obvious urban-rural transition trends (East-West direction). Under 500 m sampling scale, the nugget to sill ratios of the available nutrientsare 0.533-0.710, in the range of moderate spatial dependence. The nutrient spatial variability is affected not only by natural factors including topography, geography, soil types and textures, but also by human activities such as fertilization and irrigation. In the area studied, soil available K is abundant as a whole, P and Nare lack in 1.14% and 50.78% of farmland respectively. Not scientific fertilization and induced low N efficiencies are the main obstacles in the grain production.