The objectives of this research was to find out the present situation of soil available nutrients in the major grain-producing farmlands in Xi ’ an 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 Chang ’ an District , Hu County and Zhouzhi County in Xi ’ an 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 nutrients is 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 N is 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 .%耕层土壤速效养分现状是区域平衡施肥、耕地保养和农业生产的基础。本研究选取西安市辖的长安区、户县和周至县的农业区，综合运用统计学、地统计学和GIS技术，结合“3414”田间试验结果，研究耕层土壤速效氮、磷和钾的空间变异特征，丰缺格局及其影响因子。结果表明，当前耕层土壤速效氮、磷和钾平均含量分别为59.06 mg/kg、21.26 mg/kg、127.66 mg/kg，比值介于1∶1∶25∶1∶15，空间含量分布主要呈东西向趋势，表现出明显的城乡过渡特征。在样点间距约500 m的采样尺度下，土壤速效养分的块金系数介于0.5330.710，均表现出中等强度的空间相关性，空间变异性是由地形地貌、土壤类型、质地等自然因素和施肥、灌溉等人为因素共同作用的结果。整体上，土壤速效钾含量丰富；速效磷较丰富，仅1.14％耕地缺乏；速效氮普遍不高，50.78％的耕地缺乏。盲目施肥和养分利用率低是农业生产的主要障碍因素。今后的生产实践中应密切关注钾的消耗、氮的补充和磷肥的控制，平衡土壤养分，提升区域经济和生态效益。
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