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It was the basic for the management of soil nutrient and accurate, rational fertilization to understand temporal-spatial variability of topsoil nutrients and analyse the comprehensive evaluation of soil fertility. And it was of great significance to the sustainable development of agriculture. In this study, these two issues were the main lines, choosing Jingchuan County of Gansu Province as the research object. This paper explored temporal and spatial variability characteristics of topsoil pH and organic matter, total nitrogen, available phosphorus, potassium. Find the limiting factors that affected the variability of soil nutrients. Meanwhile, we combined AHP with membership functions of fuzzy evaluation method to complete the calculation of the integrated fertility index (IFI). Then, Jingchuan arable land was divided into five levels, and analyzed barriers and improvement measures for each grade arable land. The main findings were as follows:1, Descriptive statistical analysis of sampled datas after removing the outliers:the coefficient of variation (CV) of the pH value was2.22%, a weak variation; the coefficient of variation (CV) of the other4nutrients was in the range of19.62%to38.37%, a moderate intensity variation. The decreasing order of the coefficient of variation for5breeding was:AP> AK> OM> TN> pH.2、Sampled datas after being transformed by logarithmic were in line with the normal distribution. Using geostatistics software for spatial variability analysis, the block ratio of total nitrogen and available was not less or equal25%,which showed a strong spatial correlation, of the reason of soil parent material, climate and other structural factors; the block ratio of organic matter ranged from25%to75%, a moderate-intensity correlation, indicating that the impact of random factors and structural factors isroughly equaled; the block ratio of potassium and pH value was not greater or equal75%. which showed weak spatial correlation, of the main infectors of fertilization, tillage practices, cropping systems, and other random factors. The optimal model of organic matter was the spherical model; total nitrogen and phosphorus were the index model, pH, potassium were the linear model. 3^From the spatial interpolation results, the Kriging figures of organic matter, total nitrogen, available phosphorus showed that the nutrient content of eastern and northern in Jingchuan were relatively higher than others; the inverse distance weighted interpolation figure of potassium displays that AK content was patchy distribution and overall Jingchuan had a high content, an average of more than150mg/kg; the Kriging figure of pH value showed that the distribution was little, the basic value among8.0-8.6. slightly alkaline.4temporal variability analysis results of soil nutrients from1986to2008:pH value did not change scarcely, and other nutrient content have increased by varying degree. Such as soil organic matter increased31.54%, and the content of more than40%cultivated land area was basically up to the fourth level from the country fifth level; soil nitrogen increased41.19%,and the content was basically up to third or fourth levels from the country fifth level,. Soil available phosphorus increased70.90%, and the content was basically up to second or third level from the country fourth or fifth level. The available potassium increased26.64%, up to the first or second level from the country third or fourth level.5-. By dint of integrated fertility index fertility, the arable land of Jingchuan was divided into five levels. The area of the five classes arable land was4434.11hm2,10880.53hm2.18232.45hm2,4595.55hm2and2980.38hm2respectively, taking up10.78%.26.46%,44.34%,11.18%and7.25%respectively. The first and second levels were advised to use mulching and strengthen the construction of farmland water conservancy facilities to improve water use efficiency. It was also to increase organic fertilizer input.The third and fourth levels needed to strengthen farmland capital construction, construct level terrace, and throw rational fertilization. The last level was recommend to use reasonable crop rotation, if necessary, returning farmland to forest.
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