样点数对县域土壤养分空间变异特征评价的影响

以广东省阳西县测土配方施肥耕地地力调查数据为基础,应用地统计学和GIS空间分析技术,对耕层土壤pH、有机质、全氮、有效磷和速效钾进行空间插值质量研究。结果表明:(1)土壤养分变异系数的顺序为速效钾>速效磷>有机质>全氮>pH,插值误差随土壤养分空间变异系数增大而增加。(2)插值精度随着插值样点数的增加而不断提高,土壤养分的预测值与实测值的相关系数逐渐增加。采样密度相同时,土壤养分的标准均方根误差(NRMSE)值由大到小的变化顺序是速效钾>有效磷>全氮>有机质>pH值。(3)对阳西县土壤养分空间变异情况进行评价时,土壤pH值和全氮采样时应以30～60 hm2耕地为一个采样单元;土壤有机质采样时应以20～30 hm2耕地为一个采样单元;土壤有效磷和速效钾采样时应最大以20 hm2耕地为一个采样单元。

Influence of sampling number on spatial prediction accuracy of soil fertility index at country scale

Based on the formulated fertilization survey data of Yangxi county of Guangdong province,spatial variability and accuracy of soil pH,organic matter,total nitrogen,available phosphorus and available potassium in surface soils were studied by using geostatistic and spatial analysis modules in ArcGIS.The results showed that:(1) The order of the coefficient of variation of soil nutrient was available potassium> available phosphorus>organic matter>total nitrogen>pH.The interpolation error increased with the increase of the spatial variability of soil nutrients.(2) The accuracy of the interpolation improved with the increase of soil sampling number,and the correlation coefficient between predicted and measured soil nutrients increased.The order of the Normalized Root Mean Square Error(NRMSE) value of soil nutrient with the same sampling density was available potassium> available phosphorus>organic matter>total nitrogen>pH.(3) The optimal area of sampling unit for soil pH and total nitrogen should be from 30 to 60 hm2,soil organic matter should be from 20 to 30 hm2,and available phosphorus and available potassium should be less than 20 hm2 when evaluating the spatial variability of soil nutrient in Yangxi county,