在不同尺度下宁夏引黄灌区农田土壤养分空间变异分析

Spatial Variability of Soil Nutrients at Different Sampling Scales in Farmland in the Yellow River Irrigated Area in Ningxia

以宁夏引黄灌区农田土壤为研究对象，在10m和1m两种尺度上网格取样，共取耕层土壤样品（0—20cm）223个，利用经典统计和地统计相结合的方法，对土壤全氮（TN）、全磷（TP）和pH的空间变异性进行研究。经典统计表明两种尺度下pH的变异系数（CV）均为0．02，属弱变异，其尺度效应不明显。随着采样尺度的减小，TN的CV减小，TP的CV增大，二者具有明显的尺度效应。地统计分析表明，两种尺度下TN、TP表现出中等或强烈的空间相关性，其空间分布受结构和随机因素的共同影响。受灌溉、施肥等随机因素影响，1m尺度上的pH在空间上呈弱相关性。各向异性分析表明，两种尺度下3种土壤元素都有一定程度的各向异性，且在东北方向空间变异性较强。交互验证的结果表明，克里格插值的平均误差接近0，均方根误差接近1，可以准确反映两种尺度下土壤养分的空间分布状况，说明宁夏引黄灌区农田土壤养分存在一定的尺度效应和各向异性。

The study on spatial variability of soil nutrients in farmland plays an important role in controlling the regional agricultural non-point source pollution and implementing the precision agriculture. Topsoil samples （0 - 20 cm） were collected from 223 sites in farmland at two scales of sampling grid （ 1 m x 1 m and 10 m x 10 m） in the Yellow River Irrigated Area in Ningxia Hui Autonomous Region, China. The objectives of this study were to in- vestigate the spatial variability of total nitrogen content （TN）, total phosphorus content （TP） and pH value at the two sampling scales using the conventional and geostatistical means. The conventional statistical analyses showed that the coefficient of variability （CV） of pH value was 0.02 and in a slight spatial variability, which indicated that the scale effect was not obvious. With the decrease of the sampling scales, the CV value of TN decreased but that of TP increased. The effects of scales were significant for TP and TN. Geostatistical analyses showed that there was a moderate or high spatial correlation between TP and TN at the two sampling scales, and their spatial distribution was jointly affected by structural and random factors. There was a weak spatial correlation of pH value at the 1 m x 1 m scale due to the effects of random factors, such as irrigation and fertilization. There was a certain anisotropic effect of TN, TP and pH value at the 2 scales, and also a high spatial variability northeastward. The cross-valida- tion showed that the average error of Kriging interpolation was close to 0, and the error of mean square root was close to 1. The interpolation figures could be used to accurately reflect the spatial distribution of soil nutrients. The research results indicated that there was a certain scale effect and also an anisotropy effect for soil nutrients in the Yellow River Irrigated Area.