不同取样方式下土壤质地空间插值的精度分析
Error analysis of spatial interpolation of soil texture under different sampling schemes
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摘要: 为研究土壤质地的合理取样方式, 进而研究其空间变异情况, 为田间施肥及灌溉提供依据, 本试验利用地统计学方法和GIS技术, 在重庆市彭水县重庆烟草试验站, 利用289个表层土样, 研究了16 m间距的栅格取样法(对照, 253个土样, 扣除36个验证样点)、34 m间距的栅格取样法(115个土样)和随机取样法(115个土样)3种取样方式下土壤质地的空间插值精度。3种土壤颗粒指标中粉粒占68.43%, 砂粒含量最少, 占12.68%, 黏粒含量略高于砂粒。砂粒和黏粒具有中等强度的变异性, 粉粒具弱变异性, 且数据符合正态分布。地统计分析显示, 在分析该区域土壤质地时, 采用栅格取样方法应适当增大取样间距, 而采用随机取样方法可适当缩小取样间距。交叉检验显示, 土壤质地成分在3种取样方式下的插值精度均以对照最大, 栅格取样次之, 随机取样最小。综合考虑插值误差、样品采集和分析成本及时效性等因素, 本研究建议在该区域进行土壤质地空间变异规律分析为生产服务时应采用随机取样。Abstract: Soil texture is a qualitative classification tool used in both the field and laboratory to determine the classes of agricultural soils based on physical texture. Surface soil texture reflects soil physical and chemical properties, which affects not only soil fertility and farming/production performance but also crop quality and yield. Precision agriculture requires reliable data on the variations in field soil properties for effective management decisions. The most common way to do this is to predict the values for un-sampled places using observed samples and represent the variations in maps. The optimal sampling method is importation in the evaluation of spatial variations in soil texture, which is more critical for fertilization or irrigation in precision agriculture. The acquisition of precise soil data which are representative of an entire survey area is critical for irrigation and fertilization in precision agriculture. Here, we compared the ability of three sampling methods used in estimating the precision agriculture practices and predict the spatial distribution of soil texture with the goal of choosing the optimal sampling method. About 289 soil samples were collected from the field at 0 20 cm depth in 16 m grid cells in the Southeast Pengshui County of Chongqing City. The geostatistics method and Geographic Information System (GIS) was used to evaluate the accuracy of the 16 m grid-cell sampling (a total of 253 sampling points), 32 m grid-cell sampling (a total of 115 sampling points) and random sampling (a total of 115 sampling points). The results showed that the largest component of the soil texture was silt and the lowest was sand. While sand and clay exhibited a medium variation, silt showed a low variation. Based on Kolmogorov-Smirnov test, sand, silt and clay were all normally distributed. Results of geostatistics analysis suggested that larger sampling intervals were needed under grid-cell sampling while lower sampling intervals could be used under random sampling of spatial variability of soil texture in the study area. Cross validation showed that the interpolation precision was highest for soil texture components under experimental control (16 m grid-cell sampling). This was followed by 32 m grid-cell sampling, while then random sampling had the lowest interpolation precision. The research indicated that based on the factors considered (including interpolation precision, cost effectiveness and timeliness), random sampling was the optimal method for analyzing soil texture in the study area.