Soil_Types__USDA_

This Soil Types feature layer was obtained from USDA and their Soil Survey. The USDA Natural Resources Conservation Service website provides the following definition of Soil Survey: “The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. (ii) The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors…” Soil surveys commonly identify the more important soil characteristics that determine the limitations and qualities of the soil. These were once published in book form for individual counties by the National Cooperative Soil Survey, and are now freely accessible to the public on NRCS’ Web Soil Survey (WSS).

本土壤类型要素图层来源于美国农业部（United States Department of Agriculture, USDA）及其土壤调查项目。美国农业部自然资源保护局（USDA Natural Resources Conservation Service）官网对土壤调查给出如下定义：“地球表层的未固结矿物或有机物质，可作为陆生植物生长的天然介质。(ii) 地球表层存在的未固结矿物或有机质，曾受遗传与环境因子作用并体现出相应影响……” 土壤调查通常会识别出决定土壤质量与限制性特征的关键土壤属性。此类调查成果曾由全国合作土壤调查（National Cooperative Soil Survey）以单县分册的图书形式发布，如今可通过美国农业部自然资源保护局的网络土壤调查系统（Web Soil Survey, WSS）向公众免费获取。