Soil Conditions - Weed populations change in response to agricultural practices. The influence of weeds on soils and their use as indicators is described. Many tables and literature for further research. World Data Center for Soils - Is responsible for collecting, archiving, and distributing data and research information. The World Of Soil Forum - Online discussion of soil related issues.
Topics range from amateur to specialist.
World Soil Resources - The site provides maps, pictures, and technical information on global soil resources. The Worldwide Soil Jumpstation - Resources on soil, soil science, and soil management. Huge list of links. Intended for agriculture and horticulture.