A handful of soil can contain millions of different nematodes, bacteria, protozoa, and other organisms. Soil is a critical part of a well-functioning ecosystem, recycling nutrients to plants which become food for animals and humans. The quality of its soils determines whether a community can grow enough food to support its population, so soil is one of the most important and most vulnerable natural resources. Modern farming methods, including irrigation, heavy use of machinery, and fertilizers have substantially increased the yield of agricultural products, but they can contribute to deteriorating soil quality. Soil can be compacted by the use of heavy farming machinery, making it less permeable to water, which can exacerbate runoff and erosion.
Intensive cultivation can lead to loss of soil nutrients.
Changes in land use can have a rapid effect on soil quality. Deforestation can cause erosion, in which the layers of soil most suitable for farming are washed away. In dry areas, irrigation that is not properly managed can cause an accumulation of salts that severely degrades soil quality. Soils Originally called the Soil Erosion Service, this U.S. Department of Agriculture agency was established by Congress after the devastating destruction in the area of the Dust Bowl. Their site provides access to major national soil information databases, keys to taxonomies for classifying soil, and the geographic distribution of soil types.