Approximately 65 percent of the earth’s soils are degraded to some extent. The primary causes are overgrazing, removal of vegetation, and agricultural practices. When land is overgrazed or deforested or when crops are harvested, there is often not enough plant litter remaining to protect and nourish the soil. Soil organisms die, resulting in a loss of fertility. Sparse cover allows raindrops to erode the surface, loosening the soil’s structure, freeing up fine clay particles, and transporting them downhill. Repeated mechanical tilling changes the structure of the soil so it erodes more easily, and compaction by heavy farm equipment reduces water infiltration and increases runoff. Nutrients are also lost when farmers fail to allow fallow periods or to replenish the soil.