Organic Abstract of Red Rock Soil Crust in Arizona. Photo study by Minerva Bloom. Crusts contribute to a number of functions in the environment. Because they are concentrated in the top 1 to 4 mm of soil, they primarily effect processes that occur at the land surface or soil-air interface. These include soil stability and erosion, atmospheric nitrogen fixation, nutrient contributions to plants, soil-plant-water relations, infiltration, seedling germination, and plant growth. The lands where crusts occur is used for a wide range of purposes--from grazing and recreation to military uses, and in some places, crops. Ultimately, land managers need to know how the functions of crusts change under different practices. Where the functions of crusts are impaired or eliminated because of land use practices, and are essential to the health of the ecosystem, land managers need guidelines to adapt their practices to protect or restore the functions of crusts.