Human Land-Use and Soil Change

Soil change refers to the alteration of soil and soil properties over time in one location, as opposed to soil variability across space. Although soils change through natural processes (pedogenesis), this chapter focuses on human-caused soil change. Soil change can occur with human land use and management over long or short time periods and small or large scales. While change can be negative or positive, often soil change is observed when short-term or narrow goals overshadow soil’s other ecosystem services. Assessing soil change depends upon the ecosystem services and soil functions being evaluated. The interaction of soil properties with the type and intensity of management and disturbance determines the changes that will be observed. Many soils have been changed in their chemical, physical, or biological properties through agricultural activities, including cultivation, tillage, weeding, terracing, subsoiling, deep plowing, manure and fertilizer addition, liming, draining, and irrigation. Tillage of cropland disrupts aggregates and decreases soil organic carbon content, which can lead to decreased infiltration, increased erosion, and reduced biological function. Improved agricultural management systems can increase soil functions including crop productivity and sustainability. Forest management is most intensive during harvesting and seedling establishment. Most active management in forests causes disturbance of the soil surface, which may include loss of forest floor organic materials, increases in bulk density , and increased risk of erosion. In grazing lands, pasture management often includes periods of biological, chemical, and physical disturbance in addition to the grazing management imposed on rangelands. Grazing animals have both direct and indirect impacts on soil change. Hoof action can lead to the disturbance of biological crusts and other surface features impairing the soil’s physical, biological, and hydrological functions. There are clear feedbacks between vegetative systems and soil properties; when vegetation is altered because of grazing or other disturbances, soil property changes often follow. Some soils are very sensitive to management and disturbance and can undergo rapid change; for example, cropping led to massive gully formation in the southeastern USA, exposure of acid sulfate soils leads to irreversible changes in soil mineralogy, and thawing of cold soils has created thermokarst features. These soil changes alter soil properties and functions and may impact soil ecosystem services far into the future.