Healthy Soil

Healthy Soil is Productive Soil - The Health of South Dakota Cropland Soils

Soil organic matter greatly influences the chemical and physical characteristics of soils and in turn affects crop productivity.  Several soil characteristics impacted by the amount of organic matter present in the soil are aggregate stability, soil tilth, infiltration rate, runoff, nutrient holding capacity, and the amount of nitrogen available through mineralization.  Currently, the majority of cropland in South Dakota presently has only 50-60 percent of the soil organic matter originally present in the native prairie soils.  The rate at which organic matter is lost is very dependent on the crop rotation, amount of crop residue returned to the soil, amount of rainfall received, temperature, soil moisture, and soil management factors such as tillage.

Tillage in crop production promotes organic matter decomposition which releases nitrogen for use in crop production.  Conventional tillage systems in rotations such as wheat-fallow promote this decomposition.  Wheat-fallow rotations account for two million acres, or 13 percent, of the cropland resource in South Dakota.  This culture of growing one crop in two years, coupled with frequent tillage operations in the fallow year to control weeds, decreases soils aggregate size through the frequent tillage and stimulates oxidation of the organic matter.  As a result of this organic matter depletion, soil tilth is degraded so that the window of time for proper tillage operations is reduced and in turn the planting time for more diverse rotations is limited.  This problem is especially true for soils derived from Pierre shale as well as other soils in the state that have a heavy textured surface.  The reduction in soil tilth also contributes to other associated problems such as soil compaction.  At the present time, compaction may result in yield reduction on 10-20 percent of the cropland acres in South Dakota.  This is especially true during periods of abnormally high rainfall.  In addition, conventional fallow systems often allow water, nitrates, and other salts to move below the root zone.