What Affects Aggregate Stability and How it is Managed

The stability of aggregates is affected by soil properties that change relatively little and by properties that change in response to changes in vegetation and management. As a result, measurements of the aggregate stability of a given soil should be compared only with measurements for the same or similar soils with similar textures.

Soil properties.—Soil properties that change relatively little include texture and type of clay. Expansion and contraction of clay particles as they become moist and then dry can shift and crack the soil mass and create or break apart aggregates. Calcium in the soil generally promotes aggregation, whereas sodium promotes dispersion. The quantity of calcium and sodium is specific to each type of soil.

Vegetation.—Management affects the plant community. Changes in the composition, distribution, and productivity of plant species affect aggregation-related soil properties, including aggregate stability, the amount and type of organic matter in the soil, and the composition and size of the soil biotic community. The amount of plant cover and the size of bare patches also are important. The centers of large bare spaces receive few inputs of organic matter and are susceptible to degradation.

Grazing.—Disturbance of the soil surface by grazing animals has both beneficial and detrimental effects on aggregate stability. It breaks the soil apart, exposing the organic matter “glues” to degradation and loss by erosion; however, it also can incorporate litter and standing dead vegetation into the soil, increasing the content of organic matter in the soil. Heavy grazing that significantly reduces plant production disrupts the formation of aggregates by reducing the inputs of organic matter. Grazing is more likely to increase aggregate stability in areas where an unusually large amount of standing dead material is on the soil surface and the risk of erosion is not increased by removal of plant material and disturbance of the soil surface.

You can improve the productivity of rangeland through good range management which normally increases aggregate stability. A few practices that you could use include:

• Maintain the optimum amount of live vegetation and litter
in order to maintain the content of organic matter and soil
structure and control erosion.
• Decrease the number and size of bare areas.
• Minimize soil surface disturbances, especially in arid

Try putting these practices into action on land that you have access too.