Factors Continued...Soil Properties

Soil Properties

Soil texture (proportion of clay, silt, and sand particles in a soil) has two effects on soil erosion. The first is in its influence on infiltration or entry of water into the soil. When rainfall infiltrates rapidly, runoff is minimal. For example sandy textured soils have large pores acting like large pipes that allow much of the rainfall to soak right into the soil. Sandy soils are known to have good infiltration and drainage. Clay textured soil have small pores more like narrow pipes that do not allow water to soak into the soil fast. Clay soils are known to have poor infiltration and drainage.

Second, particles vary in their ease of detachment. Silt particles are most easily detached because they are small and do not easily form aggregates.

**Image by NASA Globe program** https://www.globe.gov/

Aggregation

Particles of fine sand, silt and clay may join together to form aggregates. The soil property which describes the character and formation of these aggregates is called soil structure. The glue that joins the soil particles together includes organic matter, clays, iron oxides, aluminum oxides, and lime. Aggregate formation in clay-textured soil improves water infiltration into the soil and drainage because it increases the number of large pores (larger pipes). In sandy textured soil, aggregate formation reduces the excessively fast drainage of water by increasing the number of small pores (narrow pipes).

Aggregates

Can be described by their grade. The grade is a measure of how well the aggregate is cemented together or, conversely, how easily it is broken down by the impact of water, wind, or human activity. A soil with good structure has many aggregates present which are stable, meaning well cemented together. Such aggregates resist the forces of water, wind, and human activity. Consequently, they can maintain their porosity and allow better water and air movement.

Soil Moisture

Moist soils are less prone to wind erosion due to the cohesive or binding effects of water on soil clay and organic matter. As wind dries the soil, the risk of soil loss erosion by wind increases, especially if aggregate grades are weak. The risk peaks at or below permanent wilting point.

Quiz

Question

What soil textural class is expected to have a low rate of water infiltration? Why? What can be done to improve the water infiltration rates of soil?

Response

Fine or clay textured soil would have a low rate of water infiltration. Since the pores or empty spaces between these small particles are small, they do not allow water to enter as fast. Addition of organic matter would enhance aggregation of these fine sized soil particles. The gluing or aggregation of small clay particles creates some larger particles that have larger pores or empty spaces in between. Thus, the infiltration rate would be increased.

Looks Good! Fine or clay textured soil would have a low rate of water infiltration. Since the pores or empty spaces between these small particles are small, they do not allow water to enter as fast. Addition of organic matter would enhance aggregation of these fine sized soil particles. The gluing or aggregation of small clay particles creates some larger particles that have larger pores or empty spaces in between. Thus, the infiltration rate would be increased.

Question

What change(s) in soil can cause soil to have low rate of water infiltration? How might these changes come about?

Response

1) Compaction (reduces the amount of pores or empty spaces) due to traffic on the soil surface; 2) Excess salt from fertilizers, groundwater seepage, or poor quality irrigation water, disperses soil particles. Soil particles then plug the pores or empty spaces; 3) Erosion by wind or water removes the surface soil rich in organic matter and leaves behind a thick clay soil that has low infiltration rate.

Looks Good! 1) Compaction (reduces the amount of pores or empty spaces) due to traffic on the soil surface; 2) Excess salt from fertilizers, groundwater seepage, or poor quality irrigation water, disperses soil particles. Soil particles then plug the pores or empty spaces; 3) Erosion by wind or water removes the surface soil rich in organic matter and leaves behind a thick clay soil that has low infiltration rate.