Agricultural practices (C and P factors)

These two photos are of agricultural lands in Iowa. Which one has more evidence of soil erosion? Why?

These images illustrate the impact that conservation practices can have on soil erosion rates in agricultural lands. Terracing (creating a series of "steps" on steep slopes), stripcropping (alternating different crops in a single field), and contouring (planting rows along the contour of the hill), as shown in the image on the right, are common conservation practices that can help significantly reduce soil erosion in agricultural landscapes. The effectiveness of these practices can be explained by considering how water moves through a landscape. In the image on the left, water can flow freely downhill, taking soil particles with it. The conservation practices employed in the other image impede the flow of water, slowing it down giving it less erosive power. The impact of these practices are reflected in the support practices factor, abbreviated by the letter "P". These practices are big scale investments and typically don't change on a regular basis.

Cropping and management decisions made on a regular basis have the most potential to significantly impact soil erosion on agricultural lands. These practices affect the ability of rainfall to erode the soil by determining a number of characteristics. Canopy (cover from the plants themselves) protects soil from the impact of raindrops. Surface cover (such as mulch) also absorbs the energy from raindrops and slows down surface runoff. Below-ground biomass (biomass in the soil from roots and incorporation of crop residue through tillage) holds the soil together and increases soil organic matter. Prior land use and existing soil moisture can also contribute to the erodibility of the soil. Taken together, the effects of management practices on the soil are reflected in the cover-management factor, abbreviated by the letter "C". The RUSLE allows for calculation of the impact of these practices on soil erosion and can be used in the development of a conservation plan for a specific field.

Resources

• Renard, K. G., Foster, G. R., Weesies, G. A., and Porter, J. P., 1991, RUSLE - Revised Universal Soil Loss Equation: Journal of Soil and Water Conservation, v. 46, no. 1, p. 30-33.
• Renard, K. G., Foster, G. R., Weesies, G. A., McCool, D. K., and Yoder, D. C., 1997, Predicting Soil Erosion by Water: A guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE), USDA Agricultural Research Service Agriculture Handbook Number 703, 384 p.
• RULSE: On-line Soil Erosion Assessment Tool