Page 274 - Nutrient Management Planning Guide

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Factors Affecting Runoff Nutrient Losses

more info

For information on the soil temperature issue in direct seeding systems, consult the following resource, available from the AF Publications Office (1-800-292-5697) or search by Agdex number on Ropin the Web.

Froebel, B. and Howard, •

A. 1999. Soil temperature and direct seeding. AF. Agdex 590-2.

Provided by Andy Jedrych, AF

Figure 8.1.4 Predicted Runoff Volume (measured as runoff depth as a function of slope grade for slopes 50 m, 200 m and 500 m in length). From data generated for a WEPP simulation for a loam textured soil in central Alberta climatic conditions.

The volume of runoff from a site increases with increased grade and increased length of slope. An increase in the grade of the slope increases the gravitational force on water and, depending on soil factors (i.e., permeability, texture, etc.), may increase its tendency to flow along the surface rather than infiltrate into the soil. The relationship between runoff and soil/nutrient loss is illustrated in Figure 8.1.5.

Generally, the longer and steeper the slope the greater the sediment loss will be (Figure 8.1.5). In addition, soil loss is a function of soil texture, land use (e.g., crop type and stage, tillage regime) and climatic conditions. The energy of the water to detach sediment particles from the soil surface increases as the volume and intensity of the runoff increases.

Provided by Andy Jedrych, AF

Figure 8.1.5 Predicted Surface Soil Loss, kg/m 2 as a Function of Slope Grade (for slopes 50 m, 200 m and 500 m in length). From data generated for a WEPP simulation for a loam textured soil in central Alberta climatic conditions.

Vegetation or Ground Cover

Many erosion control measures provide ground cover to protect the soil. It is particularly useful if ground cover is maintained high-risk periods such as during snowmelt runoff. Ground cover limits runoff by providing a physical barrier, which also increases the chance for runoff to infiltrate. Vegetative cover also serves as a filter to increase the removal of particles from runoff. Ground cover can be present in the form of living plants or as residue from the previous crop (Figure 8.1.6).

Vegetation and ground cover have several important effects on rainfall and runoff water: