soil and vegetation
Overview When vegetation covers an area, the soil tends to be cooler and more moist than in a similar area with no cover. Organic matter that builds up gives the soil a more porous texture that allows water to percolate through it rather than running off. Vegetation also tends to keep the soil temperature cooler. In turn, forests benefit from relatively stable soil temperature and moisture levels. Objectives To show the difference between soil that has roots and organic matter in it and soil that is bare, when it comes to absorption of water. Soil that has been baked dry does not readily absorb water, and causes faster run-off with more erosion. Less organic matter (and thus generally less nutrients) will be observed in dry soils exposed to the sun. Procedure On a warm, sunny day, in spring or fall when there is grass growing, find a slope nearby that faces the sun at midday. Look for an area that has grass or low ground cover and a similar area that has been tracked down, for example a path, with bare dirt. Spray or pour water from a hose or can onto the top of each area, letting the water run down slope. Note the differences in the way the run-off behaves, and the different amounts of earth movement in each case. Optionally, in an adjacent dry spot, use a thermometer to measure the ground temperature on the bare earth or covered area. Place the thermometer on the ground and then shade it from the direct rays of the sun. In both cases try to determine the temperature of the earth (you may have to spread the grass or ground cover apart to get the thermometer against the ground). See if there is a difference in temperature. References/Links Use the Threats to Forests and Soil sections of this site for background information. Encyclopedias and other references can be used to research desertification.
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