OCR Text |
Show a foot will be satisfactory, although you can get various results with different heights. INTERPRETATION You will find that the water will rush off the bare soil into the fruit jar, taking soil with it. The flow will st6p soon, but the jar will contain muddy water. The water that flows from the sod will be reasonably clear. It will take longer for the flow to start and it will continue longer. Also, not as much water will reach the jar. The amount of water in the two samples before the experiment will affect the results somewhat. Unless the soils are waterlogged, however, the activity will be successful. The samples need not be completely dry. This activity illustrates one of the most fundamental principles of soil and water conservation- the protection grass gives soil against the pounding of raindrops and the movement of running water. The grass breaks the force of the raindrops so that the soil is not pounded and broken apart by this impact. The grass roots open up channels to let water get into the soil. Organic matter furnished by decayed grass crops also lets water Grass protects the soil and increases meat and dairy products. enter more readily, as we learned in Activity IX. And as the water runs off, the stems of grass slow it down so that it does not have enough speed to disturb the soil. Experiments show this is true. For example, on one plot at La Crosse, Wis., where corn had been grown every year for 6 years, the annual soil loss was 89 tons per acre. On a plot in blue- grass sod, however, the annual soil loss was only 0.2 ton per acre. XL How Does Mulch Prevent Soil Loss? Use the same boxes you made for Activity X. This time fill them both with the same kind of soil. Set them on the table as before, placing the sticks under one end to make a slope. Cover one box of soil with a thin layer of straw, grass, wood shavings, or sawdust; leave the other one bare. Sprinkle water on both boxes, using the same amount of water and pouring at the same rate from an equal height. Note how much and how fast water runs off into each fruit jar. Another way to study the protection of mulches on the soil is to drop water from a short height on soil that is not protected and on soil that is protected with a mulch. For this you will need two small tin cans. With an 8- penny nail, punch a hole in the bottom of each can and fill trie hole loosely with cotton. Put one- half inch of soil in two small fruit jars or water glasses. Put a light layer of dry grass clippings on one of the soil samples. Leave the other one bare. Arrange the tin cans so that they are about 4 feet above the jars of soil. Put about one- half inch of water in the cans. Large drops of water will form through the holes in the cans and drop on the soil in the jars. Note the amount of soil that is splashed on the sides of the glass. The third activity shows the effect of mulch on water intake of soil as well as the value of mulch in conserving soil and water. 13 |