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Show to the ground line above the fence and measure from it to the ground. 3. Measure the growth of a gully. Find one that is cutting deeper and farther into the field with each rain. Drive wooden pegs 10 to 15 feet above the gully head and on each side of the gully ( see drawing). After each rain, measure from each stake to the nearest edge of the gully to see how much the gully has grown. Do this after several rains and compare your measurements to see how much the gully has grown since you first set the stakes. By measuring the width, depth, and length of the gully, figure out how many cubic feet of soil have been lost. INTERPRETATION Soil washed from a field is not necessarily lost forever. But for all practical purposes it may be lost for a very long time. The soil that fills the bottom of a lake, for example, is still soil, but it is useless for agriculture. Soil that is piled deeply at the lower edge of a field covers other soil, making it useless. And soil that is carried to the sea may lie there, turn to rock, and later be raised from the ocean floor by geologic action to be broken down again into soil. The first person to suffer from loss of soil usually, though not always, is the farmer. Many experiments have shown that in general the deeper the original topsoil the higher the yield of crops. In Missouri topsoil 12 inches thick produced 64 bushels of corn per acre while top- soil 4 inches deep produced 38 bushels. The soils were side by side and received the same treatment. In Washington, wheat yielded 35 bushels per acre on topsoil 11 inches deep, but only 23 bushels on topsoil 5 inches deep. So the farmer loses when he loses topsoil. His crop yields go down. The cost of producing each bushel of grain or pound of meat goes up. And, he makes less money or even loses money. People who do not live on the land depend on the farmer to grow their food. The surplus that he grows becomes their three meals a day. Actually, whole civilizations depend on this surplus. The primary producers- the farmers- must supply a surplus of food, clothing, shelter, and other necessities before the artisans, engineers, scientists, philosophers, writers, and others can live. Few nations ever advanced their civilization while all their people produced their own food, clothing, and shelter directly from the soil. We can find plenty of evidence that countries that lost their ability to produce a surplus actually lost their civilizations too. All across the continent of Asia and into Europe and North Africa, for example, you can find centers of former civilizations that are now among the backward areas of the world. It is true that conquering hordes that repeatedly overran these countries sacked and razed the cities. But where soil and other resources remained the cities were usually rebuilt. It was only after the land was depleted or exhausted that the fields became barren and the cities were not rebuilt. How badly has erosion hurt America ? According to the best information we now have, millions of acres once cultivated have been converted to other uses because of damage caused by erosion. And according to latest surveys, erosion is still the dominant problem on 706 million acres of rural private land. Nearly a fourth of our 437 million cropland acres is subject to a critical rate of damage. Another fourth is being damaged at a somewhat less critical but still serious rate. In addition, every year more than a million acres are being taken out of agricultural use and put into highways, urban development, airports, and other non- agricultural uses. 20 |