PROBLEM 4. Why We Must Practice Conservation 



keep the soil from being washed away 

 and experiment with methods of restor- 

 ing soil fertility. Let us examine some of 

 these methods more closely. 



Contour planting. Most farm land has 

 a slight slope. Water can be prevented 

 from flowing off and carrying away top- 

 soil from slopes by plowing and planting 

 crosswise on the hill instead of up and 

 down it. The furrows catch and hold the 

 water. This is known as contour plowing 

 and planting. Often, too, small ridges are 

 built around the hill to prevent the rapid 

 run-off of water, or the slope is built into 

 a series of terraces. 



Binding the soil. Contour planting and 

 the building of ridges also help to pre- 

 vent a very destructive process known as 

 sheeting. In sheeting, the very top layer 

 of soil slowly but steadily moves down- 

 hill because it is so soaked with water 

 that it is really floating. To prevent this 

 type of soil loss, farmers can plant cover 

 crops, whose chief value is to bind the 

 soil. Sometimes the cover crop may serve 

 a double purpose. When leguminous 

 plants such as alfalfa and clover are 

 planted as cover crops, they add nitro- 

 gen compounds to the soil. 



Restoring fertility to the soil. When a 

 farmer practices crop rotation he plants 

 alfalfa, clover, beans, or some other legu- 

 minous plant every few years to restore 

 nitrates to the soil. In order to make sure 

 that root nodules develop, farmers often 

 sow small amounts of the necessary bac- 

 teria with the seeds. The bacteria are 

 raised by state agricultural stations, by 

 the United States Department of Agri- 

 culture, and by commercial firms from 

 whom they may be obtained. Farmers 

 also use commercial fertilizers made in 



405 



factories. Such fertilizers contain nitro- 

 gen compounds, phosphates, potassium 

 compounds, and other minerals. They 

 use the decaying solid wastes of farm 

 animals, known as manure; decaying fish, 

 w^hich are exceptionally rich in minerals; 

 and the solid wastes of birds, known as 

 giiano (gwa'no). Vast deposits of guano 

 are found on the dry coasts of Chile and 

 southern Peru. 



The vanishing of wildlife. With the 

 destruction of forests and the settling of 

 the plains, great numbers of wild animals 

 and plants were destroyed. Elk once 

 roamed our eastern woods. Bison were 

 seen by the first white men who landed 

 in what is now Maryland. They lived in 

 the region where the White House stands 

 today. The California grizzly bear is 

 gone. Birds, too, have been crowded out 

 and become extinct. In 1 844 the last great 

 auk died. The year 19 14 saw the end of 

 the passenger pigeons, which at one time 

 were widely used as food and could be 

 bought in the market for a penny a bird. 

 As recently as 1932 heath hens became 

 extinct. The wild turkey which once 

 lived in most of our states is no longer 

 common. 



The tall blue stem grass which over 

 thousands of years built the rich prairie 

 soils of Iowa and neighboring states has 

 been destroyed except for a few scat- 

 tered patches. Much of the giant red- 

 wood forest of the western coast is gone. 

 And many species of wild flowers are 

 being rapidly destroyed. You may have 

 seen warnings in your local post ofiice to 

 protect certain plants which are in dan- 

 ger of becoming extinct. 



What is true of the United States is 

 true of other countries, too. The Soviet 



