GRAIN FARMING 23 



the surface. Soil washing may also be i)reveiitc(l to some 

 extent by applying straw either on the surface or in the texture 

 of the soil by plowing it under. 



Soil Bacteria. — A most important element of soil fertility 

 is its bacterial hfe. Bacteria in general are small living 

 organisms made up of only a single cell. They are so small 

 ordinarily that they cannot be seen. In order to be able to 

 see them one must have a very strong microscope which 

 makes them appear hundreds and even thousands of times as 

 large as they really are. They live, grow, increase in numbers, 

 and also die. When they die they leave a carcass or dead 

 body in the soil which is very rich in the things needed for 

 plant grow^th. They also eat or dissolve the dead roots, 

 manure, grass, weeds, etc., and thus put them into forms fit 

 for use as foods by growing plants. The bacteria, by their 

 mode of living and b}^ means of the waste products they give 

 off, also, actually help to dissolve soil particles and make 

 available other substances which plants need as food. A soil 

 that is well supplied with these bacteria, therefore, is a better 

 soil than one that is poorly supplied. 



Most productive soils in their natural state are covered 

 with leaves, grass, weeds, etc. This material furnishes the 

 bacteria with food and at the same time protects them from 

 the sun. Sunlight will kill most bacteria, not by its heat but 

 because of other qualities. This is one reason why new soil 

 when it is first broken or plowed up is so rich and will produce 

 such good crops. 



In grain farming, the crop is cut in the middle of the sum- 

 mer and the soil is exposed to direct sunlight during a large 

 part of the season when the light is the most intense. This has 

 a very damaging effect on the soil. Then when the land grows 

 poorer and will not grow crops continually, it is summer 

 fallowed. This again exposes the soil to the direct rays of the 

 sun for a long period, killing all the bacteria on the surface. 

 Land so treated is benefited in some ways but it is materially 

 damaged by the loss of its bacterial life. It has been found in 

 fact, that by growing a cultivated crop, such as corn or po- 

 tatoes, the soil receives the same benefit as by summer fallow- 

 ing and the succeeding crop is just as good. The reason is 



