244 CROP PRODUCTION 



with living germs of many kinds which are continually 

 reacting upon the soil particles and getting plant food 

 into condition for use by crops. The lives of these lowly 

 organisms and the effects which they produce upon the 

 soil are so complicated that they are not thoroughly 

 understood even by the wisest men. We know enough, 

 however, to recognize the fact that this germ life in the 

 soil plays a very important part in the fertility of our 

 fields and that it is highly desirable to furnish condi- 

 tions which are favorable for the development of various 

 kinds of bacteria. Among these conditions we should 

 include an abundant supply of air to be secured throu-gh 

 thorough drainage and frequent tillage and a proper 

 amount of humus well incorporated between the soil 

 particles. Where too much humus is present, however, 

 the soil becomes sour — a condition which is unfavor- 

 able, to the development of bacteria. In such cases 

 the addition of lime tends to sweeten the soil and make 

 it more favorable for germ life. 



These tiny bacteria hve not only in the soil itself, but 

 a very important kind lives in little nodules upon the 

 roots of certain plants. Nearly all of these plants be- 

 long to the great family of legumes, which includes the 

 clovers, beans, peas, vetches, and alfalfa. 



