330 SOILS 



far-reaching practical application. The bacteria 

 in these nodules, which can be seen in various 

 sizes on the roots of most legumes, are so small 

 that it would take 10,000 of them placed side by 

 side to measure an inch. Yet these tiny germs 

 save the farmers of this country millions of dollars 

 that would otherwise have to be spent for fertilisers 

 containing nitrogen. 



If the soil does not need nitrogen, but does need 

 humus, a non-leguminous crop like rye or rape may 

 be grown. The leguminous plants, however, are 

 the great soil "renovators." The clovers in the 

 North and the cowpea in the South have built up 

 thousands of acres of soil and vastly increased their 

 producing power. Most of these plants, especially 

 clovers and alfalfa, benefit the soil in still an- 

 other way; they deepen it through their deep- 

 rooting habit. Clover roots bore down into the 

 soil several feet, bringing up and using plant food 

 that is beyond the reach of the roots of most field 

 crops. This is handed over to the surface soil 

 when the plants are plowed under. But some 

 soils will not grow clover. The kind of crop that 

 should be grown for green-manuring, and how to 

 grow it, depend upon the special conditions of each 

 farm. 



WHEN A GREEN-MANURING CROP MAY BE GROWN 



If the soil is badly "run down," and the land 

 can be used for a green-manuring crop without 

 sacrificing too much, the crop may occupy the 

 ground the entire season or even for several sea- 

 sons, as when red clover is sown in the spring, cut 

 the following year and the second crop of that sea- 

 son plowed under. As a rule, however, it is more 



