SOILS AND FERTILIZERS 



105 



1680 Lbs, INDIAN CORN 



cultivation also has a tendency to decrease considerably 

 the humus in the soil. To get maximum crops of corn 

 and to maintain the fertility of the soil, liberal applica- 

 tions of animal manure and of mineral fertilizers should 

 be made. 



Classes of Fertilizers according to Source. A farm 

 that is well organized and well managed has usually 

 in its own products .nearly 

 all of the fertilizers needed 

 to keep itself in a productive 

 condition. By the occa- 

 sional plowing under of cer- 

 tain green crops, called green 

 manuring, much humus is 

 returned to the soil, while 

 the careful conservation and 

 proper use of animal manure 

 from the barnyard renders 

 unnecessary so much of 

 other fertilizers. 



Farmers who do not have 

 animals on the farm and 

 thus provide for a plentiful 

 supply of barnyard manure, and who do not green 

 manure their land, must resort to what are known 

 as commercial fertilizers ; that is, compounds of ni- 

 trogen, phosphorus, and potassium prepared or manu- 

 factured. These fertilizers are expensive, especially 

 those containing nitrogen, but some farmers use them 

 and let the manure go to waste. 



Green Manure. Crops of buckwheat, rye, clover, 

 or cowpeas are sometimes planted to be plowed under 

 with the purpose of adding humus to the soil through 



LJ 



CD-'- 

 '.Ov 1 

 Ct . 



h- 



FIG. 41. Showing Plant Food taken 

 from Soil by Corn. 



