42 ELEMENTARY AGRICULTURE 



Barnyard manure is called a perfect fertilizer because 

 it contains all the elements that become exhausted from 

 the soil, namely : nitrogen, phosphoric acid and potash. 

 It is usually easy to get, and for these reasons is 

 generally recommended. Clover, plowed under, will re- 

 store nitrogen to the soil because it has power to take 

 nitrogen from the air, a power which few other plants 

 have. Wood ashes are rich in potash and should never 

 be wasted, but sown on the soil. Commercial fer- 

 tilizers, containing what the soil especially needs, may 

 be bought and applied. When they are wisely applied 

 the profit from their use may be large. The subject of 

 fertilizers and fertilization is a large and very important 

 one to the farmer. It needs much thought and care- 

 ful study, and is only touched upon here in the briefest 

 possible manner. The problems which follow will help 

 to emphasize the points made in this chapter. 



Free Bulletins, U. S. Dept. of Agriculture. 

 Extracts. 



No. 169. Soil Investigations in the United States. 



Table V. 



Showing average amounts of nitrogen, phosphoric acid and 

 potash in fertilizers: 



POUNDS PER TON. 



Phosphoric 



Substance. Nitrogen. Acid. Potash. 



Clover hay 40 Ibs. 10 Ibs. 40 Ibs. 



Straw 10 Ibs. 4 Ibs. 20 Ibs. 



Barnyard manure 10 Ibs. 6 Ibs. 9 Ibs. 



Wood ashes 60 Ibs. 160 Ibs. 



Burned bones 500 Ibs. 



Ground bones 400 Ibs. 



