NEED OF COMMERCIAL FERTILIZERS 



manures are rich in nitrogen, and when the scheme 

 of farming involves their use on all the land of the 

 farm, no need of purchased nitrogen may arise 

 in the production of staple crops. In the black 

 corn soils the nitrogen content originally was 

 high. 



Lands that naturally are not very fertile rarely 

 have enough available nitrogen. Where timothy 

 is a leading crop, the demand for nitrogen is heavy. 

 A cold spring or summer, checking nature's pro- 

 cesses in the soil, may cause a temporary defi- 

 ciency in available nitrogen in land that usually 

 has a sufficient supply. Associating a rank growth 

 of stalk and leaf with an abundance of nitrogen, the 

 experienced man can form a pretty safe opinion 

 regarding the probable profitableness of an in- 

 vestment in this element. It costs nearly four 

 times as much per pound as either of the two 

 other constituents of a fertilizer, and so far as is 

 feasible it should be obtained through the legumes 

 and stable manure. 



Phosphoric-acid Requirements. Soil analyses 

 show that the content of phosphoric acid in most 

 soils of this country is relatively small. The re- 

 sults of experiments with the various constitu- 

 ents of fertilizers are in accord with this fact. 



[165] 



