Fertilizers and Fertility. 351 



The following general plan would seem worth working toward: 

 secure the greatest amount of nitrogen through manures, feeds and 

 leguminous crops and, thereby, save the cost of the most expensive con- 

 stituent in fertilizers. Nitrogen costs from fifteen to twenty cents per 

 pound. 



In an experimental way, try the purchase of phosphoric acid alone 

 in the form of dissolved rock. The ordinary stable manure is more 

 deficient in phosphoric acid than in other constituents. The plaster of 

 the dissolved rock, and the decaying humus from the manures, in many 

 cases will furnish sufficient potash from the soil. 



Chemical analysis may or may not afford a guide to the fertilizer 

 needs of the soil. Most often it does not furnish a reliable guide, although 

 it may at the same time give useful hints and suggest what further lines 

 of study may be pursued. This subject is discussed in Bulletin No. 3, 

 to which these notes are intended to form an appendix. Chemical analysis 

 is only one of the means of determining soil fertility questions. Careful 

 tests by means of crops, under conditions of control, usually give safer 

 farm-practice results than mere chemical analysis. 



