Food for or, as it forms no fixed compounds in the soil, there may be a 



^° ^ loss from leaching into the drains when applied previous to 



^^^ the growth of the plant or in too large quantities at the 



wrong time. 



In the fourth place, it should receive careful attention, 



because its right use as a Nitrate — its most available form — 



permits, not only an economical utilization by the plant, but 



a control of its growth; it may be used in such a way as to 



change the natural tendency, and thus improve it for specific 



uses; thus, in addition to the increase in yield which it may 



cause, It enhances the market value of the plant. 



_,, t- • * -J As already pointed out, the mineral ele- 

 Pnospnoric Acid -^ S i i i • • i 



, p , ments — potash and phosphoric acid — are 



j..„ , relatively cheap as compared with Nitrogen. 



^. In the case of potash, the availability of the 



different forms in which it is usually ob- 

 tained is not a matter of great importance, since all forms 

 are soluble in water, distribute freely in the soil and are 

 readily absorbed by plants, while in the case of phosphoric 

 acid the soluble and immediately available forms contained 

 in superphosphates may be obtained quite as cheaply as many 

 of the insoluble forms, as animal bone and tankage, which are 

 not so immediately useful; besides, these mineral elements, 

 however soluble when applied, are fixed by the soil, and are 

 thus not liable to rapid loss by leaching. When the farmer 

 applies the "minerals," or materials containing potash or 

 phosphoric acid in their best forms, his initial expenditure 

 is not so great as for an equal amount of Nitrogen; besides, 

 he can depend upon their presence there during the growing 

 season, and also that the plants can make use of the constitu- 

 ents; if the one season's growth of the plant does not use the 

 entire amount supplied, the residues will remain for future 

 crops, though they may be less readily acquired by them. 

 These conditions are quite different from those obtaining 

 when available nitrogenous materials are used, and are the 

 basis of the suggestions frequently made to furnish the soil 

 with an excess of the minerals, but adjust the Nitrogen to 

 the needs of the plant. 



A very important thing to remember in the application 

 of Nitrogen, however, is that, though it may appear very 

 efficient, it cannot fulfill all the conditions of a complete 

 fertilizer — it is not a complete food in itself; it is only an 



