Manures and Commercial Fertilizers 113 



mixture is what it contains that is of value as plant food 

 and not what the fancy-brand name may be. 



Different crops use nitrogen, phosphoric acid, and pot- 

 ash in different amoimts, some selecting nitrogen and 

 phosphoric acid mainly, while others call for a large per- 

 centage of potash in proportion to the other ingredients. 

 Hence, while a certain ready-mixed fertilizer may be well 

 suited to one crop it may not be as well suited to another 

 one. Then, too, the soil on one man's farm may be 

 mainly deficient in nitrogen and phosphoric acid, while 

 another farm near by may be especially deficient in pot- 

 ash. Therefore the same fertilizer would not be the best 

 for both, for it will, if it has a sufficient percentage of 

 potash for the latter, make the first man buy what his soil 

 does not particularly need. From these facts there has 

 arisen the practice of home-mixing of fertiHzers. 



Knowing that what we want is the proper 

 ^^F^^ tT^"^^ percentage of nitrogen, phosphoric acid, and 

 potash for the various soils and crops, one 

 need only buy the nitrogen he needs in the most accessible 

 form, the phosphoric acid in like manner, and the potash 

 also, and he can readily mix these with the aid of a shovel 

 and a sand screen on a barn floor, can do it as well as it 

 can be done in any factory, and can save a great deal of 

 the cost. Nitrogen can usually be had more cheaply in 

 nitrate of soda than in any other form. But in mixing a 

 fertilizer it will not do to use the nitrate of soda alone as a 

 source of nitrate, for it is so readily dissolved that it must 

 be used at once by the plants or is washed away. It is 

 useful in the start, but we must have in addition to the 

 nitrate some organic nitrogen Hke that contained in cotton- 



