THE SOIL AND ITS IMPROVEMENT. 113 



These commercial fertilizers are all valuable solely for the 

 plant food they contain, having no beneficial action on the soil, 

 such as is produced by barn-yard manure or green crops. 



Valuation of Fertilizers. It would of course be im- 

 possible to adopt any standard of valuation which could show 

 exactly what any particular fertilizer would be worth to the 

 farmer. That would depend on his soil and crop. A certain 

 fertilizer might, from the nitrogen it contained, be worth forty 

 dollars a ton, and yet on some field or crop that did not need 

 nitrogen it would be worth nothing. But for convenience in 

 comparison experiment stations have adopted certain standards 

 of value for nitrogen, phosphoric acid, and potash. By these 

 standards the intrinsic value of different fertilizers can be deter- 

 mined, and by their means and analysis a farmer can determine 

 whether he is paying more for a fertilizer than it is really 

 worth, and he can compare the value of commercial fertilizers 

 with barn-yard, and he can compare different kinds of barn-yard 

 manure with each other. 



The same article of plant food has a different value, accord- 

 ing to the condition it is in. A pound of nitrogen in nitrate of 

 soda is worth more than a pound of nitrogen in barn-yard 

 manure, for the nitrogen in the former article will be almost all, 

 and immediately available for the use of the crop, while the 

 nitrogen in the latter may have to lie in the soil for many 

 years before it will be converted into available forms. We shall 

 give in this book the valuations adopted by the Ohio State 

 Board of Agriculture. 



Value per pound. 



Ammonia, .......... 18 cts. 



Which is equal to nitrogen, 21.86 " 



Phosphoric acid in compounds which are soluble in water, and 

 which is described in official analysis as "soluble" phos- 

 phoric acid, 12 eta. 



Phosphoric acid in compounds which though insoluble in water 

 are yet available as plant food, and which is described in 

 official analysis as " reverted phosphoric acid," . . 10 eta, 



Phosphoric acid in insoluble compounds which must undergo 

 decomposition in the soil before being available as plant 

 food, and which is described in official analysis as "insolu- 

 uble phosphoric acid," 5 ct. 



Potash, 6 " 



