FERTILIZER INSPECTION. 69 



influence upon availability as is the case with nitrogen and phos- 

 phoric acid. All forms are freely soluble in water, and are 

 believed to be nearly if not quite equally available as food. The 

 form of the potash has an important influence upon the quality 

 of certain crops. For example, the results of experiments seem 

 to indicate that the quality of tobacco, potatoes, and certain other 

 crops is unfavorably influenced by the use of muriate of potash, 

 while the same crops show a superior quality if materials free 

 from chlorides have been used as the source of potash. 



Valuation of Fertilizers. 



The agricultural value of any of the fertilizing constituents is 

 measured by the value of the increase of the crop produced by its 

 use, and is, of course, a variable factor, depending upon the 

 availability of the constituent, and the value of the crop pro- 

 duced. The form of the materials used must be carefully con- 

 sidered in the use of manures. Slow-acting materials can not 

 be expected to give profitable returns upon quick growing crops, 

 nor expensive materials profitable returns when used for crops 

 of relatively low value. 



The agricultural value is distinct from what is termed "com- 

 mercial value," or cost in market. This value is determined by 

 market .and trade conditions, as cost of production of the crude 

 material, methods of manipulation required, etc. Since there is 

 no strict relation between agricultural and commercial or market 

 value, it may happen that an element in its most available form, 

 and under ordinary conditions of high agricultural value, costs 

 less in market than the same, element in less available forms and 

 of a lower agricultural value. The commercial value has refer- 

 ence to the material as an article of commerce, hence commercial 

 ratings of various fertilizers have reference to their relative cost 

 and are used largely as a means by which the different materials 

 may be compared. 



The commercial valuation of a fertilizer consists in calculating 

 the retail trade-value or cash-cost at freight centers (in raw 

 material of good quality) of an amount of nitrogen, phosphoric 

 acid and potash equal to that contained in one ton of the fer- 

 tilizer. Plaster, lime, stable manure and nearly all of the less 

 expensive fertilizers have variable prices, which bear no close 

 relation to their chemical composition, but guanos, superphos- 



