84 MAINE AGRICULTURAL EXPERIME;NT STATION. 191I. 



influence upon availability as is the case with nitrogen and 

 phosphoric acid. All ordinary 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 experi- 

 ments seem to indicate that the quality of tobacco, and certain 

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

 potash, while the same crops show a superior quality of materials 

 free from chlorides have been used as the source of potash. 



Valuation of* Fe;rtilize;rs. 



The agricultural value of any fertilizing constituent is meas- 

 ured 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 cannot 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 last 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 ommercial or 

 market value, it may happen that an element in its most avail- 

 able form, and under ordinary conditions of high agricultural 

 value, costs less in market than the same element in less avail- 

 able forms and of a lower agricultural value. The commercial 

 value has reference 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 

 materials 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- 



