The Composition and Use of Fertilizers. 2G3 



may be made gradually available by keeping the soil well supplied 

 with humus, together with occasional liming. 



(5) Availability of Phosphates Influenced by Kind of Crop.- — 

 Different plants have been found to show varying degrees of power 

 to appropriate the same kind of plant food. For example, fine- 

 ground insoluble phosphate rock may be utilized to a greater or 

 less extent by wheat, barley, corn, peas and turnips, while beans 

 and potatoes do not seem benefited. Turnips especially appear 

 to thrive just as satisfactorily on the fine undissolved as on the 

 dissolved rock. When a crop can advantageously use a cheaper 

 form of plant food, it is economy to use that form. 



(c) Availability of Different Forms of Potash. 



There is little difference between the different compounds of 

 potash in respect to the readiness with which plants use them as 

 food. Muriate of potash dissolves a little more readily and is 

 distributed through the soil somewhat more quickly than sulphate 

 of potash. 



Preferences Shown by Plants for Different Forms of 

 Food. — It is a fact of great interest and importance, that one form 

 of a fertilizing constituent is preferred by some plants to the 

 same constituent in another form. This preference is indicated 

 by greater yield or better quality of product or by both. The 

 most striking instance is the effect of potash salts upon tobacco 

 crops. The quality of tobacco is injured by potash in the form 

 of muriate, and hence only sulphate should be used for fertilizing 

 purposes. The quality of sugar beets and of potatoes often ap- 

 pears to be better when sulphate of potash is used. 



Much investigation in this interesting field remains yet to be 

 made. The facts now known are meager, but so far as knoAvn 

 they should be utilized. Whenever a plant shows any marked 

 preference for any special form of food, we should supply that 

 particular form if practicable. 



Economy in Purchasing Different Forms of Plant Food. 

 — ■ Other things being equal, we can effect considerable saving in 

 purchasing fertilizing materials by a careful selection based upon 

 a study of market values. 



The most expensive form in which nitrogen is usually pur- 

 chased is that of sulphate of ammonia. When high-grade sul- 

 phate of ammonia sells for $60 a ton, each pound of nitrogen in 

 it costs about 15 cents. When hicdi-grade nitrate of soda sella 



