66 CROP GROWING AND CROP FEEDING 



covered in Central Tennessee. This has a high percentage of phosphate of 

 lime, and will become the most important point from which to get phosphoric 

 acid in the Central Western States. Another deposit has been discovered in 

 the Juniata Valley of Pennsylvania, but whether it vvill assume any com- 

 mercial importance is not yet known. Hard phosphate rock, which will yield 

 on dissolving with sulphuric acid a good, drillable acid phosphate will always 

 be of more agricultural value than those not adapted to this purpose. 



While phosphoric acid may exist in the form of iron phosphate and of 

 aluminum phosphate, the only form in which it is available in the manu- 

 facture of commercial fertilizers is the phosphate of lime. This is the form 

 in which it is found in phosphatic rock and in animal bones, and hence manu- 

 facturers, whose product does not contain a solitary animal bone, are very 

 fond of printing on their bags the statement that the percentage of phosphoric 

 acid in it is "equal to bone phosphate;" thus leading the farmer to imagine 

 that there are bones used in it, as they think that farmers value phosphoric 

 acid from bones more highly than the same thing from some other source. 

 I cannot too often repeat that it is the percentage of availability that the 

 farmer is concerned with, and not whether it came from bones or 

 rock. All untreated phosphates are insoluble in water, and untreated 

 bone will become available more readily than untreated rock phos- 

 phate, because it decays more readily, provided both are in an equally finely 

 pulverized state. Many farmers have declared that they get as good results 

 from the pulverized phosphates as from the acid phosphate, and in certain 

 soils this may be the case, for the character of the soil has much to do with 

 the rate in which the phosphoric acid in an untreated phosphate becomes 

 available. In a soil abounding in humus, or vegetable decay, the phosphates 

 will become soluble more readily than in a heavy, clay soil deficient in organic 

 decay. In the porous soil, filled with humus, the oxidizing influences of the 

 air have free access, and decay proceeds more rapidly, while the acidity of 

 such soils also favors the change. For general purposes it is far better, how- 

 ever, to use the acid phosphate than the lower priced pulverized rock or the 

 iron phosphate. Professor Voorhees well says that, "In any case, animal 

 bone, or finely ground mineral phosphates, cannot be depended upon to fully 

 meet the needs of quick growing crops for phosphoric acid, but may answer 

 an excellent purpose where the object is to gradually improve the^soil in its 

 content of this constituent, as well as to supply such crops as are continuous, 

 or that grow through long periods, as, for example, meadows, pastures, and 

 orchard and vineyard crops." That is to say, that where you can afford to 

 wait and where you want long-continued, slow availability, it may pay to use 

 the more slowly available forms of phosphoric acid, but where you want the 



