New York Agricultural Experiment Station. 55 



Acid phosphate is made by treating natural rock phosphate with 

 about an equal weight of sulphuric acid, thus making the phosphate 

 more soluble (available). Bonemeal is sometimes treated with 

 sulphuric acid in the same way to make acid phosphate; but the 

 product of this treatment is more commonly called dissolved bone 

 or acidulated bone. Acid phosphate made in cither of these ways 

 contains phosphorus in the most readily available form of any of the 

 above-named phosphorus fertilizers. Bonemeal, either raw or 

 steamed (the latter being preferable) is now about the highest- 

 priced form of the above phosphates; otherwise, it has been found 

 a very desirable form of phosphorus. The high prices for bonemeal 

 are due to charging full prices for the nitrogen which it contains. 

 But in buying phosphates one wishes to pay only for phosphorus. 



Basic slag is a waste product from the manufacture of steel from 

 iron ore which contains some phosphorus. In addition to phos- 

 phorus it contains a small amount of lime capable of neutralizing 

 acidity (equal to perhaps 20 per ct. of lime carbonate). The Ohio 

 station has compared equivalent amounts of phosphorus in acid phos- 

 phate, basic slag and bonemeal and found almost identically the same 

 results from the three. The comparisons have been made on two 

 widely different soil types and for a period of 18 years on each. 

 At each place all three forms were compared on each of five differ- 

 ent fields each year in a rotation of corn, oats, wheat, clover and 

 timothy. 



Phosphorus in the form of finely ground natural rock phosphate 

 can be obtained directly from the southern mines at one-third to 

 one-fourth the cost of any of the other three forms. But the phos- 

 phorus in the natural rock is not so readily available as in the other 

 forms, and applied in the way fertilizers are commonly used, a few 

 hundred pounds per acre at the time of seeding, satisfactory results 

 are seldom obtained. However, when applied in connection with 

 liberal amounts of decaying organic matter, such as farm manure, 

 green manure or heavy sods, much more satisfactory results are 

 secured. This is logically explained by the action of the decaying 

 organic matter helping to make the phosphate available, just as 

 it is one of the most important factors in making other mineral plant 

 food in the soil available. It is no objection to the use of rock phos- 

 phate that liberal amounts of organic matter must be used with it, 

 for such is entirely necessary to the most profitable management 

 of soils under any condition; and, as already shown, is about the 

 only profitable way of supplying nitrogen and potassium. 



At the Ohio Experiment Station natural rock phosphate has been 

 compared with acid phosphate as reenforcement for manure. The 

 comparison has been made on three different fields for 15 years in 

 a rotation of corn, wheat and hay. The manure is applied at the 

 rate of 8 tons per acre once in three years, to the corn crop, and 

 40 pounds of acid phosphate or 40 pounds of natural rock phosphate 



