BUYING PLANT FOOD FOR THE SOIL 235 



if immediate results are desired. If a soil contains plenty 

 of humus, however, it often may be more economical to 

 apply the cheaper, untreated rock. This is especially true 

 if it be applied with decaying organic matter as manure 

 or sod. High-grade acid phosphate is preferable to the 

 low-grade since there is more soluble phosphoric acid in 

 the former and less in the latter. 



In making acid phosphate, ground rock and sulphuric 

 acid are mixed in about equal weights, and as a result 

 the acid phosphate produced has only about one-half as 

 much phosphoric acid per ton as the rock from which it 

 was made. Consequently, we find that acid phosphate 

 contains from ten to nineteen per cent, of phosphoric acid. 



Bone fertilizers. Bone was early used as a fertilizer, 

 and is still popular to-day. The many names for bone 

 raw bone, ground bone, fine ground bone, bone dust, bone 

 meal, and dissolved bone indicate the mechanical treat- 

 ment and physical condition of the fertilizer. 



Ground bone contains from two to four per cent, of 

 nitrogen and twenty to thirty per cent, of phosphoric 

 acid ; steamed bone from one to two per cent, of nitrogen 

 and from twenty-five to thirty per cent, of phosphoric 

 acid ; and dissolved bone from two to three per cent, of 

 nitrogen and from twelve to fourteen per cent, of avail- 

 able phosphoric acid. Bone meal is not a quick-acting 

 fertilizer, hence, this material is not desirable when a 

 quickly acting material is wanted; but for lawns, perma- 

 nent grass lands, and long-growing crops, bone meal is 

 very desirable for both nitrogen and phosphoric acid. 



Treated rock and treated bone are the chief sources 

 of phosphorus for plant food. There are large quantities 

 of each of these materials, and so the cost of phosphorus is 

 moderate in price, and it ought to be used whenever the 

 demands of the soil require it. 



