26 FERTILIZERS 



It may be used to best advantage on trees which 

 have made strong, nitrogenous growth at the ex- 

 pense of fruit production, and also on peaty soils, 

 poor in lime. Water will not dissolve slag, there- 

 fore it should be put in as deeply as possible. 



PHOSPHATE GUANOS. 



39. The guanos of bats and sea fowl are also 

 valuable sources of phosphoric acid. These materi- 

 als, however, vary in analysis very much. Each 

 consignment should be analyzed and its price based 

 on its contents. The first shipments from a guano 

 deposit are usually the richest and most valuable, 

 and may deteriorate as the deposit is drawn upon. 



CHEAPEST FORM OF PHOSPHORIC ACID. 



40. The Pennsylvania State Department of Agri- 

 culture, in Bulletin No. 94, gives the results of 12 

 years' experiments with phosphates, both acidu- 

 lated and unacidulated, and seems to show conclus- 

 ively that the best form in which to purchase phos- 

 phoric acid is the untreated bone or rock. This is 

 only on condition that there is plenty of organic 

 matter, or humus-forming material, in the soil. 



Under such conditions (with humus in the soil) finely 

 ground rock (unacidulated) gave better results than 

 acidulated rock or bone. This was from the stand- 

 point of both original cost of material and the 

 results obtained, and was true of all crops tried, 

 except wheat. Unacidulated fertilizers always con- 

 tain more phosphoric acid than the same fertilizers 

 acidulated, as the weight of the acid used displaces 

 some of the material, and if organic matter is used 

 with the former, the conditions thus created in the 

 soil give it additional life which takes the place of 



