14 



blood, tankage and wool waste. The value of organic material in improving the 

 physical nature of soils is a well established fact, but to buy large quantities of 

 nitrogenous organic fertilizer as a source of organic matter to the soil cannot 

 be considered economical. Farmyard manure is a cheap source of organic matter, 

 but where it cannot be produced its place may be taken by growing a catch crop 

 of rye, mustard or clover ready to be plowed under as green manure. 



In brief, we may say regarding the three forms of nitrogen that if during a 

 rotation a quick result is needed within one season a supply of nitrate and 

 ammonia nitrogen will be most effective. On the other hand, if the effect of the 

 manure is required only after considerable time and then a gradual supply is 

 needed, organic nitrogen would be most suitable. 



PHOSPHATIC MANUEES. 



Several materials are used as a source of phosphoric acid. Chief of these 

 are superphosphate, bone meal, ground rock phosphate, and basic slag. The bone 

 meal has been referred to under organic manures and need not be discussed here. 



Ground Eock Phosphate. 



This material differs from those of animal origin mainly in the fact that 

 it is not comibined with organic matter and is more dense and compact in its 

 structure. The phosphate is got in South Carolina, Florida, Tennessee and some 

 of the Eastern Provinces of Canada. It varies in composition, but contains from 

 25 to even 40 per cent, of phosphoric acid (P=Or). The phosphoric acid in this 

 material is in the form of the tricalcic phosphate, and therefore insoluble in 

 water, and is very slowly rendered available. Fine grinding is the means used 

 to increase the solubility. Dependence is placed upon the acids formed by the 

 decaying organic matter to bring this material into solution. 



Basic Slag. 



Basic slag, or Thomas phosphate, is a very finely ground, heavy black powder. 

 It is a by-product in the manufacture of steel from iron and contains from 12 

 to 20 per cent, of phosphoric acid (P2O5). The availability of the phosphoric 

 acid in the crude basic slag varies greatly, even as much as from 20 to nearly 

 100 per cent. Consequently, care must be exercised in the selection of the material 

 that is to be prepared for use as a fertilizer. The better forms on the market 

 contain from about 11 to 13 per cent, of available phosphoric acid. This is in the 

 form of tetra-calcic phosphate, which appears to be more soluble under soil 

 conditions than the tri-calcic phosphate, "The standard for fineness is that 80 

 per cent, of the material should pass through a sieve with 10,000 openings to 

 the square inch. 



Superphosphate or Acid Phosphate. 



Years ago, when phosphoric acid was recognized as an essential plant food 

 constituent, bone meal was the chief source of this material. To increase its 

 availability the bones were ground to a very fine powder, but even tliis did not 



