Fo pf f ? r °f "available" phosphoric acid or of potash, is an added 



reason for greater care in its purchase and use. 



4° Nitrogen as Nitrate of Soda is the only commer- 



cial form of active Nitrogen available for immediate 

 use by most plants; Nitrogen, as ammonia, is less 

 active and less available than the Nitrate. 



Organic forms of Nitrogen have to decay first, 

 changing to ammonia and then to Nitrate, and are 

 therefore less active and less quickly available; besides, 

 they vary in their rate of availability according to 

 the source of supply and their character. Materials 

 which are likely to decay quickly, as dried blood, dried 

 meat, dried fish and cottonseed meal, show a fair rate 

 of availability, while forms like ground leather and 

 ground peat show a very low rate of availability. A 

 pound of organic Nitrogen varies much in availability, 

 therefore, according to its source, whether derived from 

 dried blood or peat, or from intermediate products, 

 and if much free sulphuric acid is present, its avail- 

 ability is retarded. 



Since Nitrogenous materials are variable in their 

 rate of availability — that is, the rate at which the Ni- 

 trogen in them may be absorbed by the plant — the 

 farmer should know the degree of dependence that can 

 be placed on the different materials — he wants his 

 Nitrogen active and available. Hence, the chemical 

 and physical characteristics of the various forms of 

 Nitrogen have been made the subject of very consider- 

 able study and investigation, in order that approximate 

 values in respect to availability may be assigned to 

 each form. Sufficient work has been done thus far 

 to establish a trustworthy relationship between the 

 Nitrate, ammonia and organic Nitrogen, in the form 

 of dried blood. 



The very extensive investigations conducted at 

 Darmstadt, Germany, show that for the crops tested 

 —namely, barley, oats, rye, wheat, mangels, sugar- 

 beets and potatoes — there was returned in the har- 

 vest 62 parts of Nitrate Nitrogen for every hundred 

 parts applied; 44 parts of ammonia Nitrogen for 

 every hundred parts applied, and 40 parts of organic 

 Nitrogen for every hundred parts applied as dried 



