SOURCES AND COMPOSITION OF FERTILIZERS 303 



inch, compared with nitrate of soda as 100, it was 11.3; 1/150 to 

 1/50 inch, 8.5; and 1/25 to 1/50, 5.6. 



Any agency which accelerates the transformation of organic 

 bodies into assimilable compounds would increase the availability 

 of the nitrogen. The temperature, nature of soil, and activity of 

 the organisms in the soil would thus be of effect. 



Agricultural Value. The availability of a nitrogenous fer- 

 tilizer is measured by the amount of nitrogen which plants can 

 secure from it under the most favorable conditions. Availability 

 does not necessarily represent agricultural value, or crop produc- 

 ing power in the open field, since other factors enter in the ques- 

 tion, some of which are as follows : 



1 i ) Kind of Season. In a very wet season, nitrate of soda is 

 less useful than other forms because it is liable to be washed below 

 the reach of the roots and lost altogether unless applied just when 

 needed, or on a heavy soil. 



(2) Kind of Crop. Some crops grow and develop quickly, 

 while others grow for a comparatively long period. Quick-acting 

 fertilizers like nitrate of soda or ammonium sulphate, would be 

 more effective on the former than organic fertilizers, which must 

 undergo change before their nitrogen is available. The slower- 

 acting organic materials would be better for plants with a long 

 growing period, unless a number of applications of the quick- 

 acting fertilizers are made. 



(3) Season of the Year. The change from organic nitrogen 

 to ammonia or nitrate takes place more readily as the temperature 

 approaches 98 F. Hence the organic materials would be re- 

 latively less effective for winter crops than for summer ones. A 

 material which gives excellent results when applied to a crop dur- 

 a warm and moist season, might be very unsatisfactory when the 

 season is short, cold, and dry. 



Phosphatic Fertilizers. Phosphatic fertilizers are of two kinds, 

 crude phosphates, and treated phosphates. 



Phosphates. The more important crude phosphates are bone, 

 bone tankage, bone black, rock phosphate, apatite, and Thomas 



