Commerc'ial Fertilizers. 153 



Experiments indicate that if nitrate of soda is rated at 100 

 per cent, the availability of the other materials will be as follows : 



Per cent 



Nitrate of soda 100 



Blood and cotton-seed meal 70 



Fish (>5 



Bone and tankage 60 



Leather, hair, wool waste, etc 2 30 



This suggests that for those crops which begin their growth 

 early in the spring, the best results will follow the use of Chili 

 salt-petre, as the soil is likely to be poor in nitrates and the 

 process of nitrification slow at that time. Other crops, as corn, 

 for example, which make their growth after the season is well 

 advanced, can use the slower acting fertilizers ; as can those crops 

 which occupy the ground permanently. 



In ordinary farming it is seldom profitable to purchase nitro- 

 genous fertilizers, for the nitrogen of the soil can be maintained 

 by means of farm manures and the proper use of leguminous 

 crops in the rotation. In intensive farming, as market garden- 

 ing, it will be found necessary to make liberal use of nitrogenous 

 fertilizers. 



Phosphatic fertilizers. Materials from which phosphoric acid 

 is derived are called phosphates. Commercial sources of the 

 phosphoric acid of fertilizers are: (1) phosphate rock; (2) bones 

 nd bone preparations; (3) basic slag; (4) guano. 



Phosphoric acid is found in these materials in combination 

 with lime, iron and alumina. In combination with lime it forms 

 three different compounds; (1) insoluble phosphate of lime; (2) 

 soluble phosphate of lime; (3) reverted phosphate of lime. 



Insoluble phosphate of lime is known as "tri-calcium phos- 

 phate," or "bone phosphate of lime" and is composed of three 

 parts of lime in combination with one part, of phosphoric acid. 

 It is insoluble in water and not readily available to plants. The 

 principal materials found on the market containing this form 

 of phosphate are : South Carolina rock, Florida rock, Tennessee 



