PHOSPHATE PERTILIZERS 



197 



a by-product in the manufactui'e of coke and illuminating gas. 

 In the soil this fertilizer undergoes decomposition and nitrification. 

 It has been found that corn, peas and rice can use nitrogen directly 

 from this salt. This fertilizer has about nine-tenths the efiiciency 

 of nitrate of soda, and it may be used in a similar manner. The use 

 of ammonium sulfate will no doubt become more general than 

 formerly, since the nitrate deposits are destined to exhaustion in 

 a few generations. 



Dried blood is the evaporated, dried and finely ground blood 

 of slaughtered animals. This is one of the best organic nitrogen 

 fertilizers. Under proper soil conditions it proves about ninety 

 per cent as efficient as nitrate of soda. 



Cottonseed meal is a product formed when oil is removed 

 from cotton seed. The extracted residue is ground fine. It is 

 extensively used as a fertilizer in the South. 



This material, as well as all other available nitrogen-containing 

 substances, are much used in the manufacture of mixed fertilizers. 



Legumes to Solve Nitrogen Problem. — The demand of all 

 crops for nitrogen is greater than for the other elements. (See 

 Table of Crop Requirements, Chapter VI), This, together with 

 the fact that the conditions of life in the civilized quarters of the 

 globe are such as to cause a constant loss of nitrogen, has caused 

 the question of the available nitrogen supply of the world to be 

 looked upon as lying at the very foundation of agriculture, and 

 to demand most careful consideration. One of the greatest prob- 

 lems in the maintenance of soil fertility is how to secure and keep 

 a sufficient supply of available nitrogen at the least cost. This is 

 too large a problem to be solved through the use of commercial 

 nitrogen fertilizers alone. It is now generally agreed that legumes 

 must play the larger part in the solution of the nitrogen problem. 

 Moreover, it should be remembered that fertilizers can never 

 become a substitute for the organic matter so essential in all soils. 



Phosphate Fertilizers. — The common phosphate fertilizers are: 



Common names 



Per cent 

 phosphorus (P) 



Per cent 

 phosphoric 

 acid (P2O5) 



Availability of phos- 



phorus-contaimng 



mgreckent 



(a) Rock phosphate 



(6) Basic slag, or Thomas slag 



(c) Ground stefimed bone 



meal* 



(d) Acid phosphate 



11 8 to 13.5 

 4.5 to 8 



10 to 11 

 5 7 to 8 



= 27 to 31 

 = 10 to 18 



- 23 to 25 

 = 13 to 18 



Insoluble. 



Less than bone meal. 



Medium. 

 Eeadily available. 



* Ground steamed bone meal also contains 2 to 3 per cent nitrogen. 



