6 FOOD FOR PLANTS 



The largest deposits of rock phosphates exist in 

 South CaroHna, Florida and Tennessee. These beds 

 of phosphate are supposed to be composed of the 

 petrified bones and excrements of extinct animals. 

 When this substance is ground and mixed with a 

 sufficient quantity of sulphuric acid, the larger part 

 of the phosphoric acid which it contains becomes 

 available as plant food. This fact was one of the 

 greatest agricultural discoveries of the age. 



When the rock phosphate is thus treated with sul- 

 phuric acid, it becomes what is commercially known 

 as superphosphate, or acid phosphate. The same is 

 true if ground bone is treated in the same way. 

 Good superphosphate, or acid phosphate, contains 

 about 14 per cent, of soluble phosphoric acid. 



The best sources of potash are sulphate of potash 

 and unleached wood ashes, which latter contain from 

 3 to 5 per cent, of potash in the form of carbonate. 

 They also contain from 1 to 2j^ per cent, of phos- 

 phoric acid. They are valuable as plant food for the 

 potash as well as for the valuable lime they contain. 



Nitrate is the most important and effective element 

 of plant food, and at the same time, as stated, is the 

 one that is generally deficient in the soil. 



Crops must have meals, that is, food cooked for 

 them in advance. The sun will help do this cooking, 

 as its heat and light promote nitration which is really 

 a process of cooking and also pre-digestion. When 

 the nitrogenous plant food is cooked and prepared 

 for use it is Nitrate, hence Nitrate of Soda is in a 

 class by itself, different from all other plant foods. 



There are a great many sources of Nitrogen, such 

 as dried fish, cotton-seed meal, dried blood, and 



