6 Food ron Pi.axts. 



The largest deposits of rock jjliosphates exist in South 

 Carolina, Florida and Tennessee. These beds of phos- 

 phate 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 sul- 

 phuric 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 super- 

 phosphate, or acid phosphate, contains about 14 per cent, 

 of soluble phosphoric acid. 



The best sources of potash are sul- 

 Potashes. phate 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 2i^ per cent, of phosphoric 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 

 Nitrate. etfective 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 tankage. 

 But none of these furnish Nitrogen in the Nitrate form 

 in which it is taken up by plants. This can only be fur- 

 nished to plants in the form of Nitrate of Soda. Nitro- 



