84 PRODUCTIVE FARMING 



crops are used. There are several sources of the nitrogen 

 purchased for fertilizers. Nitrogen is derived from animal 

 or vegetable matter as in meat scraps, dried blood, and 

 cottonseed meal. It is also abundant in sulphate of ammonia 

 and nitrate of soda purchased by fertilizer manufacturers. . 



In the nitrate form it is more quickly useful to the crops, 

 and should be applied to the soil after the plants have started 

 growth. Some of the other forms in which nitrogen is used 

 are very slow in changing to forms available to plants; some 

 of these are hair, leather scraps, garbage tankage, and others. 

 It is very important for the farmer to know the source of 

 the nitrogen in the fertilizer he is buying. For this reason 

 it is becoming a common practice in some sections for farm- 

 ers to buy the fertilizer materials separately and mix them 

 on the farm. 



Phosphoric acid is contained in substances in combina- 

 tion with lime and other materials. Such combinations 

 are called phosphates. Ground bone is one of the chief 

 sources of phosphoric acid in fertilizers. If this is ground 

 very fine it will rot gradually and liberate food useful to 

 growing crops. Animal bone contains on an average four 

 per cent of nitrogen and twenty per cent of phosphoric 

 acid. 



Bone tankage is a by-product from slaughter-houses, 

 made up of various wastes that have been thrown in a tank 

 and the grease extracted. Its value varies considerably 

 according to the amount of meat or of bone in it. 



Phosphate rock has been obtained some time from a 

 number of deposits in South Carolina, Florida, and Tennes- 

 see. Recent discoveries of it have been made in Utah, 

 Idaho, and Wyoming. 



The rock is used in two ways: (1) It is ground very fine 

 and applied to soils, yielding its phosphoric acid to plants 

 very gradually. This form is sometimes called floats. (2) 

 The ground phosphate rock is treated with sulfuric acid 



