THE SOIL AND ITS IMPROVEMENT 93 



is to have no fertilizer and is called tlie " check " can, to be used 

 for comparison with the others. No. 2 is to be watered with nitrate 

 of soda solution made by dissolving one teaspoonful in a gallon of 

 water; No. 3 one-half as much as No. 2, and No. 4 one-fourth as 

 much as No. 2. After a few weeks' trial, determine which amounts of 

 nitrate suit this kind of soil best. In each case, when the amount of 

 fertilizer mentioned has been used, do not use any more, but continue 

 to use clear water. 



Soils which have an abundance of organic matter or of other 

 nitrogenous material do not require as much nitrate to produce 

 the best plant growth. The rate of application mentioned in 

 this exercise for can No. 2 is approximately 500 pounds per 

 acre, or about six ounces for a ten-foot row of the garden. 



This test and a number of other fertilizer tests should be 

 •made with samples taken from gardens, so that the gardener 

 may know how strong, and what kind of fertilizer to apply. 



Phosphoric acid is found abundantly in nature in com- 

 bination with lime and other materials. Phosphate rocks are 

 found in deposits in South Carolina, Florida, Tennessee, Utah, 

 Idaho and Wyoming. This rock is used as fertilizer because 

 of the phosphorus which it contains. The rock is sometimes 

 ground very fine and applied to soils directly. In this form 

 it is commercially known as ground rock phosphate or " floats." 

 It yields its phosphorus to plants very gradually and remains 

 in the soil for years. A second and perhaps more common 

 form of using the phosphate rock is to grind it very, fine, and 

 then treat it with sulfuric acid, which is called " acid phos- 

 phate," or "superphosphate." It may contain as much as 

 twenty per cent of phosphoric acid, but more commonly 

 contains fourteen to sixteen per cent. About four to six 

 ounces of high-grade acid phosphate will be enough for a 

 single garden row ten feet long. 



Bones contain phosphate. Fertilizers containing bone are 

 by-products from slaughter-houses. Bones and the various 

 other wastes are thrown into a tank and the grease extracted. 

 That which remains is called bone tankage. It is usually 



