286 SOILS AND FERTILIZERS 



care is taken of the manure, and in place of the grains 

 sold mill products are purchased and fed, there is no 

 loss but often a gain of fertility. Between these two 

 extremes, exclusive grain farming and stock farming, 

 many different systems are practiced which remove 

 from the soil various amounts of fertility. 



344. Two Systems of Farming Compared. Losses 

 of fertility from farms are determined by the products 

 sold, the care of the manure, and the fertility in the 

 materials purchased and used on the farm. If an ac- 

 count were kept of the income and outgo of the fertility 

 it would be found that with some systems the soil 

 is gaining, while with others a rapid decline is occur- 

 ring. In studying the income and outgo of fertility, it 

 is necessary to calculate the amounts of the three prin- 

 cipal elements, nitrogen, phosphoric acid, and potash in 

 the crops and other products sold. For making these 

 calculations, tables are given in Sections 185 and 307. 

 In the handling of manure it is impossible to prevent 

 losses, but it is possible to reduce them to very small 

 amounts. Hence in the calculations, a loss of 3 per 

 cent is allowed for mechanical waste and for uneven 

 distribution of the manure ; that is, in addition to the 

 fertility sold from the farm a mechanical loss of 3 per 

 cent is allowed for all crops raised and consumed as 

 food by stock. 



On one farm the crops raised and sold are : flax 40 

 acres, wheat 50 acres, oats 20 acres, barley 50 acres. 



