196 FARM MANAGEMENT 



but even when these are used, the farmer should take 

 advantage of the natural means so far as possible. 



MAINTAINING THE MINERAL MATTER OF THE SOIL 



126. Sources of mineral matter. The only way to 

 keep up the mineral matter of the soil is to add the par- 

 ticular elements that are present in too small quantities. 

 The mineral that is most likely to be present in too small 

 quantities is lime. Fortunately, the supply of limestone 

 in the world seems to be inexhaustible, so that the ques- 

 tion of using it is simply one of the cost of lime and bene- 

 fits from its use. Some soils have all the lime that they 

 need, but much over half the soils east of the Mississippi 

 River would be benefited by lime. Lime is also the most 

 frequent need in England. 1 



The form of lime to use seems to be primarily a ques- 

 tion of the cost of calcium, and the expense of applica- 

 tion. Fifty-six pounds of pure burned limestone, or 

 quicklime, is equal to 74 pounds of hydrated lime, or 100 

 pounds of ground limestone, or air-slaked lime. Wood 

 ashes are about one-third lime. 



Potassium is fairly abundant in most soils in America, 

 but is needed in many places, particularly on sandy and 

 swamp soils. 



Phosphorus is practically always deficient on soils that 

 need lime, and occasionally on soils that are well supplied 

 with lime. 



If any one of these minerals is deficient, it may be added 

 by using fertilizers or farm manure. 



No method of farm practice will add to the supply of 

 any of the mineral substances, but the rapidity of loss is 



1 The Soil, A. D. Hall, p. 243. 



