44 PRINCIPLES OF FARM PRACTICE 



by making its structure more favorable for crop production, 

 and for the purpose of promoting chemical and bacterial 

 action. The most valuable of these substances is lime, al- 

 though land plaster, common salt, and others may be used 

 occasionally. 



How lime benefits the soil. Some of the calcium which 

 occurs in lime is needed by plants as plant food, but lime 

 has other important uses also that make its presence in the 

 soil desirable. Lime is used to bring about granulation in 

 clay soil; to liberate or make available such plant-food 

 materials as potash; to neutralize soil acids; and to aid useful 

 soil bacteria in their work. 



Acid soils. Whether or not a soil is aci<l is of considerable 

 importance, for most farm plants do not grow well upon acid 

 soils. Legumes, such as alfalfa and red clover, are especially 

 sensitive to soil acids. A soil is regarded as an acid soil (i) 

 when acids are actually present in injurious amounts, or 

 (2) when the soil is deficient in lime. In either case an appli- 

 cation of lime is needed to restore favorable conditions for 

 the growth of plants of greatest value in general farming. 



How to know when lime is needed. Even in limestone 

 regions lime is often lacking in the soil, particularly on old 

 farms. It is a safe practice to test the soil of each field in 

 order to determine whether lime is present or not. There 

 are several simple tests that may be applied. The following 

 is suggested: Add several drops of a weak acid, such as 

 dilute hydrochloric acid, to a handful of the soil; if small 

 bubbles of gas appear the presence of lime is indicated; if 

 no bubbles appear and there seems to be no action of the 

 acid on the soil, the absence of lime is indicated. 



How to lime the soil. Experience has shown that finely 

 grouud limestone is the most economical and satisfactory 



