Soil Fertility 95 



formerly grew good crops of red clover are now not producing 

 this valuable legume and very often an application of lime is 

 all that is required to renew this stand. Often failures in grow- 

 ing alfalfa are due to the soils not being sufficiently limed. 

 Field peas, cowpeas, soybeans, vetches, white clover, alsike 

 clover, and bur clover will grow on soils low or even slightly 

 deficient in lime ; nevertheless they will respond favorably 

 to an application of lime and make better growths. Florida 

 beggarweed and velvet beans seem to prefer an acid soil and 

 lime is not required on soils to be planted to these crops. 



Supplying calcium by lime. Calcium as a plant-food is 

 found in sufficient quantities in most soils. However, analyses 

 have been made of some soils in the Eastern and Southern 

 States that show a deficiency of it. In soils of this kind, the 

 marked response on an application of lime may be due partly 

 to the favorable effect of the added supply of the plant-food. 



44. Forms of lime. Three forms of lime are in use by 

 farmers for soil improvement. They are ground limestone, 

 caustic lime, and hydrated lime. Limestone (CaC0 3 ), or car- 

 bonate of lime, is found as natural deposits in many parts 

 of the country. For soil improvement it is ground to a powder 

 and applied to the land without further treatment. Marl, 

 chalk, and oyster shells contain carbonate of lime and can, if 

 ground, be used as ground limestone. Caustic lime (CaO), 

 also known as burnt lime and as quick-lime, is made by heating 

 limestone until carbon dioxide (CO 2 ) is given off. It is called 

 caustic lime because it decomposes organic substances. Thus 

 it burns humus out of the soil. When moistened it unites 

 with water and forms hydrated lime (Ca(OH) 2 ). Either caus- 

 tic lime or hydrated lime when placed in soil soon reverts 

 to the carbonate form. When one hundred pounds of pure 

 limestone is burned, fifty-six pounds of quick-lime is formed 

 and the fifty-six pounds of quick-lime when treated with water 

 will make seventy-four pounds of hydrated lime. Thus, as 

 far as correcting soil acidity is concerned, one hundred pounds 



