110 CONSERVATION AND IMPROVEMENT OF SOIL 



application of lime is the first step in the building up of a worn- 

 out soil. The owner must remember that other methods of 

 improvement must accompany this treatment. 



The need of lime on a field is often indicated when clover will 

 not grow. Sourness in the soil may be detected by the presence 

 of certain weeds, such as sheep-sorrel. It may also be detected 

 by the use of litmus paper, as described in one of the exercises. 

 If the need of lime is doubted by the owner, a small strip instead 

 of the whole field may be treated. This trial may be made upon 

 a field used for clover or almost any other field crop. If marked 

 improvement is shown the owner can easily draw his conclusions. 



Forms of Lime. There are several forms of lime in common 

 use. Some understanding of each of these should be had before 

 lime is applied. Ground limestone is perhaps the most common 

 form used by farmers, particularly in regions where the distance 

 for shipment is not very great. Limestone grinders are in use near 

 stone quarries in all parts of the country. From such grinders the 

 products vary in fineness from a fine powder to a coarse granular 

 state. Commercially the fineness is indicated by the sieves 

 through which the ground stone will pass. That which passes 

 through a sieve of fifty or sixty meshes to the inch will contain 

 some material which is as coarse as this and much more that is a 

 great deal finer. The coarse products used for agricultural pur- 

 poses should be fine enough to go through an eight-mesh sieve. 

 Ground lime as coarse as this can be produced without artificial 

 drying of the stone, but the finest grades must be artificially 

 dried, thus greatly multiplying the cost of production. 



Ground limestone is chiefly composed of carbonate of lime or 

 calcium carbonate (CaCOs). 



Burned lime is extensively used for agricultural purposes. It 

 is prepared in lime-kilns by burning under such conditions as to 

 produce great heat without much moisture or air. The carbonate 

 of lime is broken up by the heat into two compounds; calcium 

 oxide and carbon dioxide, thus CaCO3 = CaO-f-CO 2 . 



The carbon dioxide is driven off into the air and the calcium 

 oxide exists in a form which is sometimes called stone lime, or 

 caustic lime or quick lime. It is this form of lime which is used 

 hi making mortar Tor masonry or plaster. Because of the driving 

 off of the carbon dioxide the weight is reduced nearly one-half. 

 This must be taken into consideration when deciding upon the 

 qualities of lime to be applied to the soils. 



