128 ELEMENTS OF AGRICULTURE 



again formed. When quicklime air-slakes it also takes up 

 carbon dioxid from the air. Similar changes take place 

 when it is used on the soil. 



Quicklime, calcium oxid (CaO) is the most common 

 form of lime used for agricultural purposes. Usually a 

 poorer grade is used than for plastering. When this is 

 applied to soil, the same changes take place as in the 

 case of plastering. The lump lime is sometimes finely 

 ground so that it can be applied by machinery. Limestone 

 rock is sometimes finely ground and is applied to the soil. 

 Some firms slake the lime with water and sell the hydrated 

 lime. This is also a powder. 



Fifty-six pounds of quicklime (CaO) are equal to 74 

 pounds of hydrated lime, or to 100 pounds of ground 

 limestone or air-slaked lime. 



The quicklime, or hydrated lime, should not be applied 

 within a week of the time of planting crops, because it 

 is sometimes so caustic as to injure young plants. 



Ashes contain about one-third lime. 



Gypsum or land plaster (CaSO 4 ) also contains lime, but 

 it is not so good as other forms because it contains sulfuric 

 acid. The use of it is rapidly decreasing. 



135. Application of Lime. From 500 pounds to one 

 ton (6 to 30 bushels) per acre is usually enough to apply 

 at one time. The application may need to be repeated in 

 a few years. Formerly much larger applications were 

 made. There are many conflicting reports as to the benefit 

 of lime. Many regions have taken it up, dropped it, and 

 later come to use it once more. The explanation is that 

 with the amounts applied there was enough to last a con- 

 siderable time. 



