326 AGRICULTURE 



acid. (2) The presence of such weeds as sheep-sorrel, 

 horsetail rush, corn spurry, and wood horsetail indicate 

 acid. (3) Blue litmus paper turns red when placed in con- 

 tact with a soil containing acid. (4) Acidic test. (See 

 Wisconsin Bulletin No. 249 for new method.) 



Liming acid soils. Lime is a certain remedy for acid 

 soils. In some regions, especially where limestone abounds, 

 the natural supply of lime in the soil is sufficient to overcome 

 the surplus acid. In other regions, lime needs to be applied 

 in commercial form. This is the only cure for acid soil 

 within reach of the farmer. 



Nearly all prairie soil is in some degree acid, especially 

 on slopes where leaching of the soil has carried away the 

 original deposits of lime, and wherever large supplies of 

 humus have formed from the decay of organic matter. 

 Thousands of acres of acid land would well repay the cost 

 of liming by increased yields. Many farmers now look on 

 liming as a regular and necessary requirement. Of course 

 lime should not be applied unless needed, but the tests are 

 so simple that this is easily determined. 



Forms of lime used. Lime is available for applica- 

 tion to the soil in several forms : ( 1 ) Quicklime, or lime 

 ready for use in making plaster, when finely ground may be 

 applied at the rate of about one ton to the acre. (2) Air- 

 slacked lime, or ordinary lime that has been exposed to the 

 air, is an excellent form, and may be applied at the rate 

 of two or more tons to the acre. (3) Ground or finely 

 crushed limestone direct from the quarries is widely used 

 in regions where it is easily obtainable. From one to two 

 tons to the acre will usually correct the acidity. 



The form of lime to be used will depend chiefly on which 

 is most easily available and cheapest. The amount required 

 is determined by the degree of acidity in the soil. 



