LIMESTONE 173 



action and evaporated. More or less acidity is thus brought up 

 from the acid subsoil, especially in time of drouth, and there should 

 be sufficient limestone in the surface to destroy this acidity as it 

 rises. Quantitative determinations have shown that to correct 

 the total acidity contained in much of the upland soil of southern 

 Illinois to a depth of 40 inches would require more than 10 tons 

 of limestone per acre. 



It is not necessary to apply such amounts, because the limestone 

 does not descend very much below the plowed soil, and the rise of 

 acidity from below is only occasional and not rapid. 



It may be said, however, that 10 tons of ground limestone per 

 acre would not only do no harm, but would probably produce 

 somewhat larger crops than any lighter application. As much as 

 10 tons per acre has been applied on an experiment field in southern 

 Illinois, and the crop yields on that field have been larger during 

 the last three years than on any other experiment field in that 

 area. Two to four tons per acre, however, have usually produced 

 much benefit. 



The author has used 2 to 3 tons per acre of magnesium lime- 

 stone on his own southern Illinois farm (gray silt loam on tight clay), 

 and as much as 10 tons per acre of the same material has been 

 used on another farm with evident benefit. He advises an appli- 

 cation of at least 2 tons of ground limestone per acre, where the 

 addition of limestone is necessary, believing that less than this will 

 not give satisfactory results in practice. Heavier applications will 

 give greater profits per acre, but probably less profit per ton of 

 limestone used. 



These two factors, it may be noted, are commonly opposed to 

 each other in many farm operations. Thus, farm manure gives the 

 greatest profit per acre in heavy applications, but the greatest 

 profit per ton in light applications. With little manure and much 

 land we apply the manure lightly, but, with a small area of land 

 and large supplies of manure, we apply it heavily. So, with ground 

 limestone: If one must cultivate much land and can use but little 

 limestone, apply 2 tons per acre, and plan to apply more in 

 later years; but, if one cultivates less land and wishes to improve 

 it more rapidly, apply 4 to 10 tons of limestone per acre, and 

 it will give more marked results and will last much longer. 



