Manures and Fertilizers 125 



common scab is likely to injure the tubers.^ The 

 powdery scab prefers acid soils and is reduced by liming. 

 There are other reasons which make the use of lime of 

 great value. The other crops of a potato rotation are 

 more likely to be benefited than the potato, and the net 

 profit of the rotation as a whole must be considered. The 

 clover and grass crops are the ones most benefited by lim- 

 ing, and these are the ones that do most to maintain the 

 soil supply of organic matter. Heavy sods and other 

 residues from hay crops bring up soil fertility rapidly at 

 small cost. In this way subsequent crops of potatoes are 

 benefited. Lime is also essential for the action of the 

 beneficial soil bacteria. Many American soils are now 

 becoming deficient in lime. Lime should be added to soils 

 in rotation in which potatoes are grown to as large an 

 amount as the soil can use without producing scab on the 

 tubers. What this amount will be can be found only by 

 careful trial on every soil and sometimes on every field. 

 Some soils can use several tons of limestone to the acre 

 without danger, while 500 pounds might be too much on 

 limestone soils or those in high condition of fertility. 

 Burned lime has been almost the only source of lime for 

 many years. Ground limestone is now coming into use 

 very rapidly, and it is probable that before many years will 

 entirely displace burned lime in most places. It is much 

 easier to apply and its use is safer. Burned lime is thought 

 by some to have a tendency to use up the organic matter 

 in the soil, even when thoroughly slaked before application. 

 Hydrated lime is too expensive to compare with the 

 others. Any form of lime should be applied to the crop 

 in the rotation which follows potatoes, and should be 

 thoroughly harrowed into the soil. 



' Vt. Bui. 184. 



