246 



THE PRINCIPLES OF SOIL MANAGEMENT 



soil and consequently the crop is lifted. Shallow-rooted 

 crops are gradually raised out of the ground by repeated 

 freezing when wet, because the soil settled back into 







:; . -'' jl. wtfaa 



' _* 





Fig. 79. Alfalfa roots raised out of the soil ("heaved") by the repeated 



freezing of a wet clay. 



place more quickly than the root. Not only is the plant 

 lifted out of the ground, but many of the smaller roots 

 are broken off, all of which greatly reduces the vitality 

 of the plant. It is most serious on clay soil, because this 



