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through the soil, the ice will continue to grow, until most pores 

 are filled with ice and the formation of ice lenses begins. The 

 overlying soil is pushed up while the ice lens is expanding. 

 Most injury to the plants occurs at this time. The roots are locked 

 in the frozen soil clods and when an ice lens is forming between 

 the clods, it pushes the aggregates apart with a force much greater 

 than the strength of the roots, resulting in breakage of especially 

 the smaller roots. The tree loses part of its anchorage and is 

 pushed up with the overlying soil by the growing ice lens, or 

 more likely, a combination of several such lenses. When the weather 

 warms the following spring, some of the surrounding soil may fill 

 the cavity left by the ice lens while the tree remains uplifted, 

 thereby exposing the roots. This may result in drying-out of the 

 roots or injury by subsequent cold temperatures. 



The immediate cause of frost heaving is excess moisture, but 

 a soil does not always have to be excessively wet to be prone to 

 heaving. Dirksen and Miller (1) in a series of laboratory experi- 

 ments found that water lost from the unfrozen soil enters the frozen 

 soil and causes its ice content to increase. This transport of 

 water occurs even when the soil is frozen, through thin liquid 

 water films associated with the ice surfaces. These researchers (1) 

 concluded that when ever the soil was about 901 saturated, ice 

 wedge formation and thus heaving could be expected. 



The practical implication for the fruit grower is to provide 

 adequate soil drainage. When the soil is kept sufficiently dry 

 the movement of water in the soil is reduced and ice lens formation 

 and subsequent frost heaving can be prevented. Sometimes, such as 

 during the 1978-79 winter, the weather conditions may be so adverse 

 (e.g., rainstorms during short, warmer periods in the winter) that 

 significant wetting of the profile occurs and frost heaving results. 

 If the grower suspects that such root injury occurred, measures 

 such as extra pruning should be taken to balance the above-ground 

 vegetative parts with the reduced root system. This will be 

 especially important when the growing season following the winter 

 injury has lower than average rainfall and thus puts an extra 

 demand on the already strained root system. 



The extent of the root injury also depends on the soil texture. 

 Sandy soils drain quickly, have a lesser capability to utilize 

 water and are therefore less susceptible to winter injury. The 

 finer textured soils are generally more prone to frost heave damage. 



Fortunately, the winters in Massachusetts are rather cold with- 

 out too many warming cycles in January and February and significant 

 root injury due to frost heaving most likely will remain the excep- 

 tion rather than the rule. 



References 



1. Dirksen, C. and R.D. Miller. 1966. Closed-system freezing of unsaturated 



soil. Soil Sci. Soc. Amer. Proc. 30:168-173. 



2. Russell, W.E., F.J.D. Smith, E.T. Bingham, and R.M. Soberalske. 1978. Frost 



heaving in alfalfa establishment on soils with different drainage char- 

 acteristics. Agron. J. 70:869-872. 



