STUDIES ON FREEZING AND THAWING SOILS IN IOWA

摘要

Frozen soils have a major influence on the cropping systems and farming practices in northern states. However, relatively little research has been done on the physical, chemical, and biological processes that occur in the field during the non-growing season. Experiments on frozen soils were started recently in Iowa to 1) study the effects of residue cover on soil freezing and thawing, 2) measure the movement of water and solutes and changes in soil structure due to freezing and thawing of repacked soil columns in the field, 3) test the SHAW (Simultaneous Heat And Water) model for its capability to predict freeze/thaw cycles, and 4) determine the effect of freeze/thaw and wetting/drying cycles on soil cracking. Residue cover changed freeze/thaw rates and frost depth. Water moved to the freezing front which resulted in a net upward movement after thawing. Solute movement was more complex because of its movement with water, its exclusion from water during freezing, and its redistribution during and after thawing. The SHAW model provided reasonable agreement with measured frost depth during the winter of 1993-1994. These studies are continuing and will aid in the development of management practices to protect our soil resources while sustaining a productive agriculture.