SORE WATER AND SOLUTE MOVEMENT AND BULK-DENSITY CHANGES IN REPACKED SOIL COLUMNS AS A RESULT OF FREEZING AND THAWING UNDER FIELD CONDITIONS

Freezing and thawing affect water and nutrient movement within soil pr ofiles. Understanding the freezing and thawing processes and their eff ects on water movement and soil structure is necessary to develop impr oved management strategies. Experiments were conducted to measure the effects of freeze/thaw on soil water and solute movement in a Webster silty clay loam (fine-loamy, mixed mesic Typic Haplaquolls). Polyvinyl chloride (PVC) cylinders (0.13 m inside diameter, 1.2 m long) were pa cked with topsoil, and potassium bromide tracer was placed in the top 0.05- to 0.15-m soil layers in some of the columns. The soil columns w ere buried vertically in the field and exposed to the winter freeze/th aw conditions at Ankeny, Iowa. Soil columns were removed from the fiel d throughout the winter and sectioned into 0.05-m layers. Each layer w as analyzed for water content, bulk density, and electrical conductivi ty, Water moved upward to the freezing zone, carrying some solutes alo ng, Electrical conductivity values verified the movement of solutes du ring the freeze/thaw periods. Bulk density changed abruptly as a resul t of expansion and compression of the soil matrix during freeze/thaw p eriods. Thawed soil retained some of the physical property changes cau sed by freezing and remained more variable than unfrozen soil, Freezin g action increases the heterogeneity of soil properties in the frozen zone. This additional variability increases the complexity of predicti ng overwinter changes in the soil profile and the difficulty of develo ping management practices for maximizing nutrient efficiency while min imizing pollution.