Soil 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 profiles. Understanding the freezing and thawing processes and their effects on water movement and soil structure is necessary to develop improved 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 packed 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 were buried vertically in the field and exposed to the winter freeze/thaw conditions at Ankeny, Iowa. Soil columns were removed from the field throughout the winter and sectioned into 0.05-m layers. Each layer was analyzed for water content, bulk density, and electrical conductivity. Water moved upward to the freezing zone, carrying some solutes along. Electrical conductivity values verified the movement of solutes during the freeze/thaw periods. Bulk density changed abruptly as a result of expansion and compression of the soil matrix during freeze/thaw periods. Thawed soil retained some of the physical property changes caused by freezing and remained more variable than unfrozen soil. Freezing action increases the heterogeneity of soil properties in the frozen zone. This additional variability increases the complexity of predicting overwinter changes in the soil profile and the difficulty of developing management practices for maximizing nutrient efficiency while minimizing pollution.