Freeze-Drying Effects on Wet and Dry Soil Aggregate Stability

Freeze-drying of soil aggregates may reduce aggregate size and increase erosion potential. We investigated whether freeze-thaw frequency, water content, and initial aggregate size influences the freeze-drying disruption of soil aggregates, as measured by dry and water-drop-impacted wet sieving. Aggregates of two western Minnesota soils, Barnes loam (a fine-loamy, mixed Udic Haploboroll) and Hamerly clay loam (a fine-loamy, mixed, frigid Aeric Calciaquoll) were tested. Vulnerability to wet sieving was increased much more by freeze-drying than was vulnerability to dry sieving. Freeze-drying decreased wet aggregate stability in 85 of 96 cases and dry aggregate stability in 56 of 96 cases. Initial water content largely determined whether freeze-drying decreased aggregate stability. For water contents of 0.05, 0. 15, 0.25, and 0.35 kg kg -1 , the mean weight diameters (water-drop-impacted wet sieving method) of freeze-dried aggregates were 93, 64, 48, and 46%, respectively, of their non-freeze-dried values. For dry sieving, values for the same four water contents were 100, 103, 90, and 88%, respectively. The detrimental effects also generally increased as aggregate size increased. Freeze-thaw frequency and soil type had less effect on freeze-drying disruption than did water content and initial aggregate size. Thus soil surface resistance to breakdown by freeze-drying and raindrop impact would be expected to decline as initial aggregate size and soil water content increases