Freeze‐Drying Effects on Wet and Dry Soil Aggregate Stability

Abstract 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.