Freezing effects on aggregate stability of soils amended with lime and gypsum

Aggregate stability, which influences soil response to raindrop impact and other erosive forces, is affected by freezing. We hypothesized that lime or gypsum added at agriculturally feasible rates may act as bonding agents to mitigate the effects of freezing on the stability of aggregates from different soils. Thus, the objectives of the laboratory study were to determine the effects of freeze-thaw cycles, water content at freezing, and lime and gypsum additions on the aggregate stability of six soils differing in texture, mineralogy, and organic matter. To all samples but the control, either CaCO3 or CaSO4 - 2H2O was added at a rate of either 0.2 or 1.0% by weight of oven-dry soil. Field-moist aggregates were vapor-wetted to either a low water content (5-10% w/w) or a high water content (25-30%), then frozen and thawed either 0, 1, or 3 times in brass cylinders. After thawing, they were vapor-wetted to 0.30 g g-1 and their stability was characterized by wet sieving. For all soils, aggregate stability decreased significantly with increasing water content at freezing. When averaged over bonding agents and addition rates, soils commonly increased in stability, at times significantly, after one freeze-thaw cycle. Soils with clay contents of 20% or more and organic matter contents over 3% were the most stable after freezing. When averaged over soils and freeze thaw cycles, aggregate stability was not affected by bonding agents at low water contents. At high water contents, however, stability increased significantly (P