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Lime [calcium carbonate (CaCO3)] has been used for acid soil amelioration of acid soils in Australia and elsewhere, but its effects on soil physical properties are not clear. Mechanisms responsible for the beneficial changes in the soil physical and structural properties of an acidic hardsetting soil in southern NSW, Australia, as a result of lime application were investigated. Changes in water-stable aggregation, a mechanical property, were related to changes in physicochemical properties, and soil organic carbon forms as a result of liming. The improved soil structure due to liming can be explained in terms of reduction in SAR (Sodium absorption ratio) and increase in EC (Electrical conductivity) (both lead to less dispersion) as well as increases in labile carbon (less slaking). The combined effects of reduced dispersion and slaking were responsible for the reduced bulk density and tensile strength of the hardsetting surface soil. These beneficial effects of liming on soil structural and physical properties were detectable 4 years after but not 18 years after lime application. [ABSTRACT FROM AUTHOR]

Acid soils threaten agriculture in Australia as well as in many parts of the world by reducing plant productivity. Surface-applied lime (CaCO3) moves into the root zone only slowly but the process can be considerably hastened in the presence of earthworms. In a laboratory experiment, the abilities of three earthworm species in incorporating lime into the subsoil and the mechanisms involved were investigated. Aporrectodea longa was the most effective in moving surface-applied lime, increasing subsoil pHCa by 1.1 units (from 4.0 to 5.1) in the 7.5–10 cm layer after only 6 weeks. Aporrectodea trapezoides and a native anecid, Anisochaetae sp., were less effective than A. longa, but still increased pHCa by 0.7 unit in the 7.5–10 cm layer. The extent of lime incorporation by the different earthworms was unrelated to burrow size and abundance, but significantly related to the increase in water stable aggregates (>250 μm) found in the earthworm-inoculated soils. The water stable aggregates, largely in the forms of earthworm casts and burrow wall material (drilosphere) had significantly higher pH (>6) than the bulk soil (4.0). The results suggest that significant amounts of surface-applied lime can be carried down the soil profile by the earthworms either via ingestion and subsequent deposition as casts at depth or by directly attaching to the body surface. [ABSTRACT FROM AUTHOR]