A laboratory study of the residual influence of some amendments on the reconsolidation of disturbed Salisbury silt loam

The residual effect of various soil amendments on the reconsolidation of a strongly acidic Salisbury silt loam C horizon which contained 0.25% free aluminium was investigated in the laboratory. Limestone (CaCO₃), gypsum (CaSO₄) and peat moss were added at 0.5, 0.08 and 2.0% (w/w), respectively. In a fourth treatment, CaCO₃ (0.5%, w/w) was added 24 months previously. Results from these treatments were compared to those from an untreated control. All soils were redisturbed to simulate tillage. The soils were subjected to a standard Proctor test and a low-energy compaction test designed to simulate a 0.44 m soil overburden. Penetrometer studies were performed to examine soil strength.

The mineralogy of the Salisbury C-horizon was dominated by illite, with lesser amounts of chlorite occurring; kaolinite and vermiculite were present only in small amounts. Application of peat lowered the maximum dry density of the Proctor test and increased the concomitant optimum moisture content. Soil chemical amendments had no effect on compaction as measured by the Proctor test, but significantly increased the dry bulk density in the low-energy compaction test. Hence volumetric moisture content, at a moisture tension of 101 kPa, was increased by the chemical amendments. Soil strength, as measured by the cone index at a constant soil moisture tension, was decreased by the chemical amendments; however, after correction for volumetric moisture content, no treatment effect occurred. The chemical amendments significantly decreased the concentrations of inorganic and organically bound Al and inorganically bound Fe.

The results of the low-energy compaction test suggest that application of gypsum or limestone amendments to severely disturbed, highly acidic soils, which contain appreciable amounts of aluminium oxides and exchangeable aluminium, may increase the soil's propensity to reconsolidate. This was not revealed by the standard Proctor test.