Attributes of Tasmanian ferrosols under different agricultural management

Abstract

Attributes of 25 Tasmanian ferrosols under 5 forms of management (low-input pasture, high-input pasture, intermittent cropping, continuous cropping, and pyrethrum production) were assessed using field and laboratory techniques, to see how these attributes changed as the intensity of land management increased. Among the most notable changes were soil organic carbon (C) in the top 150 mm, which was about 30% less in cropping and pyrethrum paddocks than pasture paddocks, and microbial biomass C, which was about 60% less. Earthworm numbers showed even greater differences, with virtually no earthworms under pyrethrum. Pasture soils had higher shear strength and water contents at the liquid limit in the top 150 mm, and more water-stable aggregates in the subsurface soil. Despite these differences, the absolute values of most attributes in cropping paddocks were of a magnitude, which suggests that Tasmanian ferrosols even under continuous cropping are still in good condition. This agreed with the views of the farmers, obtained by individual survey. The decrease in organic C in the cropped soils has not decreased the effective cation exchange capacity, probably because their higher pH due to liming has compensated. Because ferrosols with organic C contents of 1−2% elsewhere in Australia have been shown to have serious management limitations, we need to know by how much the organic C contents in Tasmanian ferrosols will continue to decrease under intensive cropping to predict whether they might suffer in a similar way.