Scattered paddock trees, litter chemistry, and surface soil properties in pastures of the New England Tablelands, New South Wales

Abstract

Scattered paddock trees are widespread throughout rural Australia but their effect on soil conditions has received only limited research attention. This study investigated the influence of 3 'Eucalyptus' species on surface soil properties on different parent materials at both stocked and unstocked sites on the Northern Tablelands of New South Wales. Mineral soil samples to a depth of 5 cm were collected at intervals up to twice the canopy radius away from tree trunks and litter samples were collected at corresponding points. Mineral soils were analysed for pH (CaCl₂), organic carbon (C), and extractable phosphorus (P) concentration, while for the litter samples, P, sulfur, cations, and ash alkalinity were determined. Stocking with sheep and cattle increased surface soil acidity and C and P concentrations at each location. However, soils under 'E. melliodora' and 'E. viminalis' showed higher pH and increased C and P concentrations close to the tree stem irrespective of grazing. Soils under 'E. caliginosa', while having similar patterns of C and P, showed variable acidity patterns with instances of lower pH close to the tree stem. Spatial patterns in soil acidity were associated with the ash alkalinity of litter, indicating litter as a source of alkalinity addition to the soil surface, although different patterns of soil pH could not be fully explained by litter ash alkalinity alone. The close correlation of litter Ca content with ash alkalinity suggests that this element might be a suitable indicator of the acid amelioration capacity of different tree species.