Taking Action on Subsoil Acidity in Harden
HMLG were one of the first landcare groups in Australia to identify soil acidity as a limiting factor to productivity, and begin soil testing to understand its distribution. Because of this work, soil sampling and testing has now become standard practice in land management today.
Subsoil acidity was identified in the early 1990’s as a major cause of poorer performing paddocks in the Harden area. HMLG sought to assess the extent of the subsoil acidity problem in the region by soil sampling. As part of this survey, we also investigated if there were more easily measured, local indicators of subsoil acidity.
In April 1999, soil samples were collected in 270 paddocks at three depths (10 cm, 20 cm and 30 cm) on 48 farms located within a 40km radius of Harden. Samples were analysed for soil pH and exchangeable cations (Al, Ca, Mg, K and Na).
Close to 75% of the sites sampled had a soil acidity problem at some depth in the soil profile
For at least half of those, the soil was acidic below 10 cm, but not in the top 10 cm. This finding demonstrated a clear need for subsoil testing. In terms of soil amelioration, there was no evidence that the application of lime to the 0 – 10 cm layer had any effect on the acidity of the deeper soil layers.
This project successfully demonstrated to the Harden and broader landcare community the need for subsoil acidity to be explored as a limiting factor to productivity, as well as the utility of soil sampling for informing land management decisions.
Results showed that subsoil acidity is a prevalent problem in the high rainfall cropping area of Harden Shire, despite over a decade of expanding lime usage. Greater lime input is likely required to sustainably manage acid soils in the region.