Landscape rehydration. The impact on soil health.
Visually, the positive impacts of landscape rehydration works implemented in south-west Queensland are clear. But what impact do these works have on soil condition?
Natural Resource Management group, Southern Queensland Landscapes, has been supporting a growing number of graziers across the region implementing works to restore and rehydrate the landscape. These works spread the flow of water over the landscape and slow its velocity, reducing soil loss, repairing erosion and leading to increased infiltration. The visual effects of these works are striking. Often after just a single rainfall event, scalded floodplains and erosion features commence the process of healing themselves, with the rapid establishment of grasses and other pasture species.
Soil microbiologist Dr Elaine Gough’s UniSQ-funded project “Soil biological diversity improves landscape resilience to drought” is seeking to identify what impact landscape rehydration works have on soil health. The project will compare the differences in soil microbiology, with a focus on nematodes, mycorrhizal fungi and rhizobacteria between control (claypans) and treatment sites at three stations in the Eulo district (70km west of Cunnamulla in South West Queensland).
As part of the project, and in my role as the SQNNSW Innovation Hub’s Regional Soil Coordinator, I collected soil samples at each site for soil chemical analysis as well as taking infiltration measurements as an indicator of soil physical condition, supported by Christine Crafter a Project Delivery Officer from Southern Queensland Landscapes.
In terms of both vegetation and soil structure across each station, it is obvious that the landscape rehydration works have made a substantial positive difference. Christine noted that the treatment sites were “rain ready” due to the established vegetation and cracks present in the soil.
Infiltration was measured using automated mini disk infiltrometers, to determine what is known as “near saturated hydraulic conductivity”. The results between the control and treatment sites were the biggest difference in soil condition, with increases in infiltration capacity being three, five and 11 times greater than that of the paired control site.
Soil organic carbon (SOC) is critically important for soils to function effectively, particularly in the Rangelands where SOC is naturally low. Building SOC is a slow process largely dependent upon rainfall/moisture as well as grazing management. The soil test results indicate that there was a measurable increase in SOC in the top 10cm on two of the three stations.
Sodic (soils containing a lot of sodium which can cause clay particles to disperse, resulting in degradation in soil structure) and saline (soils containing a lot of salt) soils are common in the south-west of Queensland. The control sites at all three stations were no exception. An interesting finding was that at two of the three stations, the level of both sodicity and salinity were substantially lower in the treatment sites. This suggests that the increased detention time of overland flow resulting from the landscape rehydration works is having the effect of leaching salts through the soil profile down to at least 50cm, providing a more hospitable environment for plant growth.
Across much of south-west Queensland, and the Rangelands more broadly, the condition of the landscape has deteriorated markedly since the arrival of Europeans. The consequences of landscape modification, combined with drought, has fundamentally changed the hydrology of the landscape; increasing runoff, soil loss and creating erosion features that have led to dehydrated landscapes. Work such as this being carried out by UniSQ researchers, graziers and on-the-ground NRM practitioners can help us understand how to best reverse this damage.
For more information, contact Regional Soil Coordinator Cameron Leckie: Cameron.Leckie@usq.edu.au
The SQNNSW Hub Regional Soil Coordinator is supported by the Australian Government's National Landcare Program.