Fertility rundown in sown grass pastures is a widespread problem in Queensland, with an estimated cost to industry of more than $17 billion during the next 30 years.
It results in less vigorous, less productive pastures with a lower basal groundcover and increased bare ground, leading to increased run-off and soil erosion. The decline in vigour of the pasture also results in lower competitive ability and the subsequent invasion by unproductive grasses and weeds.
In the Maranoa-Balonne, the Queensland Murray-Darling Committee has worked to demonstrate the importance of nutrients on the health, groundcover and production of rundown pastures to local landholders.
This work was part of a Landcare Sustainable Practices project that aimed to deliver increased landholder engagement and adoption of sustainable and innovative natural resource management practices by primary producers. This project is supported through funding from the Australian Government’s Caring for our Country initiative and contributes to the sustainable farm practices national priority area.
Working on the Plant family’s “Tregona” in the Glenmorgan district, QMDC Grazing Lands Management Officer Dr Sid Cook investigated the impact of nutrients on the productivity of their rundown pastures.
“Since the early 90s they have noticed their pastures growing less vigorously, leading to a decline in their stock carrying capacity, particularly during dry periods,” Dr Cook said.
“Research has shown that fertility rundown in long term sown grass pastures is caused by nitrogen and other nutrients becoming tied up in soil organic matter, roots and crowns of old grass plants.
“The decline in production contributes to over grazing, a reduction in crown size and overall cover of the grasses, leading to reduced resilience and often death during drought. If allowed to continue, scalds can develop on soils that surface seal or are hard setting allowing both wind and water erosion to occur, leading to land degradation.”
Dr Cook said the Plants hoped the trial, which was designed in late 2009, would answer some of the questions relating to the amounts of nitrogen required for sustainable production, as well as investigating whether phosphorus played any role in the rundown of buffel grass pastures.
He said the trial involved varying rates and repetition of nitrogen and phosphorus, ranging from zero on the control plots through to 120 kilograms of nitrogen per hectare.
“Aided by good summer rainfall from the time the fertiliser treatments were first applied, the pastures responded strongly to the application of nitrogen fertiliser,” Dr Cook said.
“Between January and April 2010 nitrogen-fertilised plots produced between 5,083 and 7,887 kilograms of dry matter (DM) more than the non-fertilised control plots. When allowances are made for wastage and a minimum residual of 1,000 kilograms of DM per hectare, this equates to an extra 234 and 410 grazing days, respectively.”