Agroforestry for the Brigalow floodplain

Trees have the potential to help reduce erosion and drainage, control spray drift, provide natural habitat for native animals and maintain biodiversity - as well as long-term potential for timber harvesting. The possibilities challenged a number of brigalow soil farmers on Queensland's Darling Downs to rethink their approach to trees on their farms.

The following is an edited version of a recent FARMSCAPE report.

FARMSCAPE stands for - Farmers, Advisers, Researchers, Monitoring, Simulation, Communication and Performance Evaluation. It is about agricultural knowledge, both practical and scientific. These two ways of seeing farming meet in FARMSCAPE when a farmer 'does an experiment' using a scientific model made to look like an actual paddock of his/her farm and, as a result, alters practice (or decides not to).

FARMSCAPE is an approach to farming systems research that combines:

  • on-farm monitoring to ensure local relevance
  • computer simulation to feasibly explore alternative management possibilities
  • discussion that combines the perspectives of farmers, advisers and researchers.

FARMSCAPE developed the assessment tools for the trees on-farm project described here.

RESEARCH INTO the costs and benefits of strip-planting trees beside broadacre crops was sparked after a Landcare group on the Brigalow Floodplain began planting trees to reduce erosion in 1996.

Brigalow producers on the western Darling Downs, led by Nevin Olm and Jeff Bidstrup, have planted more than 75,000 trees in the catchment.

"We wanted quick-growing trees with the potential for agroforestry," Mr Bidstrup said. So far the species used in the models have been forest timbers such as Pinus radiata (Radiata pine), Eucalyptus globulus (Tasmanian blue gum), E. grandis (Flooded gum), and E. argopholia (Western white gum).

"The reduction in crop yield (along the edge) is weighed against a potentially higher overall yield of the crop, because of the trees forming a windbreak and reducing wind damage," Mr Bidstrup said.

An increasingly important added benefit is that strips of trees on the downwind side of the property reduce pesticide spray drift onto neighbouring properties and trees on the upwind side form a barrier against spray drift from other farms.

At 'Prospect', a 1,600 ha cotton, grain and pulse property in the family since 1908, the Bidstrups minimised the loss of yield by planting trees alongside the roadway, so that only one side of the treeline influenced the crops.

"Thankfully the generations before did leave some strips of trees, so we only needed to add strategic plantings," he said.

CSIRO researcher Perry Poulton is using the Brigalow properties to validate simulations for the APSIM (computer) model to investigate the trade-off between trees and crop productivity.

(Mr Poulton explained that APSIM (Agricultural Production Systems Simulator) is "like a flight simulator". Just as a flight simulator lets you explore the challenges of flying from the safety of the ground, APSlM lets you explore the possibilities of your agricultural system from the safety of your computer screen.)

Dry weather at the end of the winter 2000 cropping season allowed researchers to accurately measure how far tree roots invade crops, compete for water and nutrients during the growing season or reduce the effectiveness of a fallow. Soil-water studies showed that, through a summer fallow, tree competition reduced plant -available water at the edge of the paddock for a distance of up to three times the height of the trees.

Take-up of agroforestry has been slow but, Mr Bidstrup says, farmers are waiting to see if agroforestry proves to be profitable, and if so, what species of trees are best suited to different areas.

"We went ahead because we like to see trees. It will be a few years before we see if the value of the trees was worth the effort."

Recent farmer discussion groups used output from APSIM agroforestry tools in constructing an economic framework for evaluating annual costs and benefits associated with agroforestry as part of the overall farming enterprise.

Mr Poulton said future research with farmers will focus on management of the competition zone, planting densities, thinning frequency and other management options to yield the best possible economic and environmental benefits to producers.

Contacts: Mr Perry Poulton 07 46881202 Mr Jeff Bidstrup 07 4668 1118 Mr Nevin Olm 07 4665 2206

Region North