Reducing soil loss in shaded macadamia orchards

Saving soils in north coast macadamia orchards by kick-starting the planting of a selected groundcover called sweet smothergrass is the aim of a new three-year project.

The project is being carried out by NSW Department of Primary Industries (DPI) in collaboration with the Northern Rivers Catchment Management Board, Horticulture Australia and the Australian Macadamia Society.

"We will be substantially reducing the cost of adopting the groundcover for erosion control by making a new planting machine available to growers and facilitating the supply of smothergrass turf," said project leader Greg Reid from NSW DPI.

Previous NSW DPI studies have identified smothergrass as the most suitable groundcover for the low light environment in mature macadamia orchards, and highlighted the soil-saving benefits of groundcovers in macadamia orchards.

"However, adoption among growers has been limited due to the lack of suitable planting machinery," said Mr Reid.

Mr Reid said trials conducted over the last six years at Alstonville Centre for Tropical Horticulture and on nearby properties showed smothergrass establishes and spreads quickly, provides good groundcover in dense shade in old orchards and suits mechanical harvesting.

"A separate NSW DPI study showed that erosion was reduced by up to 99 per cent where groundcovers were established in macadamia orchards," he said.

"Soil loss from a mature macadamia orchard with shade-tolerant smothergrass growing on the orchard floor was less than half a bucket of soil per hectare per year."

NSW DPI extension horticulturist Kevin Quinlan said macadamia nuts can be harvested effectively from the smothergrass as long as the grass is mown after each harvest round to keep it short.

"The smothergrass growth slows significantly in winter so mowing is more important for harvest in the March to May period," he said.

Mr Quinlan said sweet smothergrass had to be planted as sprigs because the fertility of its seed was poor.

"Sprig planters are purpose built machines and to date none have been available or usable in a wide range of orchard situations.

"We have inspected a number of sprig planting machines in NSW and identified the critical features for a steep orchard design. We are negotiating to ensure that such a machine is available locally for the planting season next autumn."

Mr Reid said some macadamia growers had already started to establish sweet smothergrass on their properties from runners and had helped to develop planting rates and techniques.

"The groundcover establishes and thrives in low light situations where other grasses fail but it shows no tendency to choke other plants or native forest."

"We recommend planting parts of the orchard that are more susceptible to erosion and gradually increasing the area in a staged program over several years."

Media contacts: Greg Reid, NSW DPI, Wollongbar (02) 6626 1200, or Kevin Quinlan, Alstonville (02) 6626 2400.

Issued by: Phil Bevan, NSW DPI, Wollongbar Ph 6626 1350 or 0429 458 053