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Mineral mulch – a new moisture-saving frontier

Utilising mineral mulches, sourced on-farm, the Daws are boosting their crop yields
Photo: Evan Collis

While many growers are clay spreading to ameliorate difficult soils, Peter and Lena Daw at Ravensthorpe are spreading sand and gravel.

Peter classifies his soils as “different” as they are not typical for the area, being grey-brown and cracking with high pH, some sodic areas and gravel hills and knobs studding the country. Peter crops wheat, barley, canola and pulses in continuous rotation.

“We have a growing-season rainfall of around 292 millimetres and the water-holding capacity of these soils is good,” Peter says.

“We average around 1.8 tonnes per hectare for wheat and up to 5t/ha in good years, but water tends to either evaporate or percolate down the profile out of reach of crop roots. So we know we could achieve more.”

The Jerdacuttup River runs through the couple’s 3000ha property, which may partly explain the alluvial soil type and the presence of gravel.

Lena and Peter Daw are working with researchers from the Esperance Department of Primary Industries and Rural Development to learn more about the science and crop system benefits of mineral mulches. Photo: Evan Collis

“The river is a mixed blessing as we do incur periodic floods, like the one in 2017,” Peter says. The flood deposited sand across his cropping country.

Confronted with these deposits, Peter decided to spread the sand to make it thinner across his country and had an unexpected win. “We spread it with a grader at five to 10 centimetres in depth and sowed crops with knife-points with a two-inch splitter on the knife,” he says.

The yields of crops sown into this sand were 1.5 to 1.9t/ha greater than areas without the sand.

Realising that he had struck upon the potential of mineral mulches gave Peter confidence to then try gravel mulch, which he had readily available on the property.

He now has about three-quarters of a hectare treated with gravel mulch and is achieving similar yield gains to the sand mulch.

The beauty of the gravel is that it is inert, doesn’t absorb water and also doesn’t move as much as the sand, which can end up in the furrow.

“We have had the gravel mulch on this area going on five years now and continue to sow into it.

“Not only is it reducing evaporation, but it also appears to enable moisture to be retained closer to the surface, possibly through the insulating effect of the gravel.”

Peter has been working with senior researcher David Hall from the Western Australian Department of Primary Industries and Regional Development at Esperance – with GRDC support – to learn more about what is happening within these mulched systems to improve crop performance.

“It is great to get further insight into the science of mulching to not only validate this practice but also to learn how we can improve it,” Peter says.

Also read: Exploring the science of mineral mulch.

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