Cover crops care for sweetpotato soils

This is branded content for Department of Agriculture and Fisheries

SWEETPOTATO grower Brodie Wolfenden watched two very different scenarios play out on the hills near his property one wet day.

On a neighbouring block, water was running in sheets across the top of an "old-school" traditionally farmed paddock.

On his own block where soil structure and care have become the focus, the rain disappeared as it hit, soaking down into the paddock.

For Mr Wolfenden, the moment reinforced his decision from several years back to change his approach to sweetpotato production.

Operating under the Wolfies Farms brand about 30km north of Rockhampton at Rossmoya, Mr Wolfenden has about 202 hectares (500 acres) under cultivation with half planted to sweetpotatoes and the other half to a cover crop of jumbo sorghum.

Jumbo is an ultra-late flowering sorghum crossed to a sudan forage hybrid.

But it's not the product's grazing potential Mr Wolfenden is interested in.

Jumbo sorghum is able to suppress root-knot nematodes, a scourge of the Australian sweetpotato industry.

Once grown, the crop is mulched and left to sit on top of the soil to break down naturally.

The sorghum is left to reshoot and is often mulched a second time before the paddock is brought back into sweetpotato production.

ADOPTING cover cropping meant turning away from the traditional practice of spraying to achieve bare fallow ground.

"We would work up some paddocks and we would just get really hard clumps that we just couldn't break down," Mr Wolfenden said.

The cover crop means the rootzone is shaded, stays moist and the soil is being used to actively grow.

"Now when we cultivate it is soft, friable; it just breaks up in your hand most of the time," he said.

"You have a better transplant survival rate for your sweetpotatoes and your crop grows better."

The farm has seen yield increases as well. Wolfies Farms is in the rare position of being able to produce the popular Bellevue sweetpotato variety all year round.

The variety's own nematode resistance also adds to the defence against the soilborne pests.

"We are now able to grow the crop with no nematicides, which is fantastic," Mr Wolfenden said.

A multispecies cover crop was trialled but not maintained because of irrigation requirements to sustain it. Jumbo sorghum however is dryland grown.

"There's a lot of bulk in the jumbo as well so when we are mulching it leaves quite a thick layer on the ground," he said.

The cover crop practice has also improved the water infiltration and water holding capacity of the paddocks as illustrated when Mr Wolfenden watched the rain on the hills.

"It was a bit of a revelation," he said.

You know water infiltration is a sign of healthy soils and healthy soils improve water holding capacity in the paddocks, and you're not watching that run-off into the creeks and swamps downstream."

That means less sediment, nutrients, chemicals and fertilisers heading out to the Great Barrier Reef, something which Wolfies Farms has gone the extra effort to ensure by becoming the first sweetpotato growers Reef Certified through the Hort360 accreditation process.

Agronomists from the Queensland Department of Agriculture and Fisheries (DAF) are working with growers on the utilisation of nematode resistant cover crops to provide biomass and optimise fertiliser use, as well as retaining nutrients on farm and enhancing soil health.

They are also working with growers to identify ways to reduce chemical use and reduce in-field and edge of field erosion.

Mr Wolfenden utilises trickle irrigation taken from their ring tank dams which are fed by a creek on the property.

"When it rains up in the hills, it flows down our little creek and we capture some of that flow in storage dams," he said.

"Our creek is not a reliable source as far as everyday irrigation goes."

Controlled traffic through GPS guidance ensures further care of the paddocks and soil.

"The aim of controlled traffic is that at any time in the future, say 50 years time, the growing rows in the paddocks have never been driven on and you have zero compaction," Mr Wolfenden said.

"Combined with the cover cropping we should have some nice soft soils."

Mr Wolfenden works the property alongside his father, Rodney, a well-known figure within the Australian sweetpotato industry.

He was integral in setting up Australian Sweetpotato Growers, the national body which helps with promotion and research.

Wolfies Farms sends to all the major wholesale markets in Brisbane, Sydney, Melbourne, Adelaide and Perth.

Brodie Wolfenden said the team on the ground was critical in making it a success.

"We have some really great staff who help us keep improving and expanding," he said.

"Everyone is very important in their own right and if you take a few people out of the system, it would suffer."

The learning has not stopped for the Wolfendens.

Mr Wolfenden said he is currently trialing a soil ameliorant with organic compounds to better utilise fertilisers.

He is also in the stages of implementing a more complete integrated pest management program with beneficial insects helping to further reduce pesticide use on the farm.

There certainly is an ongoing progressive pathway towards more sustainable sweetpotato production with improved water quality outcomes thanks to the work of Wolfies Farms, agronomists and DAF.

This is branded content for Department of Agriculture and Fisheries