SOUTHERN NSW grain grower Peter Campbell has noticed increasing nitrogen levels after adopting stubble retention and direct-drilling.

He has also seen marked improvements in soil structure, biota and earthworms.

    AT A GLANCE
  • Who: Peter Campbell
  • What: cropping and sheep
  • Why: moisture retention
  • Where: Henty
  • Report: KIM WOODS

Peter and his wife, Alison, began retaining stubble about 15 years ago on their property at Pleasant Hills, near Henty, and now use strategic grazing as well.

The couple crop 900ha of wheat, triticale, canola and albus lupins, and run a self-replacing Merino flock joined to terminal sires.

Soils on the farm, which is located in a 525mm rainfall zone, range from red-brown loam to yellow podzolics on the lower country.

The Campbells have been direct-drilling crops since 1984.

They use a John Deere single-disc seeder on 19cm-row spacing, with furrow closers and press wheels.

Aricks wheels have been fitted to improve seeding depth when cereal stubble loads are heavy.

Strategic grazing is an important tool for Peter and Alison in managing stubbles.

Peter said a light graze equated to 500 dry sheep equivalents on 30ha for two weeks.

The first paddocks to be lightly grazed are those going back into crop, followed by those being sown to annual pasture.

Canola stubbles are not grazed and lupin stubbles are lightly grazed with young sheep.

Sheep are removed when either raised dust is seen or after rain.

Once the stubble paddocks have been grazed out, the sheep are shifted into two 8ha sacrifice paddocks and supplementary fed.

Peter has trialled several mechanical methods of stubble management, such as a stubble mulcher, harrows and residue collection directly from the header.

He said all had proven too labour and machinery-intensive.

This year, the spinners on the header were upgraded to achieve a better spread of residue across the width of the machine. But stubble retention is not without its risks and problems.

Foliar diseases such as yellow-leaf spot can carry over on cereal stubbles and rhizoctonia is a problem when using a disc seeder.

However, retaining stubble encouraged soil biota and earthworms, Peter said.

The Campbells' farm is a demonstration site for a cereal-stubble management project under the direction of Murrumbidgee Landcare and NSW Industry and Investment.

The project compares a range of stubble management practices in conserving moisture, providing ground cover and improving crop productivity.

NSW Industry and Investment conservation farming officer Tony Pratt said the project compared different seeding and tillage methods.

He said stubble retention practices aimed to conserve soil moisture from harvest to sowing. Demonstration sites were set up on 15 farms across four districts in southern NSW during 2008.

They are at Harden, Junee, Henty, Holbrook and Ariah Park. The systems include zero and minimum till cropping, with and without livestock.

Tillage machinery ranges from tine and disc seeders to air seeders and modified combines.

Tony said stubble management treatments included low cut at harvest, mulching, incorporation with stubble breakdown products, inter-row sowing, burning, baling and grazing.

Measurements were taken at harvest and pre-sowing on stubble height, ground cover, stubble load (tonnes/ha), soil moisture, soil-bulk density and soil-nutrient levels at different depths.

Stubble load, ground cover and plant populations (post-sowing) were measured directly behind the harvester and 3m to one side of the centre of the header track.

"Stubble retention has raised a lot of questions and hopefully this project will answer some of those," Tony said.

"There is no silver bullet to successful stubble retention for all farmers. This trial is raising more questions than answering them but it is all about promoting discussion among farmers."

At Henty and Pleasant Hills, autumn stubble burning had been a common practice but stubble retention is gaining favour.

"We are looking at stubble burning as a management tool rather than regular practice."

The three-year trial is evaluating grazing, harrowing, burning and the use of a biological residue breakdown product.

"At Peter Campbell's site we found a five to six tonnes/ha drop-off in stubble residue 3m to the side of the harvester," Tony said.

"Last year, stubble heights were 35-40cm and increased this year to 40-45cm.

"These heights are not so much an issue with a disc machine but anything above 45cm creates an issue for tine machines."

Tony said an "excellent" ground-cover figure of 100 per cent was measured behind the header.

Peter used spreaders behind the header which made a big difference.

Tony said 92-93mm of soil moisture had been conserved in this year's post-harvest period.

"A rough rule of thumb is half of that would be plant-available water," he said.

The Campbells' property is also a demonstration site for Henty Landcare's soil moisture and carbon-monitoring project.

Solar-powered, remote-sensing technology takes readings every 30 minutes under crop, pasture and native trees, down to a depth of one metre.

This data, plus rainfall measurements, are downloaded onto the Charles Sturt University's soil-moisture website.

The website is due to go live from September 13.

Tony said the stubble-management trial was providing tips and advice for all growers.

"Even the more progressive and earlier adopting growers are walking away with something new," he said.

"That might be just a simple thing such as adjusting a disc or an alternative spraying strategy."