Bare is not a good look for visiting soil expert
GroundCover™ Issue: 59
Australian farmers are advised that permanent cover is the way to overcome the no-till plateau, reports Brendon Cant
Too much bare soil spoilt Rolf Derpsch"s view when he was travelling 3700 kilometres along WA roads earlier this year as part of his six-week tour of WA and SA.
Hosted by the WA No-till Farmers Association (WANTFA), with support from the GRDC and the Australian Government"s National Landcare Sustainable Industries Initiative, the world-renowned Paraguayan no-till expert met with growers, researchers and agribusiness to analyse Australian no-till practices.
"Australian growers have reached a plateau in terms of no-till and won"t enjoy maximum benefits until their soil is permanently covered," Mr Derpsch said. "Carbon content is the most important parameter determining soil quality as it alleviates structural, nonwetting and nutrient uptake problems.
"To substantially increase carbon content, baling and burning of stubble must be abandoned and sheep locked out of cropping paddocks."
In 20 years of no-till, Brazil"s soybean yields increased 50 per cent, while fertiliser use halved. Meanwhile, corn yields doubled and 30 per cent less fertiliser was applied.
"To reach full sustainability, at least three tonnes of stubble per hectare is required," Mr Derpsch said. "This is achieved by including cover crops, changing from tynes to discs and diversifying rotations. Continuous soil cover keeps soil temperatures below 35 degrees Celsius, ensuring improved microbial activity and better nutrient cycling."
At the GRDC-funded Meckering site, WaNTFA trialled suitable cover crops, such as annual legumes, and pastures, brassicas, grasses and broadleafs, such as sunflowers, for inclusion in wheatbelt rotations.
WANTFA"s scientific officer, Dr Ken Flower, says sowing time is a key factor in how well cover crops produce biomass and control weeds. "Saia oats (Avena strigosa), Oriental mustard (Brassica juncea) and French serradella showed good potential in our 2005 trials. Cover crops, such as Saia oats, produce a large amount of residue.
"Bill Porter, Department of Agriculture, is running trials at Meckering testing Saia oats" ability to accelerate liming movement down the soil profile."
At WaNTFA"s 2005 Meckering Spring Field Day, Mr Derpsch explained how Brazilian growers used a double disc system, with 34-centimetre (15-inch) front and 29cm (13-inch) back discs rotating at different speeds to self-clean.
"The front wheel"s weight cuts through residue, the second wheel furrows and the rear rubber press-wheel closes," he said. "Planting east-west decreases weed biomass, as shading by the crop occurs."
Disc benefits, such as a 14kmh working speed, halving fuel costs, reducing weeds and better handling of high residues, were highlighted by a five-grower panel at the field day.
Mr Derpsch and DR Flower visited the south coast of Wa, where growers have seen Rhizoctonia in canola and take-all in wheat disappear and yields increase by between 50 to 100 per cent since they adopted no-till in 1996.
Mr Derpsch reported that soil could not be seen through the residue and increased organic matter had reduced nonwetting soils in all crops, except lupins.
They also visited Jim and Chris Kirkwood"s property at Kendenup, Wa, and saw discs successfully used in stony paddocks, after raking and removing large stones. Chris Kirkwood said: "I plan to use soft-seeded oil radish to aerate soil and introduce more oilseeds and cover crops in shallow clay areas to increase soil aeration."
Mr Derpsch explained that plants biologically prepare soil by loosening it with their roots, forming pathways for the next crop. "We"ve used blue, yellow and white bitter lupins successfully in South America, as they can have 1.2 metre-long roots and alkaloids in their leaves prevent insect feeding."
DR Flower concluded that conditions in WA were unique. However, by investigating no-till techniques around the world, WA growers and researchers could learn and adapt, progress to more sustainable no-till and enjoy greater benefits.
Dr Bill Porter talks to growers about the potential of Saia oats as a liming accelerant at the recent Meckering Spring Field Day. Photo: Brendon Cant
Cover-crop trials at the GRDC-supported WaNTFA site at Meckering. Photo: Brendon Cant
GRDC Research Code WaN00003
For more information: DR Ken Flower, 08 9622 5584, 0427 000 729
Region North, South, West