Yields climb as clay lessons learned
GroundCover™ Issue: 110 | Author: Nicole Baxter
John and Stewart Wallace are taking gradual but successful steps to improve their poor sandplain soils by lifting and spreading clay.
When John Wallace’s parents moved from Victoria in 1961 to take up land 35 kilometres north-east of Esperance near Neridup, Western Australia, they were hardly expecting that much of the land they cleared would turn out to be hostile to cropping.
The production constraint they discovered was water-repellent sand. Fast-forward to today and John Wallace says 70 per cent of the 4000 hectares he farms with his brother Stewart and their families is still water-repellent to varying degrees.
The non-wetting nature of the sandplain soils means weed germination is staggered, making pre-sowing knockdown control of weeds difficult to achieve. John says the problem has also hastened the development of herbicide-resistant weeds.
In non-wetting soils, radish, turnip and ryegrass are the most problematic. “You can have clean, absolutely magnificent cereal crops in June and if there’s a wet spring, by September they’ll be full of weeds,” John says.
To address the problem, John and his brother Stewart initiated a claying program eight years ago, targeting the worst of their sands in a bid to increase the clay content to five per cent.
Their first step is to locate a clay source within 1km of the treatment area. John says it is too expensive to open a pit any further away, which means a clay pit has been created within every paddock they treat.
While some growers employ consultants with electromagnetic equipment to locate a clay source, John uses a post-hole digger to probe the soil until a source is found, ideally within half a metre of the soil surface.
Initially, a contractor with a scraper was hired to collect and deposit clay onto non-wetting areas within paddocks. However, the contractor left the district, prompting John and Stewart to buy a 10-tonne scraper of their own. It is a step they have not regretted, allowing them to gradually work at ameliorating their problematic soils by treating about 100ha per year.
John and Stewart use yield maps to detect the lowest-yielding parts of the farm, which warrant treatment with clay.
Paddock inspections are done to confirm these results.
To treat the patches of non-wetting soil, clay collected in the scraper is laid out in strips across the soil surface at rates of between 150t/ha and 500t/ha, based on those yield results, with the poorer areas getting more clay.
The strips of clay are then spread (‘smudged’) using iron bars. Following this, a two-way disc plough is used to break down clods and evenly incorporate the clay across the treatment area.
Since claying about 800ha of non-wetting soil, John estimates the family’s crop yields have increased by about 1t/ha and weeds are now 50 per cent easier to manage.
Another benefit of claying, according to John, is a slight increase in the pH of the topsoil, which in addition to a program of applying 2t/ha of lime to his soils, is also helping to increase yields.
Aside from the benefits to crops, John sees claying as an excellent way to increase the survival and persistence of lucerne on the 20 per cent of the farm that is grazed.
Previously, he says, a lucerne stand would usually survive for only three years, but after adding clay, the lucerne persists for up to seven years.
In addition to claying, John and Stewart have also been trialling mouldboard ploughing on paddocks where clay is within 30 to 40 centimetres of the surface.
John describes the first 50ha they mouldboard ploughed as a “screaming success”, with wheat yields more than doubling from 1.7 to 3.5t/ha.
However, problems were encountered in the second year, when a legume pasture failed to germinate on the paddock, and the paddock had to be sown again. John says soil tests are pointing to boron toxicity as the probable culprit.
A further 80ha mouldboard ploughed in March 2013 looked like “a million dollars” until September, when 90 millimetres of rain fell and waterlogged the paddock.
“It went from looking like a 4t/ha wheat crop, to actually yielding just over 1t/ha,” he says.
“From putting my toes in the water with mouldboard ploughing, I now realise there needs to be more research done.”
To reduce costs and speed up the time it takes to ameliorate their non-wetting sands, John and Stewart plan to test a delving machine they bought several years ago, but until recently did not have the tractor power to pull it.
A delving machine has a massive chisel-like blade to lift subsoil clay to the surface. It requires a tractor with considerable power. For treatment to be effective, clay usually needs to be within 60cm of the surface.
Research is showing that delving machines can bring to the surface as much as 150t/ha of clay at a lower cost than opening a clay pit and then spreading clay on the surface.
Department of Agriculture and Food, WA, researcher Dr Stephen Davies has estimated the cost of clay spreading at $450 to $900/ha while he puts delving at $200 to $400/ha.
Using a tracked tractor for added traction, John and Stewart hope to treat at least 50ha a year, but they are aware they may need to hire a contractor to incorporate the clay with a spader.
“Adding clay to the topsoil by spreading or delving is really helping to improve the structure of our soils,” John says. “As custodians of our land, it’s nice to see that we can do things to make our soils better for the next generation.”