Crop roots push deeper after lime
GroundCover™ Issue: 109 | Author: Nicole Baxter
With subsoil acidity taking a large bite out of growers’ profits every year, one farming family is taking determined steps to arrest this drain on business returns
Tony White used to think rainfall was the main constraint to crop productivity on the property he farms with his brother Paul and father Brian near Miling, Western Australia, but after two years of lime incorporation he now sees things differently.
For the past two seasons, Tony has harvested more grain by doubling his usual rate of lime and using spading and mouldboard ploughing to really drive the ameliorant into the subsoil.
Soil types on the White family’s farm range from shallow red loams to heavy clays and yellow sands, with tests showing the yellow sands are the most acidic, especially at depth.
Tony says the light-bulb moment for increasing his lime use came in 2007 after two dry seasons. At that time, he says, his neighbours were achieving higher yields, even though all other operations, rates, timings and varieties were similar.
“The only difference was they had a road train and were going to the coast in summer and bringing back lime,” he recalls. “That’s when it clicked, and since then we have been carting lime from the coast too.”
Although Tony had always applied one tonne per hectare of lime, which at the time was the rate suggested by consultants if it was affordable, he now has empirical evidence from amelioration works on his property that the rate he was applying was not enough.
Soil tests done by Joel Andrew at Precision SoilTech show the surface pH (0 to 10 centimetres) was adequate at 5.5, but the subsoil (10 to 30cm) was too acidic at 4.0, less than the Department of Agriculture and Food, WA (DAFWA), recommended minimum of 4.8.
In response Tony set up a trial on his property in 2012 as part of the Miling–Moora Pasture Improvement Group (MMPIG).
He applied 3t/ha of lime and hired a contractor to incorporate the lime to a depth of 30 to 40cm using a spader. Tony asked the contractor to leave a strip unspaded so researchers could check if there were any differences in wheat root depth.
In early November 2012, Mr Andrew and DAFWA’s Chris Gazey dug a soil pit as part of their research for a ‘Caring for our Country’ soil acidity project and used the pit as a learning opportunity for members of the MMPIG.
Mr Gazey, who now has a five-year GRDC research project to further investigate the impact of soil acidity on grain yields in WA, says using a spader to incorporate the lime provided pathways of better pH or less aluminium toxicity, which allowed wheat roots to more thoroughly explore the soil profile in search of nutrients and moisture (Figure 1).
“Roots in the non-spaded area could only penetrate to 23cm, but there was significant moisture available further down the soil profile. The crop in this area yielded 0.8t/ha,” he says. “Roots in the spaded area reached a depth of more than 40cm, and the crop yielded 1.5t/ha.”
Tony was pleased with the results and was satisfied that the 0.7t/ha yield difference had covered the cost of liming and spading in the first year alone.
On 12 May 2013, Tony sent a message to his followers on the social media platform Twitter: “That beach sand (lime) does wonders to our soils. I can’t believe it took us so long to wake up.”
Tony says he uses social media as a way to start conversations with pioneers in spading and mouldboard ploughing who farm in regions beyond his immediate district; and to ask questions related to herbicide use and which crops are suited to recently spaded soil.
Last year, the yellow sand spaded in 2012 was planted to lupins and after discussions with another grower on Twitter and people at various grower group events, he decided to ‘go easy’ on residual herbicides so as not to damage the crop.
The lupins planted on the spaded soil yielded 2.6t/ha in 2013, a pleasing result for Tony because it was well up from their long-term 1.5t/ha average.
In 2013, Tony was keen to ameliorate more of his yellow sand using the spader, but this time he also wanted to test the impact of mouldboard ploughing.
He spread 2.5t/ha of lime for about $60/ha (including transport). Contractors were hired to incorporate the lime into the subsoil, with the spader arriving on 24 May and the mouldboard plough on 30 May.
Although the mouldboard plough ($120/ha) was slightly more expensive to hire than the spader ($110/ha), so far Tony says he is happier with the return on investment he has achieved with the mouldboard plough.
Without mouldboard ploughing, he estimates the paddock of wheat he ameliorated would have yielded 2t/ha. However, incorporating the lime enabled it to achieve 3.3t/ha – a 1.3t/ha increase.
According to Tony, two of the benefits of mouldboard ploughing are its superior burial of weed seeds and better capacity to handle gravel soils.
However, the downsides include a smaller window of opportunity for mouldboard ploughing compared with spading and that paddocks mouldboard ploughed in 2013 may need a further 2t/ha of lime added to the topsoil this year, depending on soil test results.
Mr Gazey encourages growers to carry out soil tests after mouldboard ploughing.
“Effective mouldboard ploughing to bury weed seeds inverts the soil, so it also brings acidic subsurface soil to the surface, which can potentially lead to crop failure,” he says.
Tony overcame this in 2013 by growing Wyalkatchem wheat and had no problems with crop establishment because of the variety’s tolerance of acid soils.
However, he says there were some establishment issues caused by compaction in the wheel tracks of his tow-behind airseeder. In these areas, the clay on the surface had crusted over because there was no rain for three weeks after sowing.
One of the paddocks Tony had earmarked for liming and spading in 2013 included a small patch of land that had been set aside for a fertiliser company to run long-term nutrition trials. Tony asked company representatives if they wanted the area limed and spaded, but they decided to leave it untreated.
The difference in crop growth between the treated and untreated areas attracted plenty of interest among growers at the MMPIG crop walk when those who had seen the trial shared photos they had taken.
By the end of October there was still a difference between the two areas. However, Tony says the final yields were not as high as they could have been because of an explosion of brome grass on the limed and spaded part of the paddock.
“The spaded country yielded 2.6t/ha on average, while the best of the fertiliser trials yielded 2t/ha,” he says. “To control the brome grass this year, we’ll grow a competitive crop of Scope barley and use an in-crop application of imidazolinone herbicide as part of the Clearfield production system.” Tony says he needs to keep a closer eye on subsoil acidity and weed management than he has in the past; and has a further 130ha left to treat with a spader or mouldboard plough.
Recently, as a member of the GRDC’s Kwinana West Regional Cropping Solutions Network, Tony voiced his support for a “go-to person” who growers can ring to discuss issues around liming, spading and mouldboard ploughing.
“I’d like to know the best crops and weed-control methods to use in the second and third years after lime incorporation to maintain our yields,” he says.
“We need to attract more research communicators into our sector to drive adoption, otherwise we risk reinventing the wheel every 20 years.”
0427 541 122,
0429 107 976,
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GRDC Project Code DAW00236, SDI00006, DAW00204, Caring for our Country Research Code SP11-01226