- Owner: Rod Kershaw
- Manager: Nick Kershaw
- Location: Greenethorpe, NSW
- Average annual rainfall: 500 to 600 millimetres
- Area cropped: 550 hectares
- Farm area: 1150ha
- Soil pH (calcium chloride): 4.2 to 6.0
- Soil type: clay loam over clay
- Crops grown: Coolah wheat (PBR), Kittyhawk wheat (PBR), RGT Planet barley (PBR), PBA HatTrick chickpeas (PBR), Hyola 970 canola
- Sheep enterprise: 3000 Merino ewes
A trial incorporating chickpeas on Nick and Rod Kershaw's mixed farm near Greenethorpe, New South Wales, alerted the father-and-son team to a yield-robbing subsurface acidity problem that was eating away at farm profits.
The four-year farming systems trial, which includes sites at Wagga Wagga, Urana and Condobolin, has GRDC, CSIRO and NSW Department of Primary Industries co-investment to examine the impact of different cropping sequences on water and nitrogen resources to determine the most profitable rotation over three years.
CSIRO Agriculture and Food senior experimental scientist Tony Swan says high-value and shallower-rooted chickpeas and lentils are some of the pulse crops being examined for their capacity to fit well with early sown grazing cereals and canola, due to the lower nitrogen and water requirement. However, they require a pH of more than 6.0 (calcium chloride) to thrive.
Soil analysis in 2017 of the Kershaws' paddock where the trial is located revealed a pH of 4.2 (calcium chloride), five to 15 centimetres beneath the soil surface.
Mr Swan says the pH was a significant subsoil constraint to root growth and legume nodulation. Below 15cm, the pH was about 5.0 (calcium chloride).
"We started observing this subsoil acidity from early 2011, as have many other researchers in southern NSW," Mr Swan says.
Nick and Rod had previously applied lime to the paddock where the trial is located and, like most farmers direct-drilling crops, had incorporated it by sowing alone using knife-points set on 250-millimetre spacings.
Mr Swan says that even with the Kershaws' method of sowing (sowing at 90 degrees in the opposite direction to the previous year, which results in better mixing of topsoil compared to inter-row sowing or with a disc seeder), the combination of applying industry rates of lime (2.5 tonnes/ha) and the inadequate incorporation from direct drilling was not sufficient to maintain the subsoil pH in the preferred range.
In March 2018, Mr Swan applied 3.5t/ha of lime and incorporated with a Speed Tiller, however the machine could only incorporate the ameliorant to a depth of 10 to 12cm.
Twelve months later, further soil tests showed the soil pH in the zero to 10cm layer was 5.7 to 6.0 (calcium chloride), but in the 10 to 15cm layer the pH was 4.5 (calcium chloride).
"We're suggesting to test pH in 5cm increments, apply enough lime to ameliorate the entire surface and subsurface soil, and incorporate it as deep as required depending on your soil tests," Mr Swan says.
"We understand the reluctance to cultivate in our mostly no-till systems, but untreated acidity will worsen over time and continue to rob yield and profit from the system."
Mr Swan says if a grower needs to incorporate lime to 15 to 20cm, the soil will need to be sufficiently wet to ensure maximum penetration by an offset disc or suitable implement.
"A good method may be to target paddocks with large stubble loads following a summer rainfall event and incorporate some fertiliser to assist breaking down the stubble," he says.
"If a paddock has low stubble cover, the grower might want to plant a crop quickly afterwards to reduce the risk of erosion. A paddock with less than 2t/ha of stubble residue would need to be sown to a crop to hold the topsoil together and minimise wind erosion and maximise water infiltration."
Going forward, Nick and Rod aim to test the soil to a depth of 30cm in 5cm increments to determine surface and subsurface lime needs.
The pair started growing PBA HatTrick (PBR) chickpeas for the first time in 2017, but admit that choosing the best sowing date and sowing rate have been two of the biggest challenges.
Last year, Nick and Rod sowed the chickpeas at 85 to 90kg/ha in late May, but the crop proved too thin, only yielding 0.9t/ha in a very dry (decile one) season.
Putting that crop down to experience, the pair this year sowed the chickpeas at 100kg/ha on 8 May.
When GroundCover™ spoke to Nick in late September, he said the chickpeas were a "clear standout" compared to other crops on the farm.
"They have potential to yield more with more rain, but at this stage I'm hoping for yields of 1.2 to 1.5t/ha," he says.
In March 2019, Nick and Rod applied lime to about 100 hectares of the farm at rates of up to 3.5t/ha. The product was again incorporated using their offset disc. Nick says February and March is the most practical time to incorporate lime.
This year is the Kershaw family's first foray back into barley after dropping it out of their cropping sequence several years ago.
The barley was planted on 14 May at 60kg/ha. At the end of September, Nick said the crop looked good. "Barley and chickpeas have been standouts in the dry and we plan to grow more barley next year," he says.
"Our agronomist Peter Watt worked out that if barley was grown on the farm during the past five years we would have pocketed 18 per cent more profit."
Nick says the farming systems trial, incorporating moisture probes in different treatments, was a decision-making lifesaver this year because he was able to ask Mr Swan how much soil moisture was available under various crops.
"Knowing how much moisture was under various crops was critical as rainfall became more limited from early September," he says.
"If we thought a wheat crop would run out of moisture because it was sown on to a canola paddock that was grazed last year, we decided to put stock on that paddock rather than take it through to grain," he says.
GRDC Research Codes CFF00011, CSP1904-005RXT