Author: Nicole Baxter
Grain Research & Development Corporation
Southern NSW grower David Wolfenden shares some of the lessons learned on his decades-long journey to tie improved soil health to income health.
Mixed farmer David Wolfenden says on-farm trials and his own observations have consistently shown that profitable returns are closely tied to the wellbeing of his land.
David, who farms at Rand in southern NSW, became interested in soil health in 1978 when he hosted a New South Wales Department of Primary Industries (DPI) trial investigating minimum tillage.
He could see the potential for improved soil health so he bought a one-pass seeder and became a founding member of the Southern Farm Management Group, a group of growers interested in trying new farm practices.
Soon after the group was formed the members looked into a system that had benefited irrigated growers.
The system, called Crop Check, encouraged soil and crop-health monitoring to improve returns.
Developed by former NSW DPI agronomist John Lacy, it suggested more than 10 checks were necessary to grow high-yielding wheat.
It was not long before David had implemented a dryland version of the system and was well on the way to improving yields.
“A key lesson was that good yields are a result of getting many factors right, with soil health a major contributor to most of these factors,” David says.
He points out that adopting minimum tillage followed by stubble retention started as an “act of faith” and took a decade to produce measurable benefits – the key indicator being improved profit.
As a consequence, David sees exploiting the benefits of improved soil biology as a long-term pursuit.
“We are only now starting to understand soil biology, and science is offering us the opportunity to open Pandora’s box,” he says.
“This research needs to continue if we want to fully harness the benefits of soil biology and increase our wheat yields to 10 tonnes per hectare.”
David’s next step was examining if in-paddock variation of water-holding capacity (WHC) was limiting yield. Electromagnetic surveys were completed and zones mapped.
In 2011, a trial investigated whether targeting nutrients to soil WHC could improve crop returns.
At sowing, monoammonium phosphate was applied across three zones at 5, 10 and 20 kilograms/ha of phosphorus.
Nitrogen was applied at 40kg/ha as urea during early August. The crop’s response was judged visually and at harvest by yield map, and compared with a nil-phosphorus plot.
The results showed a yield response up to 10kg/ha of phosphorus, even though soil tests indicated there was a high level of Colwell phosphorus (38 to 61 milligrams/kg) across the zones.
A gross margin analysis showed the added net income from applying 10kg/ha of phosphorus was $37/ha, resulting in a $2.63 return for every $1 spent.
There was no response to added nitrogen, possibly due to the dry spring and the time of application.
Feeding the bugs
Recently, David attended a workshop where CSIRO’s Dr Clive Kirkby discussed the importance of ‘feeding the bugs’ in the soil as a way of increasing crop growth.
His work suggests some freely available sulfur, phosphorus and nitrogen are required for the soil biology to maximise activity and break down stubble into plant-available nutrients.
Over the years, David says soil tests have shown an improvement in most nutrients including phosphorus, sulfur, calcium and magnesium.
Adding lime has lifted soil pH and reduced aluminium toxicity, allowing crops to thrive.
Going forward, he sees the challenges as refining practices across the zones and fully using soil biology activity.
With organic carbon (OC) at 1.8 per cent, he wonders if his farm management will need to change as it moves beyond two per cent.
“On top of minimum tillage and stubble retention, Dr Kirkby’s work may point to ways we can increase the biological activity and further increase OC levels,” David says.
“Studies indicate that yields might plateau when my OC levels reach two per cent, but
I believe research needs to look at whether we need to change our practices to utilise higher levels and maximise the potential of soil biology.”