- Trial Rationale
- Steps Taken
- Lessons Learnt
- Looking Forward
Keyline Farming is a holistic approach partly aimed at capturing water on-farm and improving soil. Developed by PA Yeomans, the approach includes deep ripping at increasing depth to improve water infiltration and root penetration.
In 2015, Boyup Brook Farmers Veronica Nix and Darren King began a demonstration of Keyline ploughing on a sloping, annual pasture paddock. Their motivation was to limit runoff and erosion caused by summer and break-of-season rainfall and increase soil carbon and productivity.
“Our opening rains might be 20 mm in 20 minutes that can take out fences and create gully erosion. So we wanted to stop erosion by slowing water movement down the hillside,” Veronica said.
The demonstration paddock was deep-ripped in 2015 and again in 2016 at greater depth. Lime, dolomite and chicken manure (1.5 tonne / ha) was applied to soil described as a granitic loam with a dense subsoil, sodic soils in a gully, a pH of 6.2 (in H2O), low phosphorus (7 ppm—Olsen, PBI—187), and soil organic carbon of 3.7%. Soil tests were collected in 2014 and 2017.
Observations suggest that deep ripping was successful in reducing run-off.
“There was a lot of moisture being held at the top of the hills, whereas other paddocks seem to shed more water,” Veronica said.
But ploughing was time-consuming, tricky to time right, and had some negative outcomes.
“You need moisture in the soil to avoid damaging soil structure and the plough itself, but not too much moisture. It can be a small window.”
Follow-up rain can also be important. In 2015, Veronica ploughed in early spring. The lack of follow-up rain meant the disturbed grass died.
“The cattle also like to dig holes in it and make a mess, so it’s best if the paddock can be locked up.
“It’s a very slow process, a lot slower than I initially envisaged. We’ve got an 8-foot plough. Ideally you need something twice that size because it is such a slow pass.
“The concern we have is that the paddock is so rough from ploughing (a concern for hay or silage paddocks). If we had a roller behind it we could reduce this significantly, and it might limit the risk of grass dying. Ideally you want coulters on the front to cut through any grass and a roller on the back to lightly press down what’s there.”
There was no evidence of production benefits from ploughing, liming and chicken manure. Phosphorus remained well below desired levels of 17 ppm (Olsen) and was likely a key limitation.
It has been said that keyline ploughing can improve soil carbon, although this wasn’t supported by trials run by On Pasture. Monitoring in this demonstration was not sufficient to conclude any significant changes in soil carbon.
Increased plant production is important to increase soil carbon, but other constraints such as low phosphorus have likely limited any increase in plant production. This suggests that to get the full benefit of deep ripping or keyline ploughing, in terms of plant production and carbon sequestration, all soil constraints must be addressed.
Another principle of Keyline Farming is the use of perennial plants, which can also help to control summer and autumn run-off. Veronica and Darren planted carob trees on some rip-lines, but a dry spring in 2015 meant survival was low.
“Carob trees are not as hardy as thought and they are slow growing without reticulation.”
An alternative to carobs raised at the project’s first event in 2015 was the use of forage shrubs.
Veronica and Darren are also interested in perennial pastures like deep-rooted Lucerne, commonly used for managing groundwater with examples near Boyup Brook (link). However, Lucerne is often cut for hay, and responds well to being cut, so a smoother paddock is preferred.
Deep-ripping on contour can slow run-off and increase infiltration (though not guaranteed on water repellent soils), reducing the volume of run-off and sheet erosion risk (but may increase tunnel erosion risk on duplex soils). But rolling the surface may result in fewer obstacles to overland flow, resulting in increased flow velocity and reduced the opportunity for infiltration.
Flow velocity can also be reduced by groundcover, while healthy, deep root systems such as perennials can improve infiltration, use water and control run-off volumes and risk of tunnel erosion.
To get the most production, soil carbon and erosion control gain from deep ripping, growers should consider all soil limitations and consider using deep-rooted plants either in strips or across the whole paddock. Good groundcover management can retain erosion control if paddocks are rolled, and healthy root systems in fertile soils will reduce the rate of re-compaction. Liming prior to ripping to incorporate lime at depth will also address any subsoil acidity issues, which like compaction, can also limit root depth.
Veronica and Darren will continue trialling the practice.
“There is some interest in attaching a roller and coulters to the plough as well as set up some sort of soil amendment injection system (rip and drip carbon system),” Veronica said. “However, the cost is quite large.”
A similar project combining deep ripping with organic fertiliser also on duplex soils has been carried out in Tasmania, and is now part of a national GRDC project.