Most farm paddocks have a long history of phosphorus build-up that represents a lifetime of investment in soil fertility. With phosphorus and other nutrients concentrated at the soil surface, leaving soil bare and exposed to wind and water erosion is putting that investment at a significant risk, especially given that nutrients are commonly attached to finer clay soil particles which can be transported long distances by wind and waterflow.
The topic of how best to protect paddocks over summer and autumn was discussed at a recent “Grazing Matcher” group meeting in Donnybrook, which heard from local agronomist Dan Parnell.
“The risk of erosion is a big issue on hills when we bare-out areas that are then vulnerable to wind and rain. You can lose valuable topsoil down the hill in summer storms or harsh opening rains. So, you want to have enough of the soil covered with pasture residue to keep the soil in place.”
One tool to maintain cover on paddocks is rotational grazing. While this is more commonly associated with the management of living plants, it can also be useful in dry months.
“Most people still keep rotating over summer to try to keep control on the grazing and get an even residual (post grazing cover). The alternative of leaving stock in a paddock for a considerable time means they can be more selective and put too much pressure on specific areas. This leads to a combination of overgrazed bare areas and under-utilised areas that remain a fire hazard.
“With rotational grazing, it’s the farmer who is in control of the residuals, not the animals. So, they keep rotating until they reach a minimum groundcover target. The minimum target for groundcover suggested by Evergraze is 70% (or 800 kilograms of dry matter per hectare), but this should be closer to 100% on steeper paddocks.”
Another benefit of retaining cover on paddocks is the effect on seedling establishment. One farmer at the meeting spoke of how he had better establishment in 2019 where there was more groundcover, putting the result down to the groundcover acting as a mulch and conserving soil moisture after rain. Another possibility is that groundcover increases infiltration and reduces the effect of raindrop impact on bare soil. The power of a raindrop can smash aggregates apart, not only making them prone to transportation, but also blocking pores and creating a hardpan on the soil surface that can inhibit seedling emergence. Retaining groundcover reduces this risk and remains useful when green pasture starts growing by adding roughage into the diet.
However, it is hard to stay above minimum groundcover levels in all paddocks, especially if early-season grazing is deferred to allow pastures to establish. One or more paddocks are typically sacrificed and grazed below target levels to protect other paddocks. These sacrificial paddocks should be in an area protected from wind and runoff such as a flat, timbered area where the risk and impact of erosion is lowest. Paddocks that need renovating are often sacrificed so stock can control weeds and the impact of heavy grazing is overcome by re-seeding.
Farmers can take steps towards protecting paddocks now by setting groundcover targets, selecting sacrifice paddocks and considering feed budgets early in the dry season.
For those looking for more assistance with grazing and feed management, the Grazing Matcher Program is due to start a new group in March 2020. For more information contact Peter Clifton, Regional Agriculture, Landcare Facilitator, at the South West Catchments Council on (08) 9724 2469.
This project is supported by the South West Catchments Council, though funding from the Australian Government’s National Landcare Program, and Western Beef Association Inc.