As we enter the final month of winter, the price our productive soils pay for being left unprotected during periods of heavy rainfall are again becoming evident.
During the wetter months, there are extended periods where soil is left bare during fallow periods and crop establishment, presenting a high risk of soil erosion. Rills are visible in paddocks with little or no ground cover where downhill water movement has stripped soil away creating channels. Soil washed onto rural roads can create a hazard for drivers, and huge plumes of soil entering Bass Strait from the northern rivers are striking features of aerial imagery.
The average rate of soil erosion across Australia is 1.86 tonnes per hectare each year, but this figure can be much higher from just one rainfall event alone in Tasmania. How can we keep our soil healthy and maintain long term farm productivity if we don’t keep it in our paddocks? Indeed, the soils of the Cradle Coast are highly productive – our region accounts for around 40% of Tasmania’s agricultural productivity from only 19% of the state’s of farmland.
The 10-20 cm of topsoil is where much of the soil/plant interaction occurs, and under our temperate climatic conditions, can take thousands of years to form.
No farmer wants to lose their soil, but with consumers demanding a range of cool climate vegetables to be available throughout the year, coupled with our temperate climate and soils suitable for cropping, some level of bare ground during autumn and winter is largely inevitable. There are however ways we can reduce the risk and severity of soil erosion in cropping paddocks.
Within sloping paddocks, rip lines or mulched rip lines installed along paddock contours act as a sponge, trapping soil washed down from further up the slope. This at least keeps the soil within the paddock, as the water itself enters the soil profile through the rip line, preventing surface water runoff building up greater velocity and continuing downhill to erode more soil. The faster water moves downhill, the more soil it can take with it.
Including a green manure or cover crop phase in a crop rotation could be an option for keeping steeper cropping ground protected during the wetter months. Any plant material, be it living plants or dead crop stubble, will slow water movement down the slope and reduce the risk and severity of erosion.
Cradle Coast NRM is launching a sustainable agriculture project with a focus on reducing the effects of hillslope erosion. To register you interest please contact Cradle Coast NRM Regional Agriculture Landcare Facilitator Tom O’Malley via email at tomalley@cradlecoast.com