ABOVE-AVERAGE winter rain across large parts of southern grazing country, and forecasts for that to continue into spring, has raised questions about the risks of putting livestock on waterlogged or pugged soils.
Pasture experts say the costs in terms of reduced pasture yields and re-sowing are well-documented but the below-ground costs of damaging soil structure can be just as significant.
Animal health issues such as lameness, mastitis and magnesium deficiencies also need to be factored in when determining management strategies.
Sustainable agriculture officer with the Murray Local Land Services Sue Briggs, based in Albury, said livestock producers with low lying areas and heavy clay soils were reporting much higher subsoil moisture than typical for this time of year.
As soil gets wetter, it becomes weaker and compaction from grazing stock becomes an issue.
Pugging happens when the soil reaches saturation point, Ms Briggs said.
Pasture utilisation can be reduced by as much as 30 to 40 per cent and yields decreased by up to 80 per cent well into spring, Ms Briggs said.
That decreased production also opens paddocks up to a higher weed burden.
The hidden cost of soil structural decline was more difficult to measure, she said.
“Grazing waterlogged country results in pugging which reduces the size of pores that drain the soil, which means they waterlog quicker in the future,” Ms Briggs said.
“Prolonged waterlogging means those soils will remain colder for longer and take more time to respond to spring conditions.
“The anaerobic conditions also lead to a decline of favourable biological microbes that help with restoring soil structure.”
Most producers are familiar with the paddocks that are prone to waterlogging and pugging so the aim should be to have them grazed beforehand, she said.
“Where you don’t have the choice, aim to build up pasture cover to at least 2500 kilograms of dry matter per hectare to cushion the effect.”
The most effective strategy during periods of above-average rain for most farms, depending on infrastructure, is on-off grazing, according to Dairy Australia project development manager land, water and carbon Sam Oakden.
Dairy Australia’s Managing Wet Soils fact sheet, released this season, advises grazing cows for a limited time, usually two to four hours, and then moving to a standoff area - a ‘sacrifice paddock’.
Cows will usually consume 70 per cent of their daytime pasture intake in the first two hours of grazing and then up to 88pc by four hours, with the bulk of the pugging damage caused after that as they wander about.
Other strategies include supplementing, as well-fed cows do less walking around the paddock, and allocating a third of pasture for scheduled night feeds when cows rest more.
