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Studies show overwatering cuts dairy pasture growth by up to 20 percent

Cattle in a paddock. Irrigation equipment overhead. Ute at right.
USQ studies have indicated overwatering could be costing dairy farmers up to 20 percent in lost pasture production (image credit - Dairy Australia).
Studies by a team from the University of Southern Queensland (USQ) have shown that overwatering of pastures could be costing Goulburn Valley dairy farmers up to 20 percent in lost production.

“If dairy farmers are irrigating 15 times in a season, and each time they lose two days pasture growth due to waterlogging, there’s 30 days out of a 150-day season gone. That’s pretty crucial — 20 percent in a season,” research team leader Professor Rod Smith said.

His data has come from studies commissioned by Goulburn-Murray Water and carried out by USQ’s National Centre for Engineering (NCEA).

Professor Smith said the results challenge longstanding watering traditions, including the belief that pastures are shallow-rooted and must be irrigated frequently.

“You don’t have to irrigate every seven days; you can stretch it out to 10 or 12 days and pastures will respond by putting roots down deeper, which mean you end up with a much drier profile on average.”

The most recent NCEA study looked at water application efficiency by examining one irrigated bay on each of nine different Goulburn Valley farms in the 2013-14 season.

Participating farmers had installed the Rubicon FarmConnectTM automated watering system, along with soil moisture probes which continuously measure soil moisture down to one metre, with all data collected automatically and stored online.

Results showed irrigation application efficiencies in excess of 90 percent were achieved through precise management of automated irrigation in four of the bays; for the other five, strategies were identified that could raise their efficiency to a similar level.

“What we’ve seen is farmers irrigating too often, and soils becoming waterlogged, with drainage running off and pasture stopping growing for days on end,” Professor Smith said.

“If you irrigate every seven days, for the first two days, the plants are not growing and the pasture can’t be grazed, and you can’t put cows on for the last two days, so you have opportunities for grazing for only three days.

“The consequence is 20 percent in potential production is lost by pastures being too wet, and the message we want to get out is irrigate less often, put on the right amount of water, and have much more productive pastures.”

Professor Smith said a “sea change” was required in the dairy industry to encourage investment and trust in precision irrigation systems, because they have been shown to be more effective than personal schedules like once-a-week watering, or visual prompts.

“We had a very hot February 2014, and pastures were wilting. One grower looked at his soil moisture graph on his computer and saw there was adequate soil moisture, so he didn’t water and his pastures took off when the days got cooler,” he said.

“Another saw his crops wilting during that same hot period and irrigated again after only four days , so he superimposed waterlogging on top of heat stress.”

Professor Smith said the top performer in the group was getting 12 days of growth and eight or nine days available for grazing out of every 12-day watering period as well as achieving application efficiencies of in excess of 90 percent.

“This farm applied very consistent management, and started each irrigation at about the same soil moisture deficit of 90mm, and over constant irrigation durations of 90 minutes that minimised tail-water run-off.”

Professor Smith said irrigators using non-precision systems typically applied 30pc more water than was needed to replenish soil-moisture deficits, and therefore risked nutrient loss and deep percolation.

“Those who don’t use moisture monitors also get erratic behaviour of crops, and soil damage,” he said.

While many Goulburn Valley dairy farms have installed on-farm automation systems, as well as adopting the recommended higher flow rates, Professor Smith said he believed Dairy Australia should be funding more research and extension to encourage producers to water faster and less frequently over shorter periods.

“We’ve been pushing that message for a number of years – faster flow over less time to at least 0.2 megalitres per day per metre,” he said.

Studies in 2009 and 2010 showed average irrigation application efficiencies on bay-irrigated dairy farms in the Goulburn Murray Irrigation District to be at about 69pc, and Professor Smith said the fact that this latest study has shown automated systems can hit 90pc is something the dairy industry should be shouting from the rooftops.

Professor Smith said promoting the productivity and sustainability gains to be made through precision irrigation was a better investment than researching ways of combating the effects of overwatering by removing excess water from pastures.