Goulburn Valley dairy farmers are being warned that irrigating too often could result in a 20 per cent reduction in pasture growth, according to a recent study.
A study, directed by Goulburn-Murray Water and carried out by the University of Southern Queensland’s National Centre for Engineering, observed water application efficiency by looking at one irrigated bay on nine different Goulburn Valley farms in the 2013-14 season.
“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,” research team leader Professor Rod Smith said.
Farmers who participated in the study used Rubicon Water’s FarmConnect automated watering system and soil probes which store all data online and continuously measures soil moisture down to one-metre depths.
Dairy farmer Russell Pell lives on a property in Wyuna with his wife Cath and son Michael, growing an annual pasture as well as maize and wheat crops.
Mr Pell participated in the study and was also one of the first farmers in the Goulburn Valley to use the Rubicon system about four years ago.
Mr Pell said the moisture metres had been ‘invaluable’ and prior to the technology, decisions about when to irrigate were based on looking at the pasture or crops.
“I was giving it more water than I needed to,” Mr Pell said.
“We (farmers) probably didn’t know we were doing as much damage as what we did.”
During the study, when his “gut feeling” was that the maize crops needed water, Mr Pell said the moisture metre revealed there was still at least 30 per cent of moisture left to absorb.
Timing is essential in irrigation management and Mr Pell said the general rule was to have the plot (no bigger than 2ha) watered in under two hours to avoid a surplus of surface water and consequent waterlogging.
“Once you get beyond two hours you get deterioration in crop,” he said.
“Watering is a two prong thing: you need to know when to water and you need to water quickly.”
Mr Pell said farmers growing maize were getting on board with the technology quickly.
“Why wouldn’t you?… It’s inexpensive for what you get out of it and with the price of water nudging up towards $300/Ml, you need to grow a lot of tonnes per Ml to justify the price,” he said.
Mr Pell said faster irrigation resulted in more crops and a drier pasture and since using the moisture metres, he had produced a larger quantity and higher quality of maize at a more efficient rate.
“We were growing about 16-17 tonnes/ha of maize and now it’s up 25 tonnes… and that’s even with a little less water too,” he said.
Mr Pell also said because the moisture metres were read through an online system, farmers could take the data anywhere and enjoy greater flexibility.
“If you go away, you can take it with you and project where and when you need to water, otherwise you have to be at home to look at it and there is some guess work involved,” he said.
Prof Smith said the results of the study called into question the common belief that pastures are shallow-rooted and must be irrigated frequently.
Irrigating too often leads to waterlogging of soil and drainage run-off which causes a halt in pasture growth for days.
Prof Smith said the potential 20 per cent loss in production was due to over-saturating pastures and while many Goulburn Valley dairy farms have installed on-farm automation systems, more farmers needed to understand that less irrigating and the correct amount of water would produce best results.
“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 means you end up with a much drier profile on average,” he said.
The results showed irrigation application efficiencies greater than 90 per cent were achieved through precise management of automated irrigation.
“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.
“Another saw his crops wilting during that same hot period and irrigated again after only four days, so he super-imposed waterlogging on top of heat stress.”
The strongest performing participant was achieving 12 days of growth and eight or nine days available for grazing out of every 12-day watering period, Prof Smith said.
Mr Pell said the new system would not be able to function under the old G-MW distribution system, due to the flows being too inconsistent, and the modernisation of technology had been vital to growth production.
“The G-MW distribution system couldn’t supply water for the new technology – they had to get the system upgraded before we could do our stuff and it’s given us some really good opportunities,” he said.
“We need all the technology we can get in Australia because we are expensive country to do business… We have to be smart about how we do things.”