Irrigation timing key in pasture trial


QUANTIFYING dairy pasture yield improvement through better water scheduling is one of the aims of a national Smarter Irrigation Project (SIP) participation at Dardanup.

Dairy farmer Michael Twomey, who was involved with the first phase of the SIP on an irrigated portion of his farm last year and into this year over summer, is preparing to participate in phase two – or SIP2 as it is known – from next month.

Mr Twomey and Western Dairy hosted an information session and pasture walk recently, attended by about 20 dairy farmers and fertiliser and irrigation equipment providers, to explain SIP2’s aims and objectives.

The project was triggered by farm trials in Tasmania which indicated a doubling of production over three years was possible using the same or slightly less water, but with smarter application, particularly in relation to timing of seasonal irrigation start up and watering volumes and frequencies.

As a national project, it also covers the cotton, sugar, rice and grains industries, as well as dairy.

SIP2 is trying to establish matrixes for each industry that will help narrow the ‘yield gap’ – the difference between actual and potential readily available water (RAW) efficiency.

RAW is the amount of soil moisture accessible to plant roots and its volume is determined by soil texture and plant root depth.

Maintaining optimum RAW is achieving a balance between rainfall and irrigation inputs and evaporation and plant transpiration losses at a required level.

The national project is funded by the Federal Department of Agriculture, Water and the Environment, with the dairy research component supported by Dairy Australia.

Dr Peter Hutton, who previously worked for Western Dairy but on SIP2 is working for Dairy Australia, will be co-ordinating the collection, interpretation and dissemination of data from three soil moisture probes at a 12-hectare sandy loam site on Mr Twomey’s farm.

He is proposing to post weekly data updates from the probes, along with rising-plate pasture growth measurements online.

Dr Hutton is also responsible for a similar role at a site in central New South Wales – there are 10 dairy sites around Australia involved in SIP2, but Mr Twomey’s farm is the only site in WA.

“There’s the idea dairy is a little behind (other branches of agriculture) in irrigation (efficiency),” Dr Hutton told the information session last week.

“We can take a lot of knowledge out of those other areas to benefit dairy.

“Once we know what the readily available water is, then it’s all about irrigation scheduling so we get the right amount of water on at the right time.”

Apart from studying what it takes to maintain RAW through delivery volumes and frequencies, SIP2 will also look at the cost of “narrowing the yield gap” by avoiding “green drought”, Dr Hutton said.

Green drought is when plant growth is inhibited by lack of moisture but there is just enough for the plant to remain green, disguising the fact it is stressed.

Dr Hutton pointed out once RAW dropped below a calculable “refill point”, it was extremely difficult to get it back by irrigation alone to a level where it was not impeding growth.

Mr Twomey explained almost 100 hectares of his farm’s 220ha dairy platform could be irrigated via four centre-pivots – two 34ha, a 16ha and a 12ha – fed by three 75 kiloWatt pumps on a dam.

The pumps were sufficiently powerful to run three of the centre pivots at the same time if needed, he said.

The system was purchased as a package from Thinkwater Bunbury, installed in 2015-16, geared to go around in a 10-hour period, delivering nine-10 millilitres and set up to use off-peak electricity between 10pm and 8am weekdays and at weekends.

Over summer Mr Twomey usually irrigates four nights a week to minimise evaporation loss – it can be more than half his delivery rate on a summer’s day – and take advantage of lower power costs.

The SIP2 site, which is almost half the coverage area of one of the large centre pivots, was currently sown with chicory – described by Mr Twomey as a “godsend in summer” – and annual ryegrass.

“I’ll cut that for silage so everything is nice and even and then I’m going to sow biannual ryegrass into it – we look like we’ll do that in the first week of October,” Mr Twomey said.

“I’ll get biannual in there and watered early October so it all gets off to a good start, I’m not doing it mid November when it’s a bit dry,” he said.

“Whereas millet (sown for several previous years on the farm) can handle the heat, the biannual doesn’t handle it nearly as well.

“It’ll be grazed as part of the normal rotation.”

Mr Twomey said his 380-400 crossbred cows would be on a 21-day summer paddock rotation, feeding on pasture at night, on silage during the day and currently getting five kilograms of grain in the dairy – but he is looking to reduce the grain amount by half a kilogram at a time down to 4kg as milk production declines into summer.

“My cows are over their 100-day (milk production) peak so I have to accept a lower milk volume, although I don’t want to,” he said.

“All we’re doing (with SIP2) is monitoring the soil probes and all the info that Peter is going to feed to us will control how much water we need to put on there to try to get the grass growing at its optimum due to the amount of readily available water we have,” Mr Twomey said.

Valuable lessons from being involved in SIP can be built on with SIP2.

“Last year was an information gathering exercise and the main thing to come out of it was that I basically started watering too late, even though it looked green,” he said.

“The readily available water had already been lost and I’m very tight with water – I hate overwatering – so I wasn’t watering enough.

“I got saved in late January by a shower of rain, because my growth rates were going down.

“But that shower filled up (RAW in the soil profile) and we were able to maintain it from there.

“(This time) with the trial pivot running independently, I’m dropping 8-9mm on the site.

“I do that four times a week.

“I want to see if I put 16mm on twice a week, am I using that water better or will I get run off?”

Mr Twomey pointed out that to avoid setbacks to his pasture feed and silage programs, he had his centre pivots professionally serviced each year prior to irrigating season.

Apart from obvious things like checking for blocked nozzles and leaks which could cause a drop in water pressure, it also covered less obvious aspects like pressures in tyres which could prevent the pivot travelling full distance, he said.

As part of the pasture walk and information session, Western Dairy agronomist Dan Parnell also discussed the farm’s silage program with Mr Twomey and how he determined which paddocks to drop out of rotation to lock up for silage.

About 120ha of the farm is cut for pasture silage each spring.

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