Keith grower probes for better irrigation timing

Mr Cook, who farms at Keith, was a guest speaker at the Society of Precision Agriculture Australia conference held last month in Tas, discussing prescription irrigation in his sandy soils, with his travel funded by the SA Grains Industry Trust.

He has four Sentek probes on 175 hectares of irrigated lucerne stands, two probes on flood irrigation and two others under centre pivots.

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Each probe is constantly recording moisture levels at 10 centimetre increments from 10cm below the soil surface down to 80cm.

This information is logged every couple of hours and can be accessed remotely on the phone or computer to calculate the optimal time for watering seed crops throughout the spring-summer period.

"Lucerne is a crop that needs a declining soil moisture profile to trigger set seed so managing it to know how hard you can push it before the plant goes into shut down and flower drop is a big part of it," he said.

"For us it is not like we have doubled our yields and gone from one tonne a hectare to 2t/ha, but we are more consistently hitting the higher average with less variability from season to season (using the probes)."

Irrigation makes up about half of the area Mr Cook has dedicated to lucerne, growing three varieties for three seed companies as well as public varieties.

They also have a broadacre cropping program of wheat, lentils, canola, barley and oaten hay and a 1450-head Merino ewe flock mated to Poll Dorsets for prime lamb production.

Mr Cook stressed expert advice had been critical to good decision-making concerning irrigation timing, using The Alpha Group consulting to manage their data and assist in crop monitoring.

"Don't go it alone, you need someone from outside who can objectively look at the data and help with calibrating it and they are also out and about ground truthing it in-crop a couple of times a week," he said.

"They have 10 plus years of our data stored in their system and work with many others so know how far crops can be pushed on different soil types"

Mr Cook says soil moisture probes have come a long way from the neutron probes they first used a couple of decades ago and says remote transmitters that can be located on a check bank or edge of paddock have made it easier, rather than having to drive around the probes.

UNLIKE the United States, which has access to leaf cutter bees to enhance pollination, Keith lucerne seed grower Joe Cook says moisture probes are the main tool Australian growers have to manipulate flower drop and seed set.

"The longer you can keep a flowering crop in a declining soil moisture profile, the faster you can get a crop to seed set and the shorter the crop (time length) the higher the potential yield, but you need to make sure your system can handle it and you don't go too far beyond the refill point during the season," he said.

Mr Cook says EM38 mapping their irrigated paddocks in recent years to map soil types has further enhanced the accuracy of their irrigation scheduling, ensuring the probes are put in the most representative part of the paddock.

"The probes tell you ahead of time what you see a few days later on the surface - for us, not using probes would be like trying to cook a cake without a temperature gauge on an oven."

Lucerne Australia, with funding from AgriFutures Australia, is in the second year of a trial in the area looking at the yield response of 29 commercial and pre-release lucerne varieties under modified irrigation management.

In the first year of the trial, the high and moderate stress watering strategies produced up to 14 per cent higher yields than standard watering.

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