Deciding when to irrigate should not be based on what the neighbour’s doing, Tony Davoren says.
The founder and managing director of HydroServices Ltd spoke at an irrigation efficiency field day near Waimate late last week. Wainono Community Catchment Group in conjunction with the Morven Glenavy Ikawai Irrigation Company at Dave Ellis’ farm at Waihao Forks.
Dr Davoren told about 80 attendees he was appalled to see many irrigators working on the Canterbury Plains as he travelled to the field day.
He cautioned farmers against “making decisions on gut feelings or perceptions or what the neighbour’s doing”.
“Soil temperatures are not high enough yet. It’s not water inhibiting growth now. It’s soil temperature and day length.”
The only sensible way to decide when to start irrigating was by using information from below the ground.
“Nothing beats digging a hole. See what the soil looks like.”
He demonstrated in small a trench dug on the farm, showing the different strata. The dark section at the top, the A horizon, contained all organic matter and the bottom section, the C horizon, contained gravels.
Pasture was a shallow-rooted crop that reached only about 30cm into the soil. Lucerne roots, though, could go down further than a metre.
“You’ve got to manage your soil moisture over these depths.”
The thickness of the A horizon was the key, he said. In the trench, it was 20cm.
“All the action takes place in the top 20cm. That’s where the nutrients are stored. Anything beyond goes to drainage.
“Dig more than one hole – see what you’ve got.”
He recommended taking one reading below the A horizon, to show what was draining out of the soil profile. Farmers could see if they were irrigating too soon, putting on too much water, or causing nutrients to leach out.
measurements down through the soil profile. You can see where the roots are, if there are soil problems, if there is compaction that needs attention, if water is draining from one part of the profile to another.
“You need to record the measurements,” he said.
A telemetered system would take care of that, but if farmers were taking their own measurements they must be “methodical”, Dr Davoren said.
“Make sure you measure volumetrically if you buy a sensor. Soil moisture black boxes everything that happens underneath this crop. You can see how much water is being transpired. If you do it right, you can quantify drainage.
“You will have to run an Overseer model and establish long-term drainage from your property. You can quantify where the root zone is.”
Dr Davoren outlined the sensor options available – dielectric versions, neutron probes and capacitance sensors.
Whatever sensors were used, farmers still needed good information on the amount of water falling on their paddocks as irrigation or rainfall, he said.
Farmers should “invest in a $50 rain gauge and read it every day and measure your soil moisture – you’ll be 90% there”.