The couple operate a 435 hectare effective dairy operation on the south bank of the Waitaki River at Duntroon, in the Environment Canterbury catchment.
Geoff Keeling is more aware than most about the need for irrigation efficiency, and the growing link between irrigation application rates and nutrient losses.
He has participated in the zonal committee process as a Waitaki Council representative on the Lower Waitaki South Coastal Canterbury Zone committee. He was also a director and chairman of the Kurow-Duntroon Irrigation Company for the past six years and a director of both the Maerewhenua District Water Resource Company and the Waitaki Irrigators Collective.
“As the regulations have developed around water and nutrient losses, we wanted a system that would future-proof us against what was coming.”
The Keeling systems were designed and engineered by Kirk Irrigation at Waimate and Geoff Keeling attributed much of the system’s success to a focus on simplicity and logic.
The audit of Keeling’s Duntroon property in Otago examined two of the property’s three main systems.
Another system operates three pivots covering 95ha, 40ha of K-line and 6ha fixed grid. Water is pumped from a dam with pump at the high point of the system and a 50kW pump operating on a Variable Speed Drive (VSD). Due to electrical issues on the day this couldn’t be tested.
The twin pivot/K-line combination identified as Takiroa covers 91ha, and the K-line only system, SH83, covers 70ha of the farm.
“The system is based on it being easier to pump water downhill rather than uphill and Rob Kirk has not overcomplicated things, based from that.”
They established the systems as they have converted from border-dyke to spray systems over the past two to five years.
When they developed the Takiroa system, one option presented to them by another company was to put a large single pivot irrigator in place.
“While it may have been good for egos, it was not ideal. The practicality of having one big pivot close to the river where we had lost two hectares left us exposed.”
Instead the twin pivot system spreads the risk, and both pivots are capable of operating at the same time at just under the consented flow rate of 40 litres a second.
The SH83 system using the K-line irrigators sources water from the Kurow-Duntroon Irrigation Company, with company water stored in two dams situated higher on the property.
“After pumping water into them, we wanted to minimise pumping out of them, and with the dams we had positive head pressure for the pumps.”
A combination of factors in addition to good design have also helped the system be more efficient than most.
The property’s system’s success is founded on the right sizing of pumps and having VSD technology on delivery pumps that keep the operating point of the pump close to its efficient optimum.
This ensures a substantial reduction in power accompanying any reduction in flow and ensures pumps hit the “sweet spot” of maximum efficiency where flow rate maximises that point.
The audit found the Takiroa pump sized up at 45l flow rate operated close to its BEP (Best Efficiency Point).
The SH83 system also has a VSD in place, with pumping flow rate never exceeding 30l a second, and despite the considerable variation in flow rate it still resulted in a BEP of 81%.
NZ Irrigation Design Standards recommend a velocity flow rate no more than 3 metres/second, and the audit revealed a maximum flow rate of 1.5m/s, and no more than 2.3m/s.
The SH83 system had a flow velocity of 1.7m/s.
The property also had an efficient mainline delivery system. Irrigation standards require losses in the mainline be limited to between 1.5 and 5m/100m, and a flow velocity of no more than 2m/s.
Geoff Keeling said there was also an element of good fortune that helped ensure the farm’s system operated efficiently.
Being close to the river and using surface source for one system and dam supply for the other meant pump delivery was relatively straightforward.
“The further you get from your source you have to move away from a single pumping system, and it can get complicated and expensive quickly.”
Efficiencies in Keeling system
He acknowledges the costs of VSD technology, at about $15,000 a pump, have bought real savings, but says the benefits are only worth it if the pump is delivering across a decent area.
“I have another system with an 18kW pump covering 40ha, but the $15,000 cost of a VSD, it’s just not worth it.”
Increasingly irrigators using VSDs are also facing the additional expense of filtering equipment to suppress “harmonic distortion”, the electrical signals that affect electricity quality in transmission. This can amount to an additional $10,000-$15,000 a pump.
The Duntroon property is also blessed with relatively heavy soils, with a Plant Available Water capacity of 300mm on the Otiake sandy loam.
This provides the system with an allowable application rate of 4mm a day on the Takiroa centre pivot system over 150 days against 5mm over 120 days.
The heavier soils also mean the farm sits comfortably in the Green Zone’s allowable nutrient losses, at about 22kg nitrogen/ha/year, compared with almost double that under a flood border-dyke system.
“And that loss could be double that on lighter stony soils on the Plains.”
