Friday, March 29, 2024

No labour and more grass

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Shifting 260ha of K-line for four months every year was like a life sentence for the Sowman brothers in Golden Bay.
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Pivots were out of the question with hundreds of mature totara trees so they installed a fixed grid system with radio-controlled solenoid valves on 130ha that requires no labour and grows more grass.

Corrigan Sowman and his brother Sam manage the family farm that spreads over 330ha of picturesque valley floor at Upper Takaka. Totaras which covered the valley when it was settled back in the 1890s are regarded by Corrigan as part of their heritage as well as part of the farm. They're the third Sowman generation on the property that has expanded from 80ha to today's 330ha in the past 25 years under the direction of their parents Brian and Glenda, with a 270ha milking platform.

The family started out with K-line irrigation about 13 years ago in response to the classic Golden Bay dry spell. Initially the goal was simply to keep the farm green until it rained again. Typical of most farms in the area, the annual rainfall is measured in metres and in the Sowman's case adds up to about 2.1m, but it's unevenly spread and they can go from torrential rain to drought.

Corrigan returned to the farm six years ago after working as a Dexcel (now DairyNZ) and FarmRight consultant and he's now the South Island Dairy Event chairman. His wife Ruth Guthrie has an academic background in ecology and their zeal for data put irrigation under scrutiny.

That led to speeding the system up to lift grass growth and also expanding the area until they reached 260ha K-line on a 10-day return, which produced more grass but meant they were spending five hours a day shifting it. That included 30ha on the 130ha runoff at nearby East Takaka to assist young stock through the dry and silage production.

Apart from labour, repairs and maintenance were increasing on the ageing K-line and its efficiency depended upon the skill of the team to shift it. A huge number of hours were spent on quad bikes and Corrigan said they wanted to use their staff time and their own time more constructively.

"We were getting progressive lifts out of tinkering with water and pushing towards 16 tonnes drymatter (DM). But it's almost a life sentence when you know every summer you have 260ha of K-line to shift for four months," Corrigan said.

They'd already simplified life on the farm and cut labour hours three years earlier when they replaced two herringbone dairies on the farm with a 54-bail rotary and Milfos Intelscan Plus technology, so it was time to simplify the irrigation system.

It's a long, narrow property that, combined with the totara trees, meant it wasn't conducive to pivot irrigation, but Corrigan had been watching the progress of the fixed grid system on a Rakaia Island dairy farm in Canterbury and reckoned it could work on their farm. So with payouts looking good, they took the plunge.

It was no small feat converting their K-line system to fixed grid and it took 12 months to first dig up the PVC for the K-line – which would have been simple enough if the stock water line was not in the same trench – and then replace it with a PVC ring line around the farm that is linked to 29 zones that each have between 75 and 85 sprinklers. All up, the fixed-grid system has 50km of 50mm LD pipe leading to sprinklers on 2300 posts.

“Any way you look at it, it's a complicated system to put in and a lot of manpower.”

The sprinkler location was set with GPS and the pipes laid using a mole plough with a slot to allow the pipe to flow through. Tapping saddles and 20mm risers were fitted to the pipe before it passed through the mole plough, so there was no need to dig in each sprinkler. Posts were driven in beside the risers and 20mm pipe clipped to the post and post riser on top, with the sprinkler fitted after the system was thoroughly flushed.

Radio-controlled solenoid valves were the finishing touch which means there's no labour required to manage the irrigation on that part of the farm. A message can bounce between the various antennae to reach the right one. Even when the hydro scheme further up the Takaka River prompts irrigation to cease, a message is relayed to the radio antennae to pause.

Each zone uses between 25 and 30 litres a second at 2.6mm an hour – 100,000 litres an hour, with pumps running off variable speed drive to regulate pressure and flow to different-sized zones as well as being more efficient with power.

Sprinklers are set up to irrigate every 3.2 days, delivering 15ml with every pass, with the opportunity to alter that simply by radio from 5mm to 25mm.

“That was a prerequisite because it had to have no labour.”

With the K-line delivering 45mm on each pass, Corrigan estimates about 20mm is wasted below the root zone, whereas the fixed-grid sprinklers can be easily altered to achieve enough water in the root zone. Posts in the fixed-grid system are offset so that the sprinklers' circles overlap each other and the distribution uniformity is between 70% and 80% compared with the K-line that was between 30% and 40%.

Corrigan expects the fixed-grid system to grow as much grass as a pivot and though the paddocks look a mass of posts, they haven't proved a problem with crops and mowing. This season they have mown the farm twice because they were shifting K-line less and had more time to sit on the tractor and Corrigan said the mowing gave them a noticeable lift in grass quality and metabolisable energy.

The cows were eating more pasture as well through summer – about 13.9t DM/ha compared with 11t in the past. Their goal is to lift that to 16t but though they now have a "Ferrari-style irrigation system", they have "HQ Holden grass underneath" that needs addressing to achieve it.

"We want to drive down stocking rate and drive up production efficiency and have less reliance on bought-in feed and more quality grass."

In the past few years they have averaged 3.1 to 3.4 cows/ha with 30% wintered on the platform, and have operated on a system 4, feeding a little more than 20% supplements On a three-year average before installing the fixed-grid system, that was 3.4t/ha of supplements made up of barley, palm kernel and grass silage. This season that increased to 4.5t DM/ha with more bought in for the higher stocking rate.

Setting up the system has cost them between $6000 and $7000/ha including the removal of the K-line, but Corrigan said it should have a long life. Their investment has led to more pasture eaten and that has helped lift production from a three-year average of 1356kg milksolids (MS)/ha and 364,791kg/year to 1505kg MS/ha and on target for 412,750kg MS for the season.

"There have been economic benefits but we also gained more flexibility in staffing and rosters, so we have some quality of life now."

They still have 130ha of K-line on the farm on a six to seven-day return, which still takes four hours a day to shift, so the goal now is to increase the fixed grid system to 200ha, leaving just 50ha of K-line that would reduce shifting time to two hours or less. The timing of that development has yet to be decided, but Corrigan said it should cost less than the initial fixed-grid setup because the electrical requirements are in place and they will be more efficient with installation.

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