Spotlight

Agricultural Engineering

By Vicki Hyde, NZSM

Practicality is the name of the game at the Agricultural Engineering Institute based at Lincoln University. For the last thirty years, the institute has prided itself on responding to the engineering needs of the New Zealand farming community.

Initially, the bulk of its work was on checking tractor safety frames, but this has since expanded to areas as diverse as developing irrigation control systems for golf courses and designing netting applicators for vineyards.

Engineers, software specialists and technicians are found in the low-slung brick building and its associated workshops. One shed's machine shop is engaged in tooling up a highly accurate seed dispenser, another holds a sand and polystyrene model of the Rakaia River.

Dr Neil Pasco's office, like many at AEI, is stacked with papers showing the diverse projects in which he is interested. A piece of what appears to be fine leather sits to one side, looking very different from the pulpy nectarine it once was.

The "leather" is fruit leather, a firm sheet of dried fruit pulp that is gaining increasing interest in health food markets. Pasco has been working on a way to reduce the 12-14 hours conventionally needed to reduce 20-millimetre thick fruit pulp to the 6-mm fruit leather.

There were hopes that heating the drying trays electrically would speed up the process, but heat gradients spreading out from the elements caused all manner of problems. The fruit mass would start to sputter like porridge, says Pasco, and you could end up with hot fruit puree all over your face.

Pasco's group used a uniformly heated revolving drum to dry the fruit in four minutes without sputtering or breaking up. It's a continuous process, with fruit being applied at one side and fruit leather scraped off automatically as the drum turns. Announcement of the project brought in other ideas for using the technique, even to producing a form of dried blood with the system.

An experimental mechanical planter holds some hope for the recovery of the fragile, semi-arid lands of the Mackenzie Basin and Central Otago. Technical officer Russell Horrell has spent eight years on pasture establishment methods, trying to find a way to develop land that many have given up on.

"If you can't get the plants established, then the whole system falls over," says Horrell.

The strip seeder gives the seed an excellent start in trying to beat the harsh conditions and competitive weeds. By depositing fertiliser below the seeds, it prevents existing plants in the area from benefiting from the extra nutrients. It breaks up the soil, creating a light tilth suitable for seed growth. Sowing in spring without herbicide, the experimental seeder produced a 52% establishment rate for lucerne compared to the 10% obtained with a standard disc drill.

"We're already getting too many plants," says Horrell. "We could halve the seeding rate."

He's hoping to get continued funding for a second-stage project that's looking at developing more accurate seed placement. Reducing the amount of seed needed is an obvious cost saving.

On a more esoteric basis, but no less practical, is the work being done by AEI's software engineers. They're developing methods of monitoring, analysing and, ultimately, controlling water patterns.

Computer models of how water behaves under certain conditions can tell regional councils what water policies their farming communities should follow, or let golf course managers decide on the best irrigation systems for their greens.

"You have to couch the real world problems in mathematics the software can handle," notes Dr Vince Bidwell. He's been working on developing a computer model of the Canterbury Plains groundwater system and relating this to hard physical data.

"The groundwater aquifer under the central Canterbury Plains is behaving like a large, leaky bucket of stones," says Bidwell. In engineering terms, it's a fairly simple sort of bucket, making it easy to model mathematically.

Other engineers at the institute are using more traditional engineering techniques to fulfill customer requests. Some of AEI's most successful projects were begun as chalk drawings on the floor of the institute's measurement lab.

"It's the biggest blackboard you can find," laughs engineer Lins Kerr.

The space gives the team a chance to assess ideas, walk around possible plans and get a feeling for how to address the problems. One problem involved a local exporter who wanted to increase the planting rate for calla lily bulbs.

The engineering team worked through the requirements and built a prototype out of plywood and sheet metal. It looked something like a ferris wheel, with small buckets for the bulbs revolving around as the rig was towed behind a tractor.

The basic prototype gave them a feel for the design, Kerr says, and gave them a chance to work out the basic requirements. It resulted in a planter that cut acreage requirements by a third, and allowed over 2,000 tubers to be planted per hour.

Kerr, and colleagues John Milne and Geof Warren, also used their practical prototype approach to develop a netting applicator for protective netting for grapevines. Plywood gearing and an electric drill were teamed up to test out their ideas for a simple netting control system.

"I don't believe in spending money on the first prototype," Kerr admits. "We were working towards the philosophy of `let's keep the machine simple', to the extent that anyone can make it."

The final product was the "Birdtex machine" produced to feed out netting produced by Donaghys. A flat platform provides a base for the bagged netting, which is passed through an eye at the top of a mast. From there is it fed out over the vines where it is stretched into place. The whole unit is mounted on a tractor which is driven slowly along the rows to feed out the netting.

The team built a compact model with a two-piece mast to allow it to be taken to Blenheim for a demonstration.

"The grape growers up there couldn't believe it would fit in the back of a station wagon," recalls Kerr.

"When you look at it, you think, `I could've done that myself'," laughs Kerr. "That's a real compliment."

Vicki Hyde is the editor of New Zealand Science Monthly.