Jul 18, 2008
New Zealand Processor Fights Freezing

Fruit growers have used wind machines for years to prevent frost damage during the first appearance of buds through flowering. A New Zealand-based grower and processor is using the technique to extend the growing season of baby spinach, a move that will reduce costs and add to the company’s sustainability efforts.

New Zealand Fresh Cuts, based in the country’s largest city of Auckland on the North Island, constructed a wind machine in the Rangiriri growing area that will allow the processor to grow a better quality crop of leafy greens year round. A 35-foot tower with 17-foot blades circulates the air over a 14-acre area, protecting 900,000 leafy green plants from frost, according to the company.

Fresh-cut salads from New Zealand Fresh Cuts have always been available year round, but the company had to import some of the leafy greens and the growing areas that do have year-round production had to overplant to make up for frost damage.

“We were offering salads all year round, but were often having to short supply orders or air-freight in raw materials at a loss to cover our customers’ requirements. We also had to plant significantly higher quantities of lettuce to allow for the damage caused by heavy frosts,” said Marilyn Tregidga, communications director for New Zealand Fresh Cuts.

Sustainability is important to the grower and processor, and construction of the wind machine will improve the company’s efforts.

“The wind machine allows us to significantly reduce wastage both on the farm and at the processing plant, as we have significantly reduced the amount of produce we are having to discard due to frost damage and then subsequent bacterial colonization,” Tregidga said. “The flow-on effects of this are less fuel usage, reduced tillage, reduced nitrogen requirements and more sustainable land use with less buildup of disease in the soil. It has also allowed us to consolidate our growing operations onto one farm, allowing us to reduce operational costs without the geographical frost risks we were faced with. Allowing us to grow on better, free-draining soils in more frost-prone areas has also been an advantage.

“The wind machine will allow us to grow year round on the one property in an economically sustainable way, and the design of the wind machine allows for it to be easily moved to aid crop rotation programs as well.”

A local company that has designed and installed wind machines for fruit growers handled construction, but the technique hadn’t been used on leafy greens before. A wind machine can prevent frost damage during a radiation freeze, when cold, dry air settles in the absence of wind and cloud cover at night. The air forms layers, with cooler air settling near the ground, trapped by a warmer layer 30 feet to 50 feet off the ground. That upper layer can be 3º F to 10º F warmer, but the cold air trapped below it will continue to cool and settle in low-lying areas. Because there is little air movement, exposed plant parts can be even colder than the surrounding air, causing further freeze damage. The wind machine will break up those air layers and pull warmer air down to the plants to protect them from frost damage.

“We relied heavily on the expertise of a local company specializing in wind machine design for frost fighting applications,” Tregidga said. “Their previous experience has been in spring frost control of mainly stone and pip fruit, so winter frost control on lettuce was new to them. We have had to undertake extensive trials of the effective use of the inversion layer (air) so we can get the maximum possible frost protection (for) as long as possible, as many of our frost events are over 12 hours in duration. This leads to challenges in using the inversion layer carefully, without pulling it all down too quickly.”

If the technique works for leafy greens as well as it does for fruit growers, New Zealand Fresh Cuts will be able to supply its customers with a fresher, locally grown product. The capital investment will reduce the frost risk in the best winter growing areas, reducing overproduction and waste from frosts. With winter just around the corner in the Southern Hemisphere, the processor should immediately benefit from its innovation in adapting new techniques and technology to the production of leafy green vegetables.

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