Institute examines frost protection

Press, 20 July 1984, Page 21

Institute examines frost protection

Fighting frost damage to horticultural crops is the object of a 5120,000 research programme under way at Lincoln.

Researchers at the Agricultural Engineering Institute at Lincoln are experimenting with two methods of frost protection — a targeted overhead sprinkler system and undertree sprinklers. Undertree sprinklers, which apply water to the ground below the tree canopy, have been used to fight frost in the United States for some years, and have attracted keen interest from some New Zealand orchardists.

This method appeals to growers because overhead systems can lead to disease problems, caused by the wetting of fruit and foliage. Undertree sprinklers can also double as an irrigation unit in summer, cutting equipment costs. Growers in the Blenheim district have already installed an estimated 80ha of undertree sprinklers, but researchers at Lincoln are concerned at the rapidly growing investment in this type of system for frost protection. Dr Peter John, leader of the agricultural engineering institute’s soil and water division, said orchardists were spending a lot of money on undertree frost

protection systems with no guarantee that they would work. Dr John said there was very little information available on how effective undertree frost protection was, how it worked, or what design criteria should be used. Until it was known how the method worked, a system could not be designed to suit the conditions. The institute has received dozens of inquiries about the system in recent months, but researchers have been unable to answer questions fully or make any recommendations. This prompted the setting up of a trial to look at the effectiveness of undertree sprinklers in Canterbury conditions. Two identical blocks, 110 metres in diameter, of established apple trees on Lincoln College’s orchard have been fitted with undertree sprinklers and temperature sensors to record the effectiveness of the system. When the temperature drops below 0 deg. C, the sprinklers are automatically activated on one block and the other block acts as a control The roles of the blocks are alternated each night. The sprinklers have an application rate of water of about 3mm per hour. The temperature sensors record the air and bud tempera-

tures in both the irrigated block and control. Mr Peter Carran, a senior research officer, said it was too early to say how effective the undertree system was in preventing frost damage. Frosts during spring when the developing fruit was most vulnerable would give a good indication. Overhead sprinklers have been used for frost protection for several years, but most systems use standard irrigation equipment which delivers large volumes of water. At Lincoln, researchers are testing a modified over-

head system using microsprinklers to target a fine spray directly on to crops rather than over the whole growing block, including the rows between crops. Because less water is applied, mud and drainage problems could be reduced. A major advantage in using a targeted overhead system lies with a reduction in the amount of water ■required, which can mean savings in pipe sizes and water storage facilities. Overhead sprinkler trials are being carried out on the college’s stonefruit block. As with the undertree trial,

sensors measure the air and bud temperatures. Dr John said the research team hoped to be able to comment on the viability of the two frost protection systems before next winter. Funds for the research programme are being provided by the institute, Ministry of Works, D.5.1.R., Ministry of Agriculture and Fisheries, and the Fruitgrowers’ Federation. Another weapon in the fight against frost is a fog generator being studied by the institute in an orchard at Hamilton. Called a frost rocket, it was invented by a Hamilton

orchardist The rocket makes fog by atomising water and blowing it over an orchard, creating a blanket similar to conditions on a cloudy night It is claimed to be able to spread fog over a 100-metre radius.

A seminar at Alexandra for Central Otago fruitgrowers was told recently that waterlogging of soils had become an increasing problem in Central Otago orchards during the last 10 years because of overhead sprinklers. Mr Graham Hutchinson, a farm adviser with the M.A.F. at Alexandra, said the use of overhead sprinklers for frost protection meant that large amounts of water were being applied in spring. This was a period when conditions would already be fairly moist, evaporation was low and irrigation was not necessary. When combined with poor drainage, this resulted in the soil around fruit trees becoming waterlogged and cold. A lack of oxygen to the roots could restrict growth and kill the trees. Stonefruit trees succumbed more readily to waterlogging than pipfruit Improved drainage to remove excess water, combined with efficient irrigation management, would go a long way to preventing these problems, said Mr Hutchinson. Improved drainage would lead to greater tree vigour, resulting in higher yields and better quality fruit.