Overhead targeted frost protection

Abstract

This report describes a preliminary investigation into the use of mini-sprinklers attached to overhead laterals for frost protection of fruit trees. The principle aims of this work were to measure the protection efficiency of this technique under New Zealand conditions and to assess its potential advantages and disadvantages when compared with conventional impact-drive sprinkler networks. The ultimate aim is to produce a system which targets water at the trees to be protected, thus virtually eliminating application to inter-row and headland areas. Twenty-nine temperature sensors, in the form of artificial buds, were attached to a tree situated beneath an experimental sprinkler system. The response of these sensors to water application during frosts over the winter and spring of 1984 is described. It is concluded that an overhead targeted system should provide levels of protection comparable with conventional impact-drive networks, while allowing savings in water use of 25 to 45 %. Power requirements would be 60 to 80% less than for a conventional system, with pumps and motors being compatible with those required tor micro-irrigation. Capital costs would be similar or less than those of a conventional system, depending on the need for water storage and the growing method employed. The work also identified bud temperatures during the period prior to ice formation as being potentially limiting when using conventional or targeted sprinkler methods for frost protection on crops exhibiting critical temperatures near 0C. System specifications are discussed and the further work required in order to confirm the viability of overhead targeted frost protection systems and to provide the information necessary for their design is outlined. The need to investigate the potential of the targeted technique for the protection of crops other than stonefruit, particularly kiwifruit, is expressed.