MICROCLIMATE MODIFICATION IN PEAR PLANTATION BY USING COOLING IRRIGATION

Irrigation in some countries is a horticultural practice mainly used only to supply water. At the same time the use of micro-sprinklers have a powerful influence on the changes of temperature in orchards. When the air temperature is high (~20°C or higher) evaporative cooling from irrigation significantly decreases the plant surface temperature and air temperature. The cooling effect is stronger when the air is dryer. By using cooling irrigation regularly, canopy temperature can be decreased so that the beginning of bloom can be delayed. Also if the bloom is early and frost probability is high, serious damages can happen in orchards. The beneficial effect of cooling irrigation is the temperature reduction and frost protection. In March 2010, one month before expected bloom, an irrigation system was established to produce anti-frost treatment and regulate the micro-climate of a ‘Bosc’ pear orchard which belongs to the University of Debrecen (Hungary). The objective of sprinklers was to cool the air by increasing water evaporation and relative humidity. The position of the micro-sprinklers was planned in three levels (around the tree trunks, a few cm near to the soil surface, in the crown region and above the crown, 0.5 m higher). The results showed that the water sprayed in the orchard by micro-jets influenced the temperature decisively. At higher temperatures (~20°C), temperature reduction may attain 5-7°C. Low relative humidity of the air may increase the relative effect. When water was applied at intervals of 15 min ten times per day from 8:00 to 18:00, the air, flower and bud surface temperatures could be kept low. When the temperature was higher than 10°C, irrigation was used at night in similar 15-min intervals, from 18:00 to 6:00. The beginning of bloom could be delayed for more than ten days. ‘Bosc’ pear blooming dynamics were characterized by a logistic curve in the treated as well as in the control plot. In the treated plot, the curve was steeper than in the control in spite of the equal temperatures measured in the plots. Under Hungarian climatic conditions, the method was successfully used to delay bloom dates. The main result was the diminution of the frost damage in the spring that assured pear yields.