SEASONAL CHANGES IN PEAR TRANSPIRATION

Abstract

Flood and sprinkler irrigation systems in Australia have largely been replaced with micro-irrigation. Understanding crop water requirements in these orchards is necessary to avoid over- and under-irrigation so that yield and water are optimized. The objective of this study was to investigate seasonal changes in pear transpiration (T) and link this to reference crop evapotranspiration (ETo) and intercepted photosynthetically active radiation (fPAR). The sap flow technique was used to determine T in a commercial high-density 'Williams' Bon Chretien' pear (Pyrus communis L.) orchard. Measurements were taken at 30-minute intervals using the compensation heat-pulse method and commenced prior to full bloom. ETo was calculated from local weather data measured at the orchard site. fPAR was estimated from an array of 24 PAR sensors positioned on the orchard floor. Daily T increased after full bloom and stabilised at approximately 3 mm/day in late spring and early summer when irrigation was deliberately withheld. Daily T increased to a maximum of approximately 5 mm/ day when irrigation was applied during the period of rapid fruit growth and ETo was high. After harvest, daily T steadily declined. A strong relationship between daily T and fPAR-weighted ETo was found for the period of full irrigation prior to harvest (T = 1.1 fPAR ETo; R2 = 0.76). Daily T during the withholding irrigation and post harvest periods was generally less than daily T based on the relationship established under full irrigation prior to harvest.