Transpiration of Pear Trees and Implications for Irrigation Scheduling

摘要

Lack of water for irrigation due to changing climate is emerging as the biggest threat to the viability and sustainability of the pear industry in Australia. Using less irrigation, maintaining productivity and clearly demonstrating eco-efficient irrigation can be achieved by a better understanding of crop water requirements in different environments, tree training and trellising systems, and management scenarios. Crop water requirements in high-density pear orchards were investigated by relating transpiration (T) measured using the sap flow method, to reference crop evapotranspiration (ET0) and effective area of shade (EAS) in two commercial 'Williams' Bon Chretien' pear orchards. EAS was estimated from photosynthetically active radiation (PAR) sensors installed in a grid pattern between trees and rows on the orchard floor. Seasonal changes in T increased after full bloom to reach a maximum in mid-summer and then steadily declined in late summer and autumn. EAS remained relatively constant at 0.6 in both orchards for most of the season apart from the first 30 days after full bloom and at leaf fall. There was a similar positive linear relationship between daily T and EAS-weighted ET0 in both orchards for pre-and postharvest data excluding the period of withholding irrigation when trees were likely to be water stressed. The results suggest that full irrigation of pear trees can be estimated from 1.1 EAS ET_0 up to harvest. Postharvest full irrigation requirements appear to be less and can be estimated from 0.8 EAS ET0. Our measurements showed that EAS remained relatively constant over the irrigation season making the task of scheduling much easier, with simple recommendations based on a single measure of EAS and an ET_0 deficit.