Transpiration coefficient and ratio of transpiration to evapotranspiration of pear tree (Pyrus communis L.) under alternative partial root-zone drying conditions

Transpiration coefficient K_cb, crop coefficient K_c, and the ratio of transpiration to evapotranspiration (T/ET) are important parameters for pear orchard irrigation management and may vary with different methods of irrigation. This study investigated their changes under three irrigation methods: conventional flood irrigation (CFI), fixed partial root-zone drying and irrigation (FPRD) and alternative partial root-zone drying and irrigation (APRD), in a semi-arid region of Victoria, Australia. The average seasonal ET was 865.29, 795.63 and 804.72 mm respectively for CFI, FPRD, and APRD with ET₀ of 817.59 mm for the pear fruiting season. The seasonal transpiration accounted for 81.1%, 84.4%, and 84.1% of evapotranspiration for CFI, FPRD, and APRD respectively. For the CFI, FPRD, and APRD treatments, the seasonal average K_c were 1.058, 0.973, and 0.984 (with their maximum values of 1.326, 1.211, and 1.257) respectively similarly, the respective seasonal average K_cb were 0.858, 0.822, and 0.828 (with maximum values of 1.059, 1.024, and 1.054). The relationships between K_cb, K_c, T/ET, and days after the season beginning were fitted to a fifth-order polynomial equation with higher coefficients of determination R². The maximum K_c and K_cb occured in mid-January. The ratio T/ET varied from 0.736 to 0.909, 0.743 to 0.947, and 0.741 to 0.925 in the pear fruiting season for CFI, FPRD, and APRD treatments respectively. Results suggested that APRD and FPRD can improve the ratio of transpiration to evapotranspiration, and reduce transpiration coefficient and crop coefficient. Such effects should help improve of water-use efficiency in pear orchards.