Poor response of macadamia (Macadamia integrifolia Maiden and Betche) to irrigation in a high rainfall area of subtropical Australia

Abstract

Bearing macadamia trees (cv. Keauhou 246), received varying rates of irrigation at weekly intervals over 8 years, and the effects on nut yield and tree size were measured. Annual rainfall ranged between 1232 and 2283 mm and was supplemented by 9-24 irrigations per year. Unsatisfied evaporative demand in the control treatment was estimated to vary from 1 to 380 mm per season. Canopy and trunk areas were not affected by irrigation. The average annual yield per unit of canopy area across all treatments was about 900 g/m2 of nut in shell. Irrigation reduced nut in shell yield per unit trunk area slightly, and depressed the individual mean weight of nut in shell by an average of 5%. There was a highly significant (P<0.01) inverse linear relationship between individual nut weight and irrigation amount, with an individual mean nut in shell reduction of 7% at the highest irrigation rate. Kernel weight, as a percentage of total nut in shell weight (kernel recovery), was not affected by irrigation, but the percentage of kernels that floated in tap water (grade 1 kernels) was 2.8% higher from control trees than from irrigated trees.