Environmental and Location Effects on Nut Set, Nut Characteristics, and Yield of ‘Ka'u’, ‘Kea'au’, and ‘Keauhou’ Macadamia (Macadamia Integrifolia Maiden and Betche)

Abstract

This three-year study was undertaken to determine the effects of temperature, rainfall, and tree age on nut set, percent kernel, percent grade 1 kernel, and yield of three macadamia cultivars at eight locations in Hawaii. Initial nut set two weeks after anthesis was highest with maximum temperatiires from 18 to 24°C for macadamia cultivars Keauhou, Ka'u, and Kea'au. Increased rainfall in the two weeks after anthesis was associated with a reduction in initial nut set of 'Keauhou' and 'Ka'u', within a range of 1 tb 95 cm of rainfall. Final nut set of 'Keauhou' appeared optimum with a rainfall of 100 cm within a range of 1 to 215 cm during the eight weeks from anthesis to final nut set. As rainfall increased from 1 to 215 cm during the eight weeks from anthesis to final nut set, final nut set of 'Ka'u' and 'Kea'au' was reduced. Final nut set was highest at a minimum temperature of 14°C for all three cultivars. A slight increase of percent kernel of 'Keauhou' and 'Ka'u' was associated with increasing maximum temperatures from 20 to 25°C in the 90 days after anthesis. A reduction in percent kernel of 'Keauhou' and 'Ka'u' was related to maximum temperatures above 26°C. Increasing minimum temperature from 13 to 17°C was related to an increase of percent grade 1 kernels for 'Keauhou'. Percent grade l kernels of 'Keauhou' decreased with increasing age of trees. An increase in percent grade 1 kernels occurred for 'Ka'u' up to 12 years of age, followed by a decline up to 17 years when a more rapid decline occurred. Increasing minimum temperature from 13 to 19°C was associated with increased percent grade 1 kernels of 'Ka'u'. 'Keauhou' had higher yields with rainfall averaging 30 cm per month. Rainfall averaging 10 cm per month for 'Ka'u' and 'Kea'au' was related to higher yields. Average yearly minimum temperatures of about 14.5°C appeared optimum for yield of 'Keauhou'. 'Ka'u' and 'Kea'au' appeared to yield better with about 16 to 18°C average yearly minimum temperature.