Effect of irrigation on leaf gas exchange and yield of cashew in northern Australia

Abstract

Gas exchange, leaf water status, soil water use and nut yield of cashew trees were monitored during the reproductive phase in 2 consecutive years (1988 and 1989). Treatment 1 comprised continuous irrigation from the end of the wet season in April until harvest in October; T2, irrigation between flowering (mid June) and harvest; and T3, no irrigation. Irrigation was applied by under-tree sprinkler at 43 mm/week in 1988 and 64 mm/week in 1989. Measurement of leaf gas exchange, chlorophyll content and nut production showed that trees in T2 were as productive as those in T1 (>1.3 kg kernel/tree). In T3, water deficit caused a 4-fold reduction in leaf photosynthesis and reduced leaf chlorophyll content from about 600 to 400 mg/m2 during fruit development. There was no effect on the number of hermaphrodite flowers produced (both ranging from 0 to 15 hermaphrodite flowers/panicle) but the water deficit was associated with a lower kernel yield (1.16 kg kernel/tree). Commercial yields (kg kernel/tree) in irrigated treatments were 20% greater than in the non-irrigated treatment and the kernels from irrigated trees were of a higher grade (kernel recovery >32% in T1 and T2 compared with 27.4% in T3). These results suggest that irrigation of established cashew plantations in the tropical regions of northern Australia can be restricted to the period between flowering and harvest without reducing yield.

Physiology of cashew plants grown under adverse conditions

“…In fact, for dwarf cashew plants cultivated in drier conditions such as that of the semi-arid region of Piaui State, northeastern Brazil, with a low average precipitation, an elevated rate of evapotranspiration and a deep water table -conditions in which the plants would certainly suffer a water deficit -the average photosynthetic rate of the cashew plants was 10 µmol m -2 s -1 (unpublished results). Consistent with these data, Schaper et al (1996) in northern Australia also found significant differences in photosynthetic rates of irrigated and non-irrigated cashew trees, with higher differences during October, when the level of water in the soil was at its lowest and the plants were in full fruit. …”

Influência da irrigação e da localização da inflorescência sobre a expressão do sexo em cajueiro-anão precoce

“…Observou-se, ainda, uma tendência de aumento do número de flores perfeitas abertas nas plantas irrigadas (2,41) quando comparadas às plantas não-irrigadas (2,16), o que sugere que o déficit hídrico provoca a redução do número de flores estaminadas e perfeitas produzidas. O padrão de florescimento observado neste estudo mostrou-se consistente com o obtido por Schaper et al (1996) na região Nordeste da Austrá-lia, em plantas de cajueiro irrigadas e não-irrigadas.…”

“…Relataram, ainda, que após a segunda semana o número de flores estaminadas aumentou acentuadamente, enquanto o de flores perfeitas diminuiu, e, por via de conseqüência, reduziu também a razão sexual durante o restante do perí-odo de florescimento. Schaper et al (1996), também na Austrália, estudando plantas de cajueiro irrigadas por aspersão sob-copa, não observaram efeitos da irrigação no número de flores perfeitas produzidas, as quais variaram de 0 a 15 por panícula.…”

Photosynthetic responses of young cashew plants to varying environmental conditions

“…Nonetheless, both CO 2 assimilation rates values are within the range described for adult cashew trees in other studies. Under natural conditions, Balasimha (1991) and Palanisamy & Yadukumar (1993) reported maximum CO 2 assimilation rates of about 10 µmol m -2 s -1 , while researches in Australia reported values up to 20 µmol m -2 s -1 (Schaper & Chacko, 1993;Schaper et al, 1996;Blaikie et al, 2001). …”

“…The lack of information about the species is due to limited research considering physiological aspects (Marler et al, 1994). Some studies were developed in Australia, such as: Schaper & Chacko (1993), on the influence of leaf age and branch girdling on gas exchange; Schaper et al (1996), on the effects of irrigation on gas exchange and leaf water status; and Blaikie & Chacko (1998) and Blaikie et al (2001), on sap flow and leaf photosynthesis as affected, respectively, by soil drying and irrigation strategies. Balasimha (1991), and Palanisamy & Yadukumar (1993) have also studied the photosynthetic characteristics of adult cashew trees in India.…”