Vol. 71 No: 4

Title:
Winter Irrigation Increased Yield of ‘Washington’ Navel Orange (Citrus Sinensis L. Osbeck)

Authors:
ANWAR G. ALI and CAROL J. LOVATT

pp: 653-660

Abstract:
The present study aimed to quantify the effect of withholding irrigation during the winter season in southern California on the productivity of ‘Washington’ navel orange and to determine whether the additional expense of irrigating navel orange trees during the winter is a cost-effective production management strategy. Yield and fruit size were quantified for 30 year old ‘Washington’ navel orange scions on Troyer citrange rootstock which were rain-fed from October 1 to March 1 in each of three successive years and for another set of trees which were irrigated during the winter. Supplementing winter rainfall with irrigation significantly increased the weight of fruit per tree in all three years of the study (45 ± 17 kg fruit tree^-1, n = 3 years) and number of fruit per tree in the two years in which the rain-fed, -winter irrigation trees had significantly lower predawn water potentials than the +winter irrigation trees. Despite the yield increases which resulted from supplementing winter rain with irrigation in each year of the study, there was no reduction in the number of commercially valuable fruit with tranverse diameters between 7.0 to 8.0 cm in any year (P≤0.05). Trees receiving winter irrigation to supplement rainfall were less affected by a preharvest freeze: compare a 50% reduction in yield from the previous year for the +winter irrigation treatment to a 93% reduction for the -winter irrigation trees. Irrigation treatment did not affect tree nitrogen status. Even in the year when the lowest net increase in yield was obtained with the greatest amount of irrigation water, valued at a high cost for California, winter irrigation was a cost-effective management strategy for the production of ‘Washington’ navel orange.

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