THE INFLUENCE OF TREE SIZE CONTROL AND PLANT DENSITY ON CITRUS PRODUCTIVITY

The ability to control tree size is central to the philosophy of high density plantings (HDP) in contemporary horticulture. The method used to successfully achieve this control in Valencia oranges [Citrus sinensis (L) Osb.] propagated on P. trifoliata or on citrange (P. trifoliata x orange hybrid) rootstock was to deliberately inoculate young trees with budline tissue taken from mildly dwarfing citrus exocortis viroid (CEV) infected trees.

The cropping efficiency (Yield/CSA - Kg/m² canopy surface) of trees so grown was not significantly depressed and yields were proportional to canopy surface area (CSA). The yield potential of a citrus orchard was related to the CSA per hectare. A substantial increase in orchard productivity was demonstrated by utilizing HDP of dwarfed "Valencia" orange trees, and no detrimental effects on fruit quality were identified.

Greater productivity was achieved with close within-row spacings (T) for any of the row spacings (R) tested. The data on yield response to given planting densities is described mathematically using an inverse polynomial relation and an optimum yield surface is predicted on the basis of plant density alone.