Tree Spacing of ‘Washington’ Navel Orange1,2

Abstract

Abstract In 1961, trees of Frost Nucellar ‘Washington’ navel orange on Troyer Citrange rootstock were planted at eleven different spacings to determine the effect of tree spacing on growth, production, and fruit quality. Growth rate as measured by trunk circumference was proportional to decreasing tree density or increased spacing. The wider the spacing, the greater was the trunk circumference and the fruit-bearing capacity of the tree. Shading of skirt foliage, as closely planted trees began to crowd, caused the skirts to die and decreased production. Pruning to keep these trees from crowding reduced yield in proportion to the amount of foliage removed. Removal of alternate trees in the two most densely planted spacings, 9 ft. × 11 ft. and 11 ft. × 11 ft., reduced competition and allowed more light to reach the remaining trees. Skirt foliage regrew and yield per-tree and per-acre increased. Fruit colored faster and was larger on the widely spaced trees, where less shading had occurred, than on closely spaced trees. Fruit quality analysis showed no difference in percent of juice, soluble solids, acid, or rag, or in peel and rind thickness. The closest spacings, 9 ft. × 11 ft., 9 ft. × 15 ft. and 11 ft. × 11 ft., operated at a net loss for the first five years of production. Although per tree production was highest on the widest spacing, 22 ft. × 22 ft., net returns per acre on this spacing are still low because of the number of trees per acre. The 11 ft. × 22 ft. spacing with 180 trees per acre had the largest net income per acre.