Densely Planted Okra for Destructive Harvest: III. Effects of Nitrogen Nutrition

Abstract

Research was conducted to develop a cultural system that would permit a destructive mechanical okra [Abelmoschus esculentus (L.) Moench] harvest. Okra grown at a highly dense (HD) plant population of 25 × 23 cm and destructively harvested by machine was compared with control plants spaced at 90 × 23 cm and repeatedly and non-destructively harvested by hand. The control N fertilization regime was 45 kg·ha-1 of N preplant, followed by one or two topdressings, each with 22 kg·ha-1 of N. Treatments applied to HD plots were designed to be multiples of the control N fertilization levels. Preplant fertilizer was added such that the sum of residual soil N plus the added fertilizer would total to 45, 90, or 135 kg·ha-1 of N for the standard, intermediate, and highest rates, respectively. Topdressing rates were 22, 44, or 66 kg·ha-1 of N for standard, intermediate, and highest, respectively. Topdressing was timed to follow a mechanical harvest of the HD plots. Since there was only one mechanical harvest in the two 1995 studies, topdress N treatments did not affect yields from mechanical harvest in that year. Nitrogen treatments had few effects on fruit yield per hectare of HD okra, even when stem N concentrations equaled or exceeded those of control plants. The highest N rate tended to delay fruit production. Increasing N rates did not affect the marketable fruit yield obtained by mechanical harvest of HD plants expressed as a percentage of the total cumulative marketable fruit yield from control plants. Physiological factors appear to be limiting the potential for densely planted okra in a destructive mechanical harvest system rather than horticultural factors such as N nutrition.