Plant Density‐Dependent Variation in Marketable Yield, Fruit Biomass, and Marketable Fraction in Watermelon

Abstract

An improved knowledge of effects of density of plants on yield of watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] would help efforts to determine optimal planting density and to anticipate the economic impact of factors that reduce density. We conducted a series of experiments to determine plant density‐dependent rates of change of marketable yield, fruit biomass, and marketable fraction in watermelon cultivar Sugar Baby. In single‐row plots, at least 3.7 m apart, density varied from 0.4 to 4.1 plants m2 (1000‐9000 plants ha−1). Marketable yield per unit area increased at linear rates of 0.5 to 1.1 Mg ha−1 per thousand plants ha−1 because fruit biomass increased at linear rates of 1.1 to 3.2 Mg ha−1 per thousand plants ha−1. The linear effect of plant density explained more than 90% of the increase in fruit biomass per unit area in most experiments. Density did not affect the fraction of fruit biomass that was of marketable quality. The linear rate of change in the marketable fraction did not exceed 3% per 1000 plants ha−1 on average in any experiment. Per plant, marketable yield and fruit biomass, respectively, decreased at curvilinear rates of 0.8 to 8.6 and 1.4 to 10.8 (kg plant−1 per thousand plants ha−1) (plants ha−1)2. These decreases were consistent with a constraint due to intraspecific competition. Our results support the hypothesis that efficiency of commercial production of watermelon could be increased by increasing planting densities.