Plant population density and its effects on crop yield and quality have been studied on numerous vegetable crops during the past 30 years [e.g., pickling cucumber (Cucumis sativus) (Cantliffe and Phatak, 1975), zucchini (Cucurbita pepo) (Dweikat and Kostewicz, 1989), muskmelon (Cucumis melo) (Knavel, 1991), pepper (Capsicum annuum) (Stoffella and Bryan, 1988), tomato (Solanum lycopersicum) (Stoffella et al., 1988), snap bean (Phaseolus vulgaris) (Stang et al., 1979), and sweetpotato (Ipomoea batatas) (Schultheis et al., 1999), etc.]. Specifically, plant population density of watermelon has been the focus of many research studies (Brinen et al., 1979; Duthie et al., 1999a, 1999b; Halsey, 1959; NeSmith, 1993; Sanders et al., 1999; Srinivas et al., 1989). However, none of the watermelon studies have addressed the effects of plant population or in-row spacing on miniwatermelons. The introduction of miniwatermelons is recent (Hassell et al., 2007), therefore, information regarding production is scant or lacking. The size requirements for miniwatermelons are specific as most markets require fruit that range between 3 and 8 lb, with the 4- to 5-lb size preferred. Generally, increased plant population densities improve yields until a threshold density is reached for a species, at which time yields level off or decline (Weiner, 1990; Willey and Heath, 1969). This has been found to be the case in most studies with watermelon that involved large-fruited cultivars. Except in one instance, marketable yield increased about 30% when plant (in-row) spacing was decreased from 7.2 to 3.0 ft with ‘Crimson Sweet’ and ‘Starbrite’ watermelon (NeSmith, 1993). Highest marketable yields for ‘Prince Charles’ and ‘Royal Jubilee’ (greater than or equal to 9.9 kg/melon) were obtained when polyethylene mulch was used and areas per plant ranged from 4.3 to 9.7 ft2 (Sanders et al., 1999). Halsey (1959) reported yield increases when area per plant was reduced from 121.6 to 30.1 ft2, while Srinivas et al. (1989) determined that yields were increased when area was reduced from 9.7 to 6.5 ft2. Duthie et al. (1999a) suggested that fruit size decreases more rapidly in cultivars with large fruit than small fruit. Slight variations in miniwatermelon size can result in fruit not being marketable because fruit 1 lb too large will not fit into some packing boxes specifically developed for miniwatermelons. Thus, if fruit production increases with increased plant populations, it is critical that fruit size remain within marketable size constraints so that increased profits may be realized with increasing plant populations.
The goals of these studies were to determine how the cultivars differed and responded to the various plant in-row spacing in terms of percentage of marketable fruit and yields, and if plant spacing impacted internal fruit quality.
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