Production of crops in greenhouses is an intensive agriculture production system (Stanhill and Enoch, 1999) because more labor and materials are required than in open-field systems. Because investment and production costs are substantially higher in the greenhouse than in the field, methodologies used to produce greenhouse crops require more efficiency than those used in traditional field systems. Success of any greenhouse vegetable system relies on the production of greater fruit yields and better fruit quality. These higher yields are dependent on cultivar, crop management system, and growing season (Jensen and Malter, 1995; Lorenzo and Castilla, 1995). Because of the higher costs for materials and labor, careful consideration of optimum plant populations for soilless greenhouse crops is essential (Logendra et al., 2001).
Protected agricultural systems, such as passively ventilated greenhouses, could benefit vegetable growers in Florida (Cantliffe et al., 2001). Crops should be of high value and grown in efficient production systems to ensure that high returns are gained in relation to investment costs. New greenhouse crops such as Galia muskmelons could open new markets for future and existing greenhouse growers in Florida and other greenhouse production areas of the United States.
Muskmelons grown under greenhouse conditions at optimum plant populations and cultural practices can result in higher fruit production than field-grown crops (Waquant, 1974). Greater fruit yields may occur under greenhouse conditions than field systems because plants can be arranged more uniformly, avoiding large gaps between plants and rows while simultaneously optimizing light interception. Soilless culture and vertical plant growth (trellising) can improve available light interception, air movement, and microclimates of each plant, as well as promote the efficient use of water and nutrients through precise irrigation and recycling methods.
Because of the high investment costs, greenhouse production systems require selecting plant populations that make efficient use of all available space. Although spacing combinations between plants and between rows could result in high marketable yields per unit area, minimum space between rows is limited by the width of ladders and carts required for cultural practices such as pruning, training, pesticide application, and harvesting (Papadopoulos and Pararajasingham, 1997).
Under field conditions, muskmelon yields may be improved by increasing plant density (Maynard and Scott, 1998; Nerson, 2002). Although higher plant populations may result in increased marketable yield per unit area (Paris et al., 1985), the number of fruit per plant and fruit size are often reduced (Kultur et al., 2001). In field experiments conducted in north–central Florida, planting densities of 1.0, 2.0, and 3.0 plants/m2 of Galia-type muskmelons did not affect fruit yield (Paris et al., 1988). Soluble solids content (SSC) of muskmelon grown at higher densities has been reported to decrease as plant density increased from 2.0 to 8.0 plants/m2 (Mendlinger, 1994), whereas others reported no difference in SSC from fruit grown at 3.6 and 7.3 plants/m2 (Kultur et al., 2001).
Galia-type muskmelons planted in the field at plant densities of 1.0 and 2.0 plants/m2 resulted in yields of 1.8 and 2.1 fruit/m2 respectively (Paris et al., 1988). Total fruit weight at both plant densities was ≈2.3 kg·m−2. Although more fruit per unit area were produced at the higher density, mean fruit weight per plant was less. Nerson et al. (1984) reported 20% greater yields of field-produced Galia muskmelon at 3.1 plants/m2 than at 1.4 plants/m2; however, mean fruit weights were similar. The European market desires a Galia fruit size around 1.0 kg; therefore, higher densities may result in more desirable yields for certain markets (Ban et al., 2006). Galia muskmelon yields greater than 4.5 kg·m−2 were produced under field conditions in north–central Florida (Hochmuth et al., 1998). A muskmelon yield of 9.4 kg·m−2 was reported when plants were grown in walk-in tunnels using perlite soilless culture (Waldo et al., 1997).
Shaw et al. (2001) reported that Galia muskmelons grown in a passively ventilated greenhouse using perlite soilless culture can produce 9 to 15 fruit/m2 at a plant density of 3.0 plants/m2. Individual plant yields ranged from 3 to 5 fruit/plant with a mean fruit weight of 1.2 kg/fruit (≈14.0 kg·m−2). Consequently, yields were greater than those produced by plants grown in either walk-in tunnels (Waldo et al., 1997) or by field cultivation (Hochmuth et al., 1998).
Reports from countries where Galia melon is commercially produced indicate that yields of 4.3 to 5.9 kg·m−2 are generally achieved under protected structures (e.g., tunnels and greenhouses) using soil. These yields are common in Israel (Arava Desert) at a planting density of 1.3 plants/m2 (Hecht, 1998; Z. Karchi, personal communication). Galia produced in Spain at a plant density of 2.0 plants/m2 using coconut coir and rockwool as soilless media yielded 12.7 kg·m−2 (Torres and Miguel, 2003).
Production of Galia muskmelons in passively ventilated greenhouses in Florida using soilless culture may result in profitable yields when optimum plant densities are used. Selection of plant densities that efficiently use available growing space and labor may make it possible to obtain a greater yield and positive return on investment. The objective of this experiment was to evaluate the influence of plant density on fruit yield and quality, plant growth, and net return of Galia-type muskmelons grown in a passively ventilated greenhouse in Florida.
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