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  • Author or Editor: Merle Jensen x
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A major threat to the continuance and expansion of the greenhouse industry in the U.S. is the rising cost and availability of fuels to heat greenhouse units. While the greenhouse industry is a relatively small part of agriculture in the United States, it is important as it provides high-quality products on a year-round basis rather than being seasonally restricted. The industry produces not only vegetables, but an array of floricultural crops that enhance the esthetic beauty of our environment.

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Homes of the not-too-distant future may have their own year-round vegetable gardens in greenhouses that double as solar energy collectors. Such a demonstration is presently in operation at the Environmental Research Laboratory (ERL) of the Univ. of Arizona and is funded by the Energy Research and Development Administration (ERDA) and the Agricultural Research Service of the U.S. Department of Agriculture. The model is a research and development tool to evaluate the economic and environmental desirability of developing such a unit as part of residential buildings to reduce the requirements for fossil fuels and at the same time enhance the home environment and add an increment of food production potential.

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Cherry tomato (Solanum lycopersicum var. cerasiforme) plants were grown hydroponically with three different regimes of electrical conductivity (EC) of the nutrient solution to develop an effective EC management method to enhance the fruit quality. The EC treatments examined were 1) continuous high EC [4.7 dS·m−1 (HE)], 2) continuous low EC [2.8 dS·m−1 (LE)], and 3) high EC combined with midday (1030–1530 hr) low EC [midday reduction of high EC (MDR)]. The research was conducted to obtain preliminary information on the effect of EC treatments on the yield and fruit quality for 15 weeks of harvest under semiarid greenhouse conditions. Harvested fruit were sorted to several quality grades, including the “premium” grade based on fruit size, color, and total soluble solids. The number of fruit per truss was significantly higher in cultivar L308 than in cultivar L907 and in the LE treatment than in the HE or MDR treatment. The fruit size decreased over time regardless of EC treatment and cultivar. Cumulative yield of 15 weeks was greater in the LE treatment (26.3 kg·m−2) than in the HE treatment (22.1 kg·m−2) for ‘L907’, and there were no significant differences between the three EC treatments for ‘L308’ (24.1–28.1 kg·m−2). The cumulative yield in the MDR treatment was similar to that in the LE treatment regardless of cultivar. When quality attributes such as total soluble solids concentration measured for randomly sampled fruit were considered, cumulative premium-grade yield was the greatest for the HE treatment (12.9 or 17.6 kg·m−2) and was the smallest for the LE treatment (1.4 or 12.1 kg·m−2), regardless of cultivar. The cumulative yield of premium-grade cherry tomatoes in the MDR treatment was not significantly different from that in the HE treatment for ‘L308’ but was 11% less than that in the HE treatment for ‘L907’. Therefore, together with cultivar selection, the MDR treatment may be a potential alternative to a more commonly practiced continuously high EC treatment in semiarid greenhouses with limited environmental control capacity in which increasing the nutrient EC to increase quality is desired without significantly decreasing yield.

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Many of the world's desert areas remain uninhabited but could be made productive, even attractive for settlement, if certain necessities were present. One such necessity is food. If crops are to be grown, water for irrigation and an environment conducive to good crop production are needed. Water is not available in most desert regions and must be provided together with the required power to pump this water from wells and into the area of crop production. The daily temperatures in most desert areas are adequate for crop production during most months of the year, but such hazards as sandstorms and insect invasions often make them undesirable for vegetable production; and providing water for irrigation is expensive. Experiments now are being conducted by the Universities of Arizona and Sonora in the growing of vegetables in controlled-environment, air-inflated greenhouses. The experimental unit is located in Puerto Penasco, Sonora, Mexico, on the east coast of the Gulf of California. The following are procedures and results obtained to date from tests which have been in progress since October 1968 (Fig. 1, 2).

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