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- Author or Editor: Daniel H. Willits x
In the southern U.S. and other mild winter areas, the length of the harvest season for greenhouse tomatoes is limited by high night temperatures. The purpose of this study was to determine the extent of this limitation by installing mechanical refrigeration to provide nighttime cooling in two of four computer-controlled greenhouses. For three crops of greenhouse tomatoes, nighttime temperatures in cooled houses were not allowed to rise above 20°C. Sixteen-week old transplants were placed in greenhouse treatments starting Mid-April ('91), mid-July ('90) and mid-August ('89). Fruit weights were significantly increased by nighttime cooling on all three planting dates, with weights increasing 11%, 28% and 53%, respectively. For the mid-July and mid-August plantings, fruitset, fruit size and % uncracked fruit were also increased significantly by nighttime cooling. Data collected in '90 showed that plants in the cooled houses required only an additional 2.4 days to mature and were only 10-15% taller, suggesting there were no significant plant-related disadvantages to nighttime cooling. Lack of stored heat and nighttime heat load in the greenhouses resulted in low cooling costs and refrigeration requirements, so nighttime cooling may also be commercially feasible.
Previous greenhouse studies in Raleigh have shown that nighttime cooling increases tomato fruit weights from 11% to 53%, depending on planting dates. The physiological mechanism was unclear, except that temperatures during fruitset were most critical. We report here on 3 experiments, 2 in greenhouses and 1 in the phytotron, comparing pollen characteristics of plants grown at differing night temperatures. In the greenhouse studies, nighttime temperatures were kept below 20°C for either the whole night or just the last half of the night. In the phytrotron studies night temperatures were 18, 22, 24 or 26°C, In both phytotron and greenhouse studies, there was considerable day-to-day variability in pollen characteristics and % germination. The most consistent effect in both types of studies was a decrease in total pollen and an increase in % abnormal pollen at high night temperatures. In the phytotron studies 20°C appeared optimal for both these characteristics.
Eight tomato (Lycopersicon esculentum) cultivars were grown for 16 weeks in greenhouses enriched for an average of 8.1 hours daily to 1000 μl CO /liter of air or in greenhouses maintained at ambient CO. Carbon dioxide enrichment significantly decreased the mean number of greenhouse whiteflies [Trialeurodes vaporariorum (Westward), Homoptera: Aleyrodidae] as measured by counts from commercial yellow sticky traps. The number of whiteflies present was negatively correlated with both seasonal foliar C: N ratio and percent C but positively correlated with percent N in the foliage. Thus, CO enrichment apparently alters plant composition in such a way as to reduce significantly the population growth of greenhouse whiteflies.
Commercial recommendations exist for using short-term salt-shocks on tomato (Lycopersicon esculentum Mill.) to improve fruit quality. Six experiments were conducted to 1) assess the influence of nutrient concentration and short-term salt-shocks on fruit quality and yield and 2) identify a vegetative predictor of subsequent fruit quality. The first objective was addressed in three nutrient film technique (NFT) experiments (Expts. 1-3). Four treatments were applied: two maintained constant at two baseline concentrations (0.25X and 1X-commercial level) and two provided salt-shock periods of 30 min, twice daily. There were no effects of baseline concentration or salt-shocks on total number and weight of marketable fruit. Fruit quality was better at the 1X baseline concentration as observed by higher titratable acidity (Expt. 2), higher percent dry matter (Expts. 2 and 3), higher soluble solids concentration (Expt. 2), and lower pH (Expts. 2 and 3), however, weight per marketable fruit was lower (Expt. 2). Salt-shocks had little effect on fruit quality, refuting its commercial potential. Salt-shocks decreased fruit pH (Expts. 1 and 3). However, titratable acidity increased at the 0.25X level and decreased at the 1X level (Expt. 3). In Expt. 2, but not in Expt. 3, citrate concentration in the fifth leaf from the apex of young vegetative plants was correlated with subsequent fruit quality. Three additional experiments in static hydroponics with vegetative plants showed no significant differences in leaf citrate levels due to a single, short-term salt-shock. Thus, citrate is not a good predictor of fruit quality.
The total costs of producing Easter lilies (Lilium longiflorum, Thunb.) were developed for firms with 1,800 m2, 9,000 m2, and 36,000 m2 of production area. Economies of size existed in 2 market channels (mass market and full service florist). The total costs of Easter lilies to producers in the mass market marketing channel, including the cost of 6.31% bulbs that did not emerge, were $2.08, $1.83, and $1.63 per pot for the 1.800 m2, 9,000 m2, and 36,000 m2 firms, respectively. Costs were $0.48, $0.36, and $0.32 higher per pot for the florist producers than for the mass market producers for the small, medium, and large firms, respectively.
Economic efficiencies were greatest in peak sales periods in surveyed floricultural firms selling both to retail florists, and mass markets. Efficiency decreased in intermediate and slack sales periods. About the same procedures were followed in each time period, but sales were reduced in intermediate, and slack periods. Surveyed firms selling to mass markets sold bedding plants during peak periods which required no variable labor or capital marketing inputs; thus, they were more technically efficient than firms selling to retail florists during the peak period. Economies of size were found in the retail florist channel but not in the mass market channel. Maximum economic efficiency was reached at a smaller size by firms selling to mass markets, indicating that the mass market channel was more competitive in the marketing function than was the retail florist channel. Large differences in technical efficiency were found within groups, indicating that increased profit could be made by the least efficient firms adopting the efficient technology of the most efficient firms within the same group. Within groups, the most efficient firms utilized more fully their fixed inputs than did the least efficient, and were thus able to expend a reduced percentage of sales on variable inputs. A persistant problem for the least efficient firms, especially during slack periods, was a delivery cost larger than that of the most efficient firms resulting from an increase in distance and number of stops.
The effect of CO2 concentration (330 and 675 μL·L−1) and photosynthetic photon flux (PPF) (mean daily peaks of 550–1400 μmol·m−2·s−1) on total mineral contents in shoots was studied in chrysanthemum [Dendranthema ×grandiflorum (Ramat) Kitam ‘Fiesta’] during three times of the year. Growth (as measured by shoot dry weight) and shoot mineral contents (weight of nutrient per shoot) of hydroponically grown plants were analyzed after 5 weeks. There was a positive synergistic interaction of CO2 concentration and PPF on growth with the greatest growth at high PPF (1400 μmol·m−2·s−1) with high CO2 (675 μL·L−1). When growth was not used as a covariate in the statistical model, both CO2 concentration and PPF significantly affected the content of all eight nutrients. However, after growth was included as a covariate in the model, nutrients were classified into three categories based on whether CO2 concentration and PPF level were needed in addition to growth to predict shoot nutrient content. Neither CO2 concentration nor PPF level was needed for Mg, Fe, and Mn contents, whereas PPF level was needed for N, P, K, and Ca contents, and both CO2 concentration and PPF level were required for B content.