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Athanasios P. Papadopoulos

The greenhouse cover has previously been shown to have large effects upon the greenhouse environment, crop productivity and energy use. However, in most cases, because of inadequate treatment replication, the extent of these effects has been impossible to quantify with confidence. In the fall of 1987, a new greenhouse complex of 9 mini greenhouses (6.4m × 7.2m, each) was constructed at the Harrow Research Station on the principles of the 3×3 Latin Square experimental design and with glass, double polyethylene film and double acrylic panel greenhouse covers as the three levels of treatment in the Latin Square. During the spring seasons of 1988 and 1990 the greenhouse cucumber cultivar Corona was cropped in rockwool in all 9 mini greenhouses, under 3 day air (DAT: 18°C, 21 °C and 24°C) and 3 night air temperatures (NAT: 16°C, 18°C and 20°C), superimposed across the rows and columns of greenhouses, respectively, to estimate yield and energy use response to DAT, NAT and greenhouse cover variation. Early marketable yield was highest at the 18/18 and 18/20°C DAT/NAT combinations and final marketable yield was highest at 18°C DAT regardless of NAT. Yield differences due to the greenhouse cover were insignificant. However, there were consistent differences in greenhouse air RH due to greenhouse cover (60%, 70% and 75% daily averages for glass, double polyethylene and double acrylic, respectively). Also, there were significant energy savings with the use of double polyethylene or double acrylic, as compared to glass greenhouse cover, and with low DAT and NAT (28%, 15% and 12% energy use reduction, respectively).

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Athanasios P. Papadopoulos

Horticultural crop management strategists of the past have routinely chosen to remove root-related limitations to productivity by operating at high fertility levels and by excessive irrigation of well-drained soils, without much concern for fertilizer losses to the environment. The relatively low cost of fertilizer as a component of the overall production cost has justified, at least on economic tens. the liberal application of fertilizer on most horticultural crops. However, inefficiencies in fertilizer use can no longer be neglected as society becomes increasingly aware and critical of the valuable energy expended in fertilizer manufacturing and of the damage to the environment from runoff fertilizer. Progress made towards fertilizer use economy will be discussed in relation to the development and use of computer controlled fertilizer injectors which allow the timely application of precise amounts of nutrients according to the changing needs of crops. Seasonal fertigation programs for greenhouse vegetable production in soil and soilless media will be described and corresponding crop performance data will be presented.

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Xiuming Hao and Athanasios P. Papadopoulos

Two long-season tomato crops (Lycopersicon esculentum Mill. cv. Trust; in 1996 and 1997) were grown in an open rockwool system (conventional culture method) and in closed rockwool culture systems with different nutrient feedings to develop a closed tomato production system with zero discharge of nutrient solutions to the environment. The tomato grown in the closed rockwool systems with a modified rockwool or nutrient film technique (NFT) feeding formula achieved similar marketable yield as the tomato grown in the conventional open rockwool system. Similarly, there were no differences in early plant growth and photosynthesis, total plant biomass and biomass partitioning, fruit yield, or fruit size and grades. The tomato plants grown in the closed rockwool systems senesced slower, as demonstrated by higher photosynthesis in old leaves, and had better root systems than the plants grown in the conventional open rockwool system. The fruit quality of tomato produced in the closed rockwool systems was better than that of tomato produced in the open rockwool system in one of two crops. These results demonstrated that the closed rockwool system with optimized nutrient feeding is an economically and environmentally sound alternative to the conventional open rockwool production method.

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Xiuming Hao and Athanasios P. Papadopoulos

Tomato (Lycopersicon esculentum Mill) `Trust' was grown on rockwool with nutrient solutions containing two levels of calcium (150 and 300 mg·L-1) in factorial combination with three levels of magnesium (20, 50, and 80 mg·L-1) in Winters 1997 and 1998, to investigate the effects of calcium and magnesium on growth, biomass partitioning, and fruit production. Plants grown at 20 mg·L-1 Mg started to show Mg deficiency symptoms (leaf chlorosis) at 8 weeks after planting. The chlorophyll content of middle and bottom leaves increased with increasing Mg concentration in the nutrient solution. At 300 mg·L-1 Ca, total fruit yield and fruit dry matter increased linearly with increasing Mg concentration; marketable fruit yield and total plant biomass showed similar response but to a lower degree. At 150 mg·L-1 Ca, total plant biomass, fruit dry matter and yield peaked at 50 mg·L-1 Mg. The biomass allocation to fruit increased while allocation to leaves decreased with increasing Mg concentration. The Mg effects on total and marketable fruit yield were mainly due to its influence on fruit yield in the late growth stage. Incidence of blossom-end rot (BER) at 150 mg·L-1 Ca increased linearly with increasing Mg concentration while it was not affected by Mg concentration at 300 mg·L-1 Ca. For a winter greenhouse tomato crop, the appropriate Ca and Mg concentrations for tomato production appear to be at 300 and 80 mg·L-1, respectively.

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Xiuming Hao and Athanasios P. Papadopoulos

Tomato (Lycopersicon esculentum Mill.) cv. Trust was grown in rockwool in summer and fall 1999 and 8 calcium/magnesium nutrient treatments, formed by two levels of calcium (Ca: 150 and 300 ppm) and four levels of magnesium (Mg: 20, 50, 80, and 110 ppm), were applied to investigate the effects on growth, fruit yield and quality. High calcium (300 ppm) increased overall fruit yield and size, reduced incidence of blossom-end rot and fruit cracking. However, high calcium also reduced the dry-matter content, soluble solid content and firmness of tomato fruit, and increased fruit russetting. Magnesium did not affect early growth or fruit production. However, 2 months after applying the treatments, the plants grown under 20 ppm Mg started to show Mg-deficient symptoms (leaf chlorosis), and Mg-deficient leaves lost more than 50% of their photosynthetic capability. The Mg concentration required for achieving high yield of firm fruit with high soluble solids and dry-matter content increased as the plant aged; i.e, 50 ppm in early stage of fruit production and 80 ppm in later stage of fruit production. At the end of experiment, the plants grown with 80 ppm of Mg also had the best root systems. Therefore, for both better yield and quality, a concentration of 300/50-80 ppm Ca/Mg may be recommended. Mg concentration may be started at 50 ppm and gradually be increased to 80 ppm in the later stage of fruit production.

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Xiuming Hao and Athanasios P. Papadopoulos

Poor tomato fruit quality in summer time (soft fruit, cracking, and russetting) is a major greenhouse production problem in North America. To improve tomato quality and yield, especially under summer conditions, four EC treatments were applied to a tomato crop grown in rockwool in summer and fall of 1999 at the Greenhouse and Processing Crops Research Centre, Harrow, Ont., Canada. The four fertigation solution EC treatments were 1) constant low EC at 2.54 mS·cm-1, 2) constant high EC at 3.82 mS·cm-1, 3) diurnal EC variation (1 to 5 mS·cm-1) with a 24-h average of 2.54 mS·cm-1 and 4) diurnal EC variation (1 to 7 mS·cm-1) with a 24-h average of 3.82 mS·cm-1. For diurnal EC variation, the plants were fed with low EC in the morning and around noon, and high EC in the afternoon and night. High EC (3.82 mS·cm-1, constant or 24-h average for diurnal variation) treatments, in comparison to the recommended EC (2.54 mS·cm-1) treatments, improved tomato fruit quality by reducing fruit cracking, and increasing percentage of grade #1 fruit, fruit firmness, soluble solid and dry-matter content. However, the constant high EC treatment resulted in smaller fruit size and lower yield. Diurnal EC variation with a high EC average (24-h average: 3.82 mS·cm-1) did not reduce fruit size and yield, and reduced fruit russetting. Therefore, a diurnal fertigation EC variation strategy-supplying low EC solution in the morning and noon and high EC solution in the afternoon and night, with an overall 24-h average of 3.82 mS·cm-1, may be used to improve tomato fruit quality.

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Xing Yuxian, Wang Xiufeng and Athanasios P. Papadopoulos

A new multilayer soilless culture system for greenhouse tomato production is described. Experiments over two spring seasons and one winter season demonstrated faster plant growth rate, higher dry matter productivity, higher fruit yield, and better fruit quality with the multilayer soilless culture system compared to the traditional soil-based culture system. The multilayer soilless culture system is suggested as a replacement of the soil-based production system to achieve significant yield improvement in greenhouse tomato production.

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Dominique-André Demers, Martine Dorais and Athanasios P. Papadopoulos

Three experiments were conducted in greenhouses 1) to determine the optimal leaf-to-fruit ratio for minimizing the incidence of russeting (miniature cuticle cracks on fruit) while optimizing fruit yield of greenhouse tomato (Lycopersicon esculentum Mill.) and 2) to investigate the effect of day/night relative humidity (RH) regimens on the development of russeting. Leaf-to-fruit ratio treatments (0.5–2.0) were achieved by varying the number of fruit (two to six fruit) per cluster and the number of leaves (two to four leaves) between clusters. In one experiment, plants were also subjected to either high day/low night or low day/high night RH regimens (low RH, 60% to 70%; high RH, 85% to 95%). Results showed that russeting of greenhouse tomato was mostly influenced by the number of fruit per cluster (total fruit load), and very little by the number of leaves between clusters. In general, decreasing the number of fruit per cluster resulted in a progressive increase in the occurrence of russeting. Furthermore, as the number of fruit per cluster decreased, the percentage of fruit with no russeting and with little russeting decreased whereas the percentage of fruit with the more severe russeting increased (except for the summer). For beefsteak cultivars Trust and Rapsodie grown under southwestern Ontario conditions, the best pruning practices for minimizing russeting and optimizing yield was to prune clusters to three fruit in early spring and late fall, to four fruit during spring and fall, and to five fruit during the summer, with three leaves between clusters all year long. In the current study, no significant effect of day/night RH regimens on fruit russeting was observed. Of the cultivars used, Rz 74/56 was less sensitive to russeting than ‘Trust’, whereas ‘Rapsodie’ was not different from the two other cultivars. However, all three cultivars had a very high incidence of russeting (>65% of fruit affected), and none should be regarded as russeting resistant. Breeding programs and genetic investigations with the objective of developing greenhouse tomato cultivars resistant to russeting are needed.

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Uttam K. Saha, Athanasios P. Papadopoulos, Xiuming Hao and Shalin Khosla

To address the concern that irrigation provides sufficient water to match the crop needs, while not impeding oxygen availability to the roots, we conducted an experiment to develop suitable irrigation schedule(s) for greenhouse tomato (Lycopersicon esculentum Mill.) on rockwool. The experimental treatments incorporated the electrical conductivity (EC) of the nutrient solution in the rockwool slab (slab-EC) along with the water content (WC) in the rockwool slab (slab-WC) as the irrigation decision-making variables. They were: slab-WC ≤ 70% or slab-EC ≥ 1.4× normal or more (T1), slab-WC ≤ 70% or slab-EC ≥ 1.7× normal or more (T2), slab-WC ≤ 80% or slab-EC ≥ 1.4× normal or more (T3), slab-WC ≤ 80% or slab-EC ≥ 1.7× normal or more (T4), and the combined weight loss (WL) 700 g or more (T5) and WL 500 g or more (T6), in which “normal” means the feed solution EC as recommended in the seasonal fertigation schedule for a spring–summer tomato crop. The data on early-season marketable yield, total seasonal marketable yield, and fruit grades indicated the superiority of treatments T1, T2, and T6 over T3, T4, and T5. Better root growth was observed with T1, T2, and T6 and this was also associated with minimized nutrient solution leaching; furthermore, these plants had an abundance of coarse and fine roots, higher photosynthesis and transpiration, higher marketable yield, and a higher water use efficiency. Our results thus established that irrigation based on either a slab water content 70% or less or a 500-g weight loss is the best strategy for rockwool-grown greenhouse tomatoes in the spring–summer season. A variation in slab-EC between 1.4 and 1.7× normal, at a slab-WC of 70% or less, would have no significant effect on root growth, water use, marketable yield, or fruit grades.

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Xiuming Hao, Guang Wen, Athanasios P. Papadopoulos and Shalin Khosla

A high-wire system, in which the plant is trained into a single stem, is gaining popularity in year-round greenhouse cucumber (Cucumis sativus) production, especially with supplemental lighting, as it allows for uniform foliar and light distribution and higher yield and quality. However, this system requires much higher plant densities than the conventional umbrella system, resulting in increased crop start-up costs. A technique for raising twin-head transplants and a twin-head “V” high-wire cucumber system were developed to address this issue. The twin-head transplants were raised by topping the seedlings after the appearance of the fourth true leaf and then two strong lateral shoots were allowed to develop and be trained into a “V” system after planting. The twin-head system achieved similar plant growth and fruit yield as the conventional single-head system on two long English seedless cucumber cultivars (Bodega and Myrthos) and two breeding lines (2005A and 24–119) tested over 2 years. The twin-head system also improved the fruit grades in ‘Bodega’ by increasing the percentage of fruit in medium size while reducing the percentage of fruit in small size. Because the twin-head system achieved the same fruit yield as the conventional single-head system while using only half the number of transplants, we can conclude that the twin-head “V” high-wire system is a more cost-effective high-wire system for year-round greenhouse cucumber production.