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M.A. Kasrawi, N. Khraishi and Y. Tabaza

A greenhouse experiment was conducted over two growing seasons to study the physical and mechanical properties of a recycled multilayer plastic cover and its effect on the production of greenhouse-grown tomatoes. Two experimental greenhouses were constructed, one covered with recycled multilayer film and the other with conventional virgin monolayer film. The air temperature under both covers was similar; the soil temperature in the recycled multilayer house was a few degrees lower in the afternoon hours to midnight than in the virgin monolayer house. The recycled multilayer film retained its strength and elasticity over a useful service life of 7 months (one growing season), after which severe degradation occurred as manifested by a 50% loss of elongation at break. During the useful lifetime of the film, haziness, light scattering, and light transmission of the recycled film was similar to the conventional film. The thermal analysis of the recycled film revealed a low stability against thermo-oxidative degradation and the infrared analysis indicated the presence of a measurable amount of degradation products, mainly carbonyl groups, in the recycled film in comparison with conventional film. During the useful lifetime of recycled film, yield components of the tomato crop were identical to the conventional film in both growing seasons. In conclusion, waste plastic recycling offers an attractive solution to nuisance environmental problems. However, the useful lifetime of recycled films needs to be improved.

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M.P.N. Gent and Y.-Z. Ma

Does heating roots only in the day improve growth and nutrient status of seedlings grown under a day-to-night difference (DIF) in air temperature? To answer this question, tomato seedlings (Lycopersicon esculentum Mill) were grown in early March or April in greenhouses heated to give either a 14 °C DIF or a 5 °C DIF with a 18 °C mean. The roots were in peat-vermiculite medium that was unheated or heated to 21 °C, constantly or only in the day, or only in the night. Growth was faster and there were higher concentrations of elements in leaves under 5 °C compared to 14 °C air DIF. Any root-zone heating increased growth and nutrition compared to no heating. Under both air conditions, the trend in root temperature treatments was constant > day > night. In general, there was no benefit of heating the roots only in the day, compared to constant heating of the root zone, even with a large diurnal variation in temperature of the shoot. The only nutrient to respond differently to root heating under 5 °C compared to 14 °C air DIF was nitrate in leaves. Under a 14 °C air DIF, heating roots in the day resulted in the highest nitrate concentration, whereas constant root heating was optimal under a 5 °C DIF. Research supported in part by grant 93-37100-9101 from NRI Competitive grants program/USDA.

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Yong-Zhan Ma and Martin P.N. Gent

Tomato (Lycopersicon esculentum Mill) seedlings were grown with air temperature of 28°C light/12°C dark (12/12 hours), and either a constant, 20°C, root-zone temperature (RZT), or in-phase with air temperature, 28°C in the light and 12°C in the dark, or out-of-phase, 12°C in the light and 28°C in the dark. These treatments were applied from 17 to 25 days after germination, with 200 m \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document} in flowing nutrient solution. The relative growth rate of leaves was the greatest with constant RZT, 0.33/d, and least with out-of-phase RZT, 0.29/d. The concentration of free amino acid and protein in leaves was least for out-of-phase RZT. The \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document} concentration in leaves was the highest in the dark, intermediate in the middle of the light period, and the lowest at the end of the light period. In roots, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document} concentration showed a similar trend. This variation was greatest when RZT was varied out of phase, and least with constant RZT. At the end of the light period, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document} concentration in roots was 246, 180, and 162 μmol·g–1 dry weight for constant, in phase, and out of phase RZT, respectively. In the light, leaves of seedlings grown with out-of-phase RZT had 5 mmol·g–1 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document}, compared to 16 mmol·g–1 with in-phase RZT Availability of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{-}^{3}\) \end{document} in the light may be the factor limiting plant growth with out-of-phase RZT. This research was supported in part by grant number 93-37100-9101 from the National Research Initiative Competitive Grants Program/USDA.

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M.P.N. Gent and Y.Z. Ma

What is the effect of constant compared to intermittent heating of the shoot and root on growth, nutrient status, and yield of greenhouse tomato (Lycopersicon esculentum Mill)? Seedlings were transplanted early, on 4 Mar. 1994 and 1 Mar. 1995, or late, on 25 Mar. 1994 and 31 Mar. 1995, into troughs of peat-lite mix. The troughs were heated to 21C by buried tubing, either constantly, or for 12 h during the day or the night, or they were not heated. The greenhouses had either 14/14C or 22/6C day/night minimum air temperatures. After 2 weeks, early transplants had the greatest leaf weight with constant root heat and least with no heat. Root weight was greater for 14/14C than 22/6C air heat. With 14/14C air heat, only the no-root heat reduced leaf weight, whereas with 22/6C air heat, root heat ranking was constant > day > night ≈no heat. With late transplants, only the no heat reduced leaf weight. Most nutrient concentrations were less in late than in early transplants. Number of fruit, and number and weight of marketable fruit produced by 1 July from early transplants was affected by root heat; the ranking was constant heat > day > night > no heat. The 22/6C air heat increased marketable yield because of fewer small, irregular and blossom end rot fruit. Root heat had no effect on yield of late transplants.

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Yong-Zhan Ma and Martin P.N. Gent

How are C and N metabolites affected by a root-zone temperature (RZT) in phase or out of phase with the photoperiod? Tomato (Lycopersicon esculentum Mill.) was grown with an air temperature of 20C, and RZT that was in phase with a 12-h photoperiod, 28C in the light and 12C in the dark, or out of phase, 12C in the light and 28C in the dark. Seedlings were grown in flowing solution containing 200 μm NO3 and excess amount of other mineral elements. The flow rate increased with plant size. After 8 days, plants were harvested at the end of the day and at the end of the night. The relative growth rate (day–1) was slightly greater for in-phase (0.19) than out-of-phase RZT (0.17) and less than that at a constant air and RZT of 24C (0.22). RZT affected N accumulation and partitioning of C and N metabolites. Cool roots contained more NO3 and free sugars than warm roots. Leaves had less NO3 in the light than in the dark, and NO3 in leaves of plants with an out-of-phase RZT was depleted in the light. Concentration of free amino acids and protein was greater and the amount of starch was less in leaves of plants with in-phase RZT.

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M.P.N. Gent and Y.-Z. Ma

Is intermittent heating of the root zone more beneficial than constant heating for production of greenhouse tomato (Lycopersicon esculentum Mill), with diurnal variation of air temperature (DIF)? Yields were compared with 14°C day/14°C night or 22°C day/6°C night minimum air temperatures, resulting in 5 and 14°C DIF. The root zone was unheated or was heated to 20°C constantly or for 6 hours in the day, or 6 hours in the night. The greenhouse tomato cultivars Buffalo and Caruso were transplanted in early and late March in 1994 and 1995. Averaged over both years and cultivars, the yield from early March planting with 14°C DIF was greater than with 5°C DIF, 6.6 and 6.1 kg/plant, respectively, due to an increase in weight per fruit and to earlier ripening. Root zone heat increased yield compared to no heat, due to a greater number of fruit. With 5°C DIF, yields with constant and intermittent root zone heat were similar. The yields were 5.4, 6.4, 6.2, and 6.2 kg/plant with none, day, night and constant heat, respectively. With 14°C DIF, there were larger differences in yield, 5.7, 7.0, 6.6, and 7.1 kg/plant with none, day, night and constant root zone heat, respectively. However, interactions between air and root heat regimes were not statistically significant. The yield from late March planting was greater with 14°C than with 5°C DIF, but root zone heat had no effect. Research supported in part by grant 93-37100-9101 from NRI Competitive grants program/USDA.

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Martin P.N. Gent and Yong-Zhan Ma

What is the effect of constant compared to diurnal heating of the shoot and root on growth and yield of greenhouse tomato (Lycopersicon esculentum L.)? Seedlings were transplanted on 4 or 25 Mar. 1994 into troughs that were not heated or heated to 21C by buried tubing, either constantly or for 12 h during the day or the night. The greenhouses had either 14/14C or 26/6C day/night minimum air temperatures. After 2 weeks, leaves of the 4 Mar. transplants weighed most with constant root heat and least with no heat. Roots weighed more with 14/14C than 26/6C air heat. With 14/14C air heat, only no root heat reduced leaf weight, whereas with 26/6C air heat, leaf weight was in the order: constant > day > night - no heat. After 2 weeks, leaves of the 25 Mar. transplants weighed least with no heat, and other treatments did not differ. Root heating affected yield. By 1 July, the number of fruit and the number and weight of marketable fruit produced from 4 Mar. transplants was in the order: constant heat > day > night > no heat. The 22/6C air heat increased marketable yield because fewer fruit were small, irregular, or had blossom-end rot. Root heat had no effect on yield of 25 Mar. transplants.

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Yona-Zhan Ma and Martin P.N. Gent

Nitrate (NO3) was supplied at 100, 200, 400, and 800 μm in nutrient solution to 3-week-old tomato seedlings grown hydroponicly, and day and night concentrations of N and C metabolites were measured. Tissue [NO,] at the end of the night was greater than at the end of the day, especially for leaves. Leaf tissue [NO3] was about 350 μmol·g-1 dry weight at night, 3 times as high as that during the day. Generally, root and stem tissue [NO,] was similar and higher than that of leaves and increased as medium [NO,] increased. The difference was greater at night than during the day. During the day, total free amino acid concentration was the greatest for roots and the least for stem. Generally, root tissue had higher total free sugar concentration than leaf and stem tissues during the day. Fructose concentration was lower at night than during the day for all parts of the plants, especially for roots. At night, NO3 accumulated in plant tissues, especially in leaves, and was not incorporated into amino acids, perhaps due to the lack of energy and reductant.

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J.E. Motes, B. Bostian and N. Maness

The objective of this study was to evaluate the possible causes for greater pungency in pepper (Capsicum annuum) pods of two chile selections when produced at eastern and western Oklahoma locations. Pungency tests over several years have demonstrated that peppers grown in western Oklahoma consistently produce pods with ≈25% greater pungency than peppers grown in eastern Oklahoma. Data from Oklahoma Mesonet stations located near each production location indicated the western Oklahoma location had higher temperatures and wind speed but lower relative humidity than the eastern Oklahoma location during pod development. Mature dry pods were dissected into cap and stem, seeds, and pod wall. Comparisons of pod component differences between the locations showed pods were similar in dry weight; however, western Oklahoma produced more cap and stem in both selections, and in one selection produced more pod wall but less seed. Pungency was 24% and 28% greater in the two selections when grown in western Oklahoma. More pod wall and less seed could account for some of the pungency increase in only one of the selections. The more stressful production environment in western Oklahoma appears to be the major factor in pungency differences between the locations.

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M.P.N. Gent and Y.-Z. Ma

What is the effect of constant compared to intermittent heating of the shoot and root on growth, nutrient status, and yield of greenhouse tomato (Lycopersicon esculentum Mill)? Seedlings were transplanted on 4 Mar. or 25 Mar. 1994 into troughs heated to 21C by buried tubing, either constantly, or for 12 h during the day or the night, or they were not heated. The greenhouses had either 14/14C or 22/6C day/night minimum air temperatures. After 2 weeks, the 4 Mar. transplants had the greatest leaf weight with constant root heat and least with no heat. Root weight was greater for 14/14 than 22/6 air heat. With 14/14 air heat, only the no root heat reduced leaf weight, whereas with 22/6 air heat, root heat affected leaf weight; the ranking was constant > day > night ≈ no heat. After 2 weeks, the 25 Mar. transplants had least leaf weight with no heat, and other treatments did not differ. Most nutrient concentrations were less in the 25 Mar. compared to the 4 Mar. transplants. The number of fruit, and the number and weight of marketable fruit produced by I July from 4 Mar. transplants was affected by root heat; the ranking was constant heat > day > night > no heat. The 22/6 air heat increased marketable yield, because of fewer small, irregular, and blossom end rot fruit. Root heat had no effect on yield of 25 Mar. transplants. Research supported in part by grant 93-37100-9101 from NRI Competitive grants program/USDA.