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Hans-Peter Kläring and Angela Schmidt

( Marcelis and Baan Hofman-Eijer, 1993 ). Nevertheless, reports show that cucumber can be grown successfully at low night temperatures of 11–14 °C ( Heißner and Drews, 1986 ). One reason for this phenomenon could be that diurnal temperature variations have an

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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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Hans Christian Wien

Simple unheated greenhouses covered with clear polyethylene, also known as high tunnels, in which plants are typically grown in the ground have become popular for extending the growing season for high-value horticultural crops. Although they are used principally to produce annual crops such as vegetables and cut flowers, increasing interest has focused on their use for perennial crops such as raspberries, blackberries, and ornamentals. Studies of temperature variation within the tunnel during the growing season have emphasized the rapid rise in air day temperature above ambient during the day and an equally rapid decrease at night. Spatial variation in temperature within the tunnel were much less marked, however, with air temperatures at the edge of a 10-m wide tunnel only ≈2 °C lower than in the center. For perennial crops, tunnel conditions during the off-season are also an important factor. In winter, air temperatures in the tunnel during sunny days rose above freezing even when ambient air temperatures stayed below freezing. Soil temperatures during the day and night fluctuated much less both inside and outside the tunnel and were significantly higher in the tunnel. Studies with nursery plants overwintered in similar structures indicate that spatial variation is again dwarfed by the overall air temperature fluctuation in these structures.

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Helen H. Taylor, Robert L. Mikkelsen, and Stuart L. Warren

The N release patterns of composted turkey litter, composted yard waste, and composted municipal waste amended pine bark substrates were measured under simulated diurnal temperature variations [25C, 45C, and 45/25C (14/10 h)] found in container substrates. Temperature regime, compost, and the interaction between temperature and compost affected the NH4 and NO3 availability and the total N released from the composted waste products over the 16-week experiment. Within each temperature regime, the composted turkey litter released greater amounts of NH4 and more total inorganic N than the municipal and yard wastes. The turkey litter yielded the highest NO3 concentrations at 25C, while the municipal waste produced the highest NO3 concentrations at the 45C and the 45/25C temperatures. Temperatures higher than 25C inhibited nitrification in the turkey litter-amended substrates; however, the 45C and the 45/25C treatments resulted in greater total N mineralization than the 25C treatment.

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Britney Hunter, Dan Drost, Brent Black, and Ruby Ward

-elevation climates like Utah, daytime temperatures spring can be quite warm (10 to 20 °C) even when nighttime temperatures are below freezing ( Moller and Gillies, 2008 ). These extreme diurnal temperature variations can limit the length of the growing season for

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Carlos De la Cuadra, Alexis K. Vidal, and Leví M. Mansur

average temperatures vary between 13.0 and 20.5 °C with a diurnal temperature variation of 7.5 °C; the monthly high and low temperatures are 24.5 and 9.8 °C, that occur in January and July, respectively ( Fig. 3 ). The average of clear days per year is

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Sezgin Uzun

growth of tomato plants. II. The effects of irradiance and temperature Plant Physiol. 81 1075 1079 Gent, M.P.N. 1988 Effect of diurnal temperature variation on early yield and fruit size of greenhouse tomato Appl. Agr

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Johshin Tsuruyama and Toshio Shibuya

to 350 µmol·m −2 ·s −1 with the LEDs) probably lowered the photosynthetic light-use efficiency. Moreover, the diurnal temperature variation may have limited seedling growth in the greenhouse because the daily maximum temperatures [>30 °C ( Fig. 2

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Hanna Y. Hanna and Kenneth D. Henderson

.A. Baird, C.D. Chapman, F.A. Watson, C.A. 1997 Comparison of energy needed to heat greenhouses and insulated frame buildings used in aquaculture Univ. Florida Coop. Ext. Serv. Circ 1198 Gent, M.P.N. Ma, Y.-Z. 1998 Diurnal temperature variation of the root

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Rolston St. Hilaire, Theodore W. Sammis, and John G. Mexal

hoop houses were seeded on 4 Oct. 2006 [(°F − 32) ÷ 1.8 = °C]. Hoop houses were built by students in the Introduction to Horticulture class (HORT 100G) at New Mexico State University. Diurnal temperature variation averaged 32 °F during fall and winter