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Xu Zhang, Na Ta, Wei-ye Tian, Li-jun Gao, and Wei Jiao

Soil temperature affects the growth and development of crops ( Sun, 2005 ). Studies have shown that a 1 °C difference in soil temperature will seriously affect crop growth and development ( Sarkar et al., 2007 ; Sypka et al., 2016 ). Soil

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Kayla Snyder, Amanda Grant, Christopher Murray, and Bryon Wolff

-Pérez and Batal, 2002 ; Greer and Dole, 2003 ; Lamont, 1993 ) on soil temperature ( Chakraborty et al., 2008 ; Díaz-Pérez, 2009 , 2010 ; Díaz-Pérez et al., 2005 ; Lamont, 2005 ), moisture ( Chakraborty et al., 2008 ; Greer and Dole, 2003 ; Ramalan

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J. Scott Ebdon and Michelle DaCosta

temperatures (≈10 °C) typical of early spring plantings in the northern United States reduce seed germination and establishment vigor of cool-season grasses when compared with more favorable soil temperatures of 20 to 30 °C ( He et al., 2013 ; Liu et al., 2001

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Theo J. Blom and Brian D. Piott

The effect of constant 16C and noncontrolled soil temperature on flowering of four Alstroemeria cultivars grown in a greenhouse was studied over 3 years. Soil temperature regime did not influence either the start or cessation of flowering. During spring/summer, production was 15% lower under constant soil temperature, irrespective of cultivar. During fall/winter, the effect of constant soil temperature was cultivar-dependent; yield of `Red Sunset' was increased by 150%, while that for `Rio' decreased by 2270 relative to the noncontrolled. Annual production was not affected, but the ratio between the production of spring/summer and fail/winter decreased from 3.1 to 2.2 for noncontrolled and constant soil temperature, respectively.

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Rahmatallah Gheshm and Rebecca Nelson Brown

between the air and the rhizosphere ( Rosenberg et al., 1983 ; Tarara, 2000 ) By modifying the radiation budget, plastic mulches directly affect the rhizosphere microclimate. The soil temperature under plastic mulch depends on the optical properties of

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E.W. Pavel and E. Fereres

Responses to low soil temperatures at winter days of high evaporative demand were studied in 20-year-old (fi eld) and 1-year-old potted (controlled conditions) olive (Olea europaea L. cv. Picual) trees in 1996 and 1997. Low soil temperatures apparently affected tree water status as evidenced by low water potentials and stomatal conductance. Low night (2 and 5°C) but ambient day (above 10°C) temperatures did not affect stomatal conductance (gl), leaf (ψl), and xylem (ψx) water potentials of potted olive trees. Tree ψl and ψx decreased when exposed to low night and day temperatures (8°C), but gl was not affected. Water potential of those trees recovered very rapidly when the soil temperature was raised above 10°C at midday. When the trees were exposed to soil temperatures below 8°C for 3 days, ψl, ψx, and gl immediately decreased. After the first day, gl and ψx started to recover while gl was maintained at low levels, thus allowing for tree rehydration. Root hydraulic resistance (rroot)—a major part of whole plant resistance—increased immediately in response to soil temperatures below 10°C relative to that of control trees. The relationship between ψx and rroot indicated that the root system apparently plays a mayor role in the control of tree water status in response to low soil temperatures. During the winter months, olive tree water uptake seems to be primarily limited by low soil temperatures, even though soil water content is normally adequate due to high seasonal rainfall.

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B.R. Gardner and C.A. Sanchez

Lettuce is planted in the southwestern U.S. desert from September through December and harvested from November through April each year. During this period mean soil temperatures range from 7 to 30C. Lettuce produced on desert soils shows a large yield response to P. Soil solution P is replenished by desorption from the labile soil P fraction and this process is temperature sensitive. A field study was conducted over 6 years to evaluate the response of lettuce to soil solution P levels under different ambient soil temperature regimes. The soil temperatures under which lettuce was grown were varied each year by altering planting dates. Soil solution P levels were established and maintained each season using P sorption isotherm methodology. Lettuce responded to P in all experiments. Phosphorus levels required for maximum yield varied with each experiment. Soil P levels required for optimal yield were best correlated to mean soil temperatures during the last 20 days before harvest. Lettuce accumulates over 70% of its P during the heading stage of development and it is likely that during this period of rapid growth and nutrient uptake, solution P becomes limiting when soil temperatures are cool.

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Timothy K. Broschat

Royal palms [Roystonea regia (HBK.) O.F. Cook], coconut palms (Cocos nucifera L. `Malayan Dwarf'), queen palms [Syagrus romanzoffiana (Chamisso) Glassman], and pygmy date palms (Phoenix roebelenii O'Brien) were grown in a rhizotron to determine the patterns of root and shoot growth over a 2-year period. Roots and shoots of all four species of palms grew throughout the year, but both root and shoot growth rates were positively correlated with air and soil temperature for all but the pygmy date palms. Growth of primary roots in all four species was finite for these juvenile palms and lasted for only 5 weeks in royal palms, but ≈7 weeks in the other three species. Elongation of secondary roots lasted for only 9 weeks for coconut palms and less than half of that time for the other three species. Primary root growth rate varied from 16 mm·week-1 for coconut and pygmy date palms to 31 mm·week-1 for royal palms, while secondary root growth rates were close to 10 mm·week-1 for all species. About 25% of the total number of primary roots in these palms grew in contact with the rhizotron window, allowing the prediction of the total root number and length from the sample of roots visible in the rhizotron. Results indicated that there is no obvious season when palms should not be transplanted in southern Florida because of root inactivity.

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Barbara J. Daniels-Lake, Robert K. Prange, Sonia O. Gaul, Kenneth B. McRae, Roberto de Antueno, and David McLachlan

with unusually hot soil temperatures, in the production of TCA-based “musty” OFO in the 2001 crop. This study has identified influences of high soil temperature and pesticides other than γ-CHC on the release of TCA from soil, and the presence of TCA in

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John R. Teasdale and Aref A. Abdul-Baki

Temperature and root length at selected locations within a raised bed under black polyethylene (BP), hairy vetch (Vicia villosa Roth) residue (HV), or bare soil (BS) were measured and correlated with tomato (Lycopersicon esculentum Mill.) growth. Early in the season, before the tomato leaf canopy closed, soil temperature was influenced more by vertical depth in the bed than by horizontal location across the bed. Maximum soil temperatures under BP averaged 5.7 and 3.4C greater than those under HV at 5- and 15-cm depths, respectively. More hours at temperatures >20C during the first 4 weeks probably accounted for greater early root and shoot growth and greater early yield of tomatoes grown in BP rater than in HV or BS. After canopy closure, soil temperatures under tomato foliage were reduced compared to those on the outer edge of the beds. Most tomato roots were in areas of the bed covered by the tomato canopy where temperatures in all treatments remained in the optimum 20 to 30C range almost continuously. Soil temperature, therefore, did not explain why total yield was higher in the HV than the BP or BS treatments.