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Stefania De Pascale, Luisa Dalla Costa, Simona Vallone, Giancarlo Barbieri, and Albino Maggio

and, consequently, to reduce irrigation efficiency. It must be stressed that, at farm level, water is not only used to fulfil crop evapotranspiration (ET) requirements but also for other purposes, including the distribution of fertilizers and

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Gabriele Amoroso, Piero Frangi, Riccardo Piatti, Alessio Fini, and Francesco Ferrini

-Scott, 2007 ; Ferrini et al., 2009 ), but the ability of the mulches to reduce the water requirements of plants in containers is largely unknown. Some researches studied evapotranspiration (ET) rates from mulched container substrates (primarily peat based

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David R. Bryla, Thomas J. Trout, James E. Ayars, and R. Scott Johnson

A 3-year study was conducted in central California to compare the effects of furrow, microjet, surface drip, and sub surface drip irrigation on vegetative growth and early production of newly planted `Crimson Lady' peach [Prunus persica (L.) Batsch] trees. Furrow treatments were irrigated every 7, 14, or 21 days; microjet treatments were irrigated every 2-3, 7, or 14 days; and surface and subsurface drip (with one, two, or three buried laterals per row) treatments were irrigated when accumulated crop evapotranspiration reached 2.5 mm. The overall performance showed that trees irrigated by surface and subsurface drip were significantly larger, produced higher yields, and had higher water use efficiency than trees irrigated by microjets. In fact, more than twice as much water had to be applied to trees with microjets than to trees with drip systems in order to achieve the same amount of vegetative growth and yield. Yield and water use efficiency were also higher under surface and subsurface drip irrigation than under furrow irrigation, although tree size was similar among the treatments. Little difference was found between trees irrigated by surface and subsurface drip, except that trees irrigated with only one subsurface drip lateral were less vigorous, but not less productive, than trees irrigated by one surface drip lateral, or by two or three subsurface drip laterals. Within furrow and microjet treatments, irrigation frequency had little effect on tree development and performance with the exception that furrow irrigation every 3 weeks produced smaller trees than furrow irrigation every 1 or 2 weeks.

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Nicholaus D. VanWoert, D. Bradley Rowe, Jeffrey A. Andresen, Clayton L. Rugh, and Lan Xiao

Green roofs are an increasingly common, environmentally responsible building practice in the United States and abroad. They represent a new and growing market for the horticulture field, but require vegetation tolerant of harsh environmental conditions. Historically, Sedum species have been the most commonly used plants because, with proper species selection, they are tolerant of extreme temperatures, high winds, low fertility, and a limited water supply. A greenhouse study was conducted to determine how water availability influences growth and survival of a mixture of Sedum spp. on a green roof drainage system. Results indicate that substrate volumetric moisture content can be reduced to 0 m3·m–3 within 1 day after watering depending on substrate depth and composition. Deeper substrates provided additional growth with sufficient water, but also required additional irrigation because of the higher evapotranspiration rates resulting from the greater biomass. Over the 88 day study, water was required at least once every 14 days to support growth in green roof substrates with a 2-cm media depth. However, substrates with a 6-cm media depth could do so with a watering only once every 28 days. Although vegetation was still viable after 88 days of drought, water should be applied at least once every 28 days for typical green roof substrates and more frequently for shallower substrates to sustain growth. The ability of Sedum to withstand extended drought conditions makes it ideal for shallow green roof systems.

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Eric T. Stafne, John R. Clark, and Curt R. Rom

Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35 °C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37 °C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30 °C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35 °C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35 °C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35 °C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35 °C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35 °C.

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C.A. Brown, D.A. Devitt, and R.L. Morris

Research was conducted to assess the response of tall fescue (Festuca arundinacea Schreb.) to water deficit conditions. Different leaching fractions (LF = drainage volume/irrigation volume) and irrigation frequencies (IF) were imposed over a 119-day summer period in Las Vegas, Nevada, followed by a 71-day recovery period. Plots of tall fescue contained 120 cm deep × 51 cm diameter draining lysimeters. Irrigations were based on an evapotranspiration (ET) feedback system to establish LFs of +0.15, 0.00, -0.15, -0.25, and -0.40. Plots were irrigated on a daily or twice per week schedule. N was applied to subplots at a rate of 0, 12.2, or 24.4 kg·ha-1 per month. As LF decreased, relative soil water in storage declined in a linear fashion (r 2 = 0.97, P = 0.001). Storage depletions for the four lowest LFs at the end of 119 days of imposed water deficits were about 15%, 40%, 60%, and 70% compared to the +0.15 LF treatment. Canopy temperature, soil matric potential (Ψm), leaf xylem water potential (ΨLX), leaf stomatal conductance (gs), clipping yield, color and cover ratings all statistically separated (P < 0.05) based on LF but not on IF. However, irrigation amount (I), ET, tissue moisture content and total Kjeldahl N (TKN) separated based on LF and IF with a significant LF by IF interaction for I (P < 0.05) and TKN (P < 0.001). An irrigation savings of 60.4 cm was realized during the 119-day water deficit period at the -0.40 LF. However, at the lower LFs, plant stress increased (all parameters) with color ratings declining below an acceptable value of 8.0. An Irrigation/Potential ET (I/ETo) threshold of 0.80 was determined for both color and cover. After a 71-day recovery period both color and cover returned to pre experimental values at the two higher N rates. Results of this experiment indicate that implementing a twice weekly irrigation strategy at a -0.15 LF on tall fescue during summer months in an arid environment would lead to savings of 37.5 cm of water while still maintaining acceptable color and cover ratings.

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Andrea L. Medina-Holguín, Sandra Micheletto, F. Omar Holguín, Jaime Rodriguez, Mary A. O'Connell, and Charles Martin

initiated when crowns broke dormancy and leaves were fully emerged; drip irrigation [25%, 50%, and 100% of daily pan evapotranspiration rate (PET)], and nitrogen (N) fertilizer [0, 4.6, and 9.2 kg/ha as Ca(NO 3 ) 2 ]. Water volume applied to each treatment

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Robert H. Stamps and Heidi M. Savage

using graphics software (SigmaPlot version 11; Systat Software, San Jose, CA). Results and discussion Evapotranspiration. Cumulative water loss before any plants were visibly wilted was linear ( r 2 values from 0.9999 to 0.9964) and greater ( P ≤ 0

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Doyle A. Smittle, W. Lamar Dickens, James R. Stansell, and Eric Simonne

Turnip (Brassica rapa L.) and mustard (Brassica juncea L.) were grown in drainage lysimeters under controlled soil water regimes during 2 years. Irrigation regimes consisted of water applications when the soil water tension at a 10-cm depth exceeded 25,50, or 75 kPa throughout growth of the two crops on two soil types during spring and fall production seasons. Leaf yield and water use were highest when irrigation was applied at 25 kPa soil water tension. Regression equations are presented to describe the relationships of daily pan evaporation and water use to plant age, and to compute daily evapotranspiration: pan evaporation ratios (crop factors) during spring and fall production seasons.

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Doyle A. Smittle, W. Lamar Dickens, and James R. Stansell

Cabbage (Brassica oleracea L.) was grown in drainage lysimeters under controlled soil water regimes during 3 years. Three irrigation regimes were imposed on cabbage grown on two soil types during the spring and fall growing seasons. Irrigation regimes consisted of applying water when the soil water tension at 10 cm exceeded 25, 50, or 75 kPa during crop growth. Yields and water use were highest when irrigation was applied at 25 kPa soil water tension. Regression equations are presented to describe the relationships of water use to plant age and to compute the ratios of daily evapotranspiration to pan evaporation (crop factors) for cabbage grown under the three irrigation regimes.