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D. Michael Glenn

Water use efficiency (WUE) or transpiration efficiency, the ratio of carbon assimilation to transpiration (E), is a conservative characteristic of species and cultivars ( Jones, 1992 , 2004 ). The conservative nature is due to genetic and

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Osama Mohawesh, Ammar Albalasmeh, Sanjit Deb, Sukhbir Singh, Catherine Simpson, Nour AlKafaween, and Atif Mahadeen

nets on enhanced soil water content or soil water potential as well as water use efficiency have been reported by different studies. For instance, Möller and Assouline (2007 ) concluded that 30% black shading net reduced solar radiation and increased

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John Erwin, Tanveer Hussein, and David J. Baumler

5 min (RH; %) and water use efficiency (WUE; WUE = P n /E) among 33 outdoor-grown pepper varieties that vary in indigenous habitat and species. Indigenous habitats used for analysis are shown as superscript numbers after the variety name ( 1 desert

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Lloyd L. Nackley, Jig Han Jeong, Lorence R. Oki, and Soo-Hyung Kim

nitrogen (N) treatments. Leaf gas-exchange parameters include net CO 2 assimilation rates ( A ), instantaneous leaf water use efficiency (WUE), Rubisco capacity ( V cmax ), and potential electron transport rate ( J max ). The V cmax was significantly

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Dalong Zhang, Yuping Liu, Yang Li, Lijie Qin, Jun Li, and Fei Xu

t 2 were 20 and 40 d after transplanting in the current study, respectively. Transpired water consumption and WUE. Whole-plant water use efficiency (WUE plant ) was calculated as the ratio of the shoot biomass to the cumulative amount of water

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Chiara Cirillo, Youssef Rouphael, Rosanna Caputo, Giampaolo Raimondi, and Stefania De Pascale

( Table 3 ). Table 3. Effects of irrigation treatments, genotypes, and shapes on number of leaves, total leaf area, number of flowers, and flower density of potted Bougainvillea plants. Water requirement and water use efficiency. Irrespective of genotype

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D. Michael Glenn, R. Scorza, and W.R. Okie

Two unpruned narrow-leaf and two unpruned standard-leaf peach [Prunus persica (L.) Batsch.] selections were evaluated for physiological components related to water use efficiency {WUE [carbon assimilation (A) per unit of transpiration (T)]}. The purpose of the study was to assess the value of narrow-leaf phenotypes to improve WUE in peach and separate the environmental component of canopy geometry from the genetic components. The narrow-leaf characteristic itself did not confer improved WUE. The interception of light was a key determinant of WUE in these genotypes. Internal shading of the tree by excessive leaf area reduced daily WUE measured in gas exchange studies. Canopies that intercepted more than 75% of the photosynthetically active radiation (PAR) had reduced daily WUE. Dormant season pruning of the four genotypes lowered isotopic carbon discrimination and therefore increased seasonal WUE compared to unpruned trees. None of the genotypes had a significant correlation of seasonal WUE with leaf and fruit weight. Analysis of covariance indicated that `Bounty' and both narrow-leaf genotypes had greater leaf and fruit weight than `Redhaven' for a given level of PAR interception. `Bounty' had the least internal canopy shading of the four genotypes. Genetic differences in peach growth types can be selected for factors increasing WUE as well as increased productivity. Future work in peach breeding to improve WUE and productivity must take into consideration light interception, productivity, and WUE in an integrated manner to make real progress in the efficient use of water and light in the orchard environment.

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D.C. Fare, C.H. Gilliam, and G.J. Keever

Improved water use efficiency exists for plants grown in modified containers to minimize leaching and reduce irrigation frequency which subsequently reduces NO3-N leachate. Salvia splendens `Bonfire' and Impatiens wallerana `Pink' (super elfin hybrid) were potted in ProMix BX medium (Premier Brands, Inc., Stamford, CT) into nine container styles with modified drainage holes to determine leachate volume and quantify NO3-N leached. Three styles had four drainage holes on the container side with hole diameters of 0.5, 1.0, and 1.9 cm, respectively; three styles had four drainage holes on the container side and one drainage hole in the bottom center with hole diameters of 0.5, 1.0, and 1.9 cm, respectively; and three styles had one drainage hole in the bottom center with hole diameters of 0.5, 1.6, and 1.9 cm, respectively. Plants were hand watered when an individual container's medium reached 80% of container capacity. Leachate volume, irrigation frequency, and leachate NO3-N was reduced as drainage size hole decreased in size and number. Plant quality was similar among container modifications.

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R. Louis Baumhardt, W. N. Lipe, David Rayburn, and C. W. Wendt

Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).

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R. Louis Baumhardt, W. N. Lipe, David Rayburn, and C. W. Wendt

Mild temperatures during late winter have caused early budbreak in grapes which resulted in freeze injury and significant crop losses in 1980 and 1988. Evaporative cooling of grapevines with microsprinklers when the air temperature exceeded 10 °C (50 °F) used 100 liters/min/hectare of treated grapes (11 gallons/min/acre) and delayed budbreak for a period of 7 to 10 days. Methods of reducing the amount of water used while not reducing the cooling were evaluated. The average hourly difference between wet and dry bud temperatures, measured with thermocouples, were summed during the system operation time and compared as a function of air temperature, wind speed, global radiation, and relative humidity limits. Limiting the cooling system operation time as a function of air temperature, wind speed, or global radiation reduced cooling efficiency by approximately a one to one ratio. Limiting system operation to humidities less than 60% reduced the amount of water used by 33%, with only a 9% reduction in cooling efficiency. By changing the wetting interval employed in this research from 25 seconds every three minutes to 25 seconds every four minutes, total water conservation would increase to 50% with insignificant changes in cooling efficiencies. These system modifications would reduce water application requirements to 50 liters/min/hectare of grapes (5.5 gallons/minute/acre).