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Yiwei Jiang, Huifen Liu, and Van Cline

( Jiang and Carrow, 2007 ). Responses of turfgrass to water deficit conditions can also be assessed by leaf or canopy temperature. Leaf temperature will be greater than ambient temperature when grasses are under drought stress as a result of reduced

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Bernadine C. Strik, Amanda J. Davis, David R. Bryla, and Scott T. Orr

the field and to facilitate data collection on soil and canopy temperature with five replicates. Each plot included a row of nine plants spaced 0.9 m apart and was separated from adjacent plots in the row by 3 m. Rows were spaced 3 m apart. Guard rows

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Jeffrey C. Stark, Joseph J. Pavek, and Ian R. McCann

Field studies were conducted in 1986 and 1987 to evaluate the potential of using canopy temperature measurements to evaluate the relative drought tolerance of potato genotypes. In both years, 14 potato genotypes representing a relatively wide range of Solarium tuberosum L. germplasm were grown under well-watered [irrigation ≈100% potential evapotranspiration (ET) and stressed (irrigation ≈40% to 50% potential ET) coditions. Irrigation differences were imposed with a line source irrigation system. Canopy temperatures of the 14 genotypes were measured between 0900 and 1430 hr on 7 clear days during tuber bulking. A general linear relationship between canopy minus air temperature (ΔT) and air vapor pressure deficit (VPD) was determined for each year by regressing all ΔT data onto corresponding VPD values. The relative sensitivity of each genotype to changes in VPD was determined by regressing observed ΔT values onto the estimated ΔT from the general equation for that year. Genotypes with higher than average temperatures under well-watered conditions were generally less sensitive to changes in VPD than those with lower than average temperatures. Warmer genotypes under well-watered conditions were also generally less susceptible to drought than cooler genotypes. Thus, ΔT measurements from well-watered plots can be effectively used to assess the relative drought tolerance of potato genotypes.

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Gerald Henry, Rebecca Grubbs, Chase Straw, Kevin Tucker, and Jared Hoyle

best) from the reflectance readings. An average of three readings were obtained per DWT level per mowing treatment in each tank. Canopy temperature (°C) was recorded using an Oakton TempTester IR thermometer (OAKTON Instruments, Vernon Hills, IL). An

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D.M. Glen

This work focuses on recent developments and examples of irrigation scheduling that concern where in the root system and when in the plant's phenology water should be applied. Information is provided on using and measuring soil variability to help schedule irrigation. An irrigation model is described that emphasizes the soil water-holding capacity and root distribution in designing irrigation systems and scheduling water application. Recent research is reviewed on the subject of fruit crops that can tolerate severe water stress during specific growth periods of the fruit. Finally, a method of using infrared thermometers and canopy temperature data in cloudy, humid regions is presented that has the potential to extend the use of this technology.

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M.J. Hattendorf and J.R. Davenport

Cranberry (Vaccinium macrocarpon Ait.) evapotranspiration (ET) has not been documented. Micrometeorological techniques based on canopy temperature minus air temperature were used to estimate ET on `Stevens' and `Crowley' cranberry at Long Beach (lat. ≈46°20′N, long. 124°W) and Grayland (lat. ≈46°47′N, long. 124°W), Wash., in 1991 and 1992, respectively. Cranberry ET was 55% of Priestley–Taylor reference ET and ranged from <0.5 to >4 mm·d–1. The Priestley–Taylor reference ET was a very good predictor of cranberry ET (r 2 = 0.795). Running 7-day cumulative ET ranged from 7 to 17 mm·week–1.

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Daniel I. Leskovar and Giovanni Piccinni

Restrictions placed on water usage for farmers have prompted the development of irrigation management projects aiming at water savings of economically important crops. The objective of this work was to determine yield, water use efficiency, and leaf quality responses to deficit irrigation rates of processing spinach (Spinacea oleracea L.) cultivars. Three irrigation treatments were imposed with a center pivot system, 100%, 75%, and 50% crop evapotranspiration rates (ETc). Commercial cultivars used were `DMC 09', `ASR 157', and `ACX 3665'. Leaf quality was significantly affected by deficit irrigation rate and cultivar. Leaf yellowness was highest at 50% ETc, and was more evident for `ACX 3665'. The percent excess stem (>10 cm) was higher at 100% ETc. This response was greater in `ACX 3665' than in `ASR 157' and `DMC 09'. Marketable yields were significantly higher for `ASR 157' at either 100% or 75% ETc rates, compared to `DMC 09' and `ACX 3665'. High water use efficiency was also measured at 75% ETc for `ASR 157'. Minimum canopy temperature differences were detected among the irrigation treatments. This work demonstrated that it is possible to reach a 25% water savings in one season, without reducing yields when using vigorous cultivars.

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Yiwei Jiang, Robert N. Carrow, and Ronny R. Duncan

Traffic stresses often cause a decline in turfgrass quality. Analysis of spectral reflectance is valuable for assessing turfgrass canopy status. The objectives of this study were to determine correlations of narrow band canopy reflectance and selected reflectance indices with canopy temperature and turf quality for seashore paspalum exposed to wear and wear plus soil compaction traffic stresses, and to evaluate the effects of the first derivative of reflectance and degree of data smoothing (spectral manipulations) on such correlations. `Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) was established on a simulated sports field during 1999 and used for this study. Compared to original reflectance, the first derivative of reflectance increased the correlation coefficient (r) of certain wavelengths with canopy temperature and turf quality under both traffic stresses. Among 217 wavelengths tested between 400 and 1100 nm, the peak correlations of the first derivative of reflectance occurred at 661 nm and 664 nm for both canopy temperature and turf quality under wear stress, respectively, while the highest correlations were found at 667 nm and 820 to 869 nm for both variables under wear plus soil compaction. Collectively, the first derivative of reflectance at 667 nm was the optimum position to determine correlation with canopy temperature (r > 0.62) and turf quality (r < -0.72) under both traffic stresses. All correlations were not sensitive to degrees of smoothing of reflectance from 400 to 1100 nm. A ratio of R936/R661 (IR/R, Infrared/red) and R693/759 (stress index) had the strongest correlations with canopy temperature for wear (r = -0.63) and wear plus soil compaction (r = 0.66), respectively; and a ratio of R693/R759 had the strongest correlation with turf quality for both wear (r = -0.89) and wear plus soil compaction (r = -0.82). The results suggested that the first derivative of reflectance could be used to estimate any single wavelength simultaneously correlated with multiple turf canopy variables such as turf quality and canopy temperature, and that the stress index (R693/R759) was also a good indicator of canopy stress status.

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Wei-Ling Chen and Chun-Jung Shen

PPFD (presented as μmol·m −2 ·s −1 ) and then converted to solar radiation (presented as joule·m −2 ·s −1 ) at a conversion value of 2.1. Light distribution, spectrum, and canopy temperature. The transmitted light intensity and its spectral

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Alvaro Otero, Carmen Goni, and Jim Syvertsen*

Six-year-old `Spring' navel [Citrus sinensis (L.). Osb.] orange trees were either totally defruited, 50% defruited or left fully cropped to study effects of fruit load on growth net gas exchange characteristics of mature leaves on seven selected clear days from Nov. 2001 through July 2002. Near harvest time, defruited trees had more shoot flushes, greater leaf dry wt per area (LDW/A) but lower net assimilation of CO2 (Ac) and stomatal conductance (gs) at midday than leaves on trees with fruit. Defruited trees had a higher ratio of internal to ambient CO2 (Ci/Ca) concentration in leaves implying internal limitations were dominant over stomatal limitation on Ac. Removal of half the crop increased individual fruit mass but reduced fruit color development. Half the trees were also shaded for four months prior to harvest with reflective 50% shade cloth to determine effects of lower leaf temperature (Tl) and leaf-to-air vapor pressure difference (D) on leaf responses. On selected clear days throughout the season, shade increased midday Ac and gs but decreased Ci/Ca compared to trees in the open implying that high mesophyll temperatures in sunlit leaves were more important than gs in limiting Ac. There were no effects of the shade treatment on canopy volume, yield or fruit size. Shaded fruit developed better external color but lower Brix than sun-exposed fruit. Thus, the presence of mature fruit maintained higher Ac than in leaves on defruited trees but high leaf temperatures and D reduced gs and Ac on warm days throughout the season.