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A. D. Matthias and W. E. Coates

Abstract

Wine grape (Vitis vinifera L.) vineyards in much of the desert Southwest are frequently exposed to intense solar radiation, high vapor pressure deficits, and high air temperatures. Although wine grape production in this region has increased during recent years, the harsh environment often results in growth conditions that may be suboptimal for photosynthesis and other plant processes, ultimately affecting fruit yield, wine color, and acidity.

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Pedro Perdomo, James A. Murphy, and Gerald A. Berkowitz

Understanding the factors influencing the performance of Kentucky bluegrass (Poa pratensis L.) cultivars under summer stress is necessary for developing criteria for identifying resistant germplasm. The objectives of this study were to evaluate two Kentucky bluegrass cultivars for leaf water (ψl) and osmotic potential (ψπ), stomatal resistance (Rs), leaf: air temperature differential (ΔT) and determine the relationship of these parameters to drought and heat tolerance. Stress-resistant (`Midnight') and susceptible (`Nugget') cultivars were evaluated in a field study during 1993 and 1994 under moisture-limiting conditions. Leaf water potential for `Nugget' was higher than for `Midnight' in 1993 and similar in 1994. `Midnight' had lower ψπ than `Nugget' during the evaluation period in 1994. `Midnight' maintained more open stomata (lower Rs) and lower ΔT than `Nugget' at the end of the dry down period when `Nugget' was showing visual signs of stress. `Midnight' and `Nugget' had similar root weight at the 0- to 45-cm depth zone in 1994. Lower basal osmotic potential (i.e., higher solute concentration) may be the physiological mechanism allowing larger stomatal aperture in `Midnight'. Greater transpirational cooling in `Midnight' relative to `Nugget' was correlated with higher turf quality for `Midnight'.

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Thomas R. Clarke

Irrigation scheduling can be improved by directly monitoring plant water status rather than depending solely on soil water content measurements or modeled evapotranspiration estimates. Plants receiving sufficient water through their roots have cooler leaves than those that are water stressed, leading to the development of the crop water stress index, which uses hand-held infrared thermometers as tools for scheduling irrigations. However, substantial error can occur in partial canopies when a downward-pointing infrared thermometer measures leaf temperature and the temperature of exposed, hot soil. To overcome this weakness, red and near-infrared images were combined mathematically as a vegetation index, which was used to provide a crop-specific measure of vegetative cover. Coupling the vegetation index with the paired radiant surface temperature from a thermal image, a trapezoidal two-dimensional index was empirically derived capable of detecting water stress even with a low percentage of canopy cover. Images acquired with airborne sensors over subsurface drip-irrigated muskmelon (Cucumis melo L.) fields demonstrated the method's ability to detect areas with clogged emitters, insufficient irrigation rate, and system water leaks. Although the procedure needs to be automated for faster image processing, the approach is an advance in irrigation scheduling and water stress detection technology.

Free access

Alexander X. Niemiera and Monika Goy

A study was conducted to determinethe feasibility of using crop water stress index (CWSI) to schedule irrigation of eight species of freeway landscape plants, Acacia redolens B.R. Maslin, Acacia salicina Lindl., Caesalpinia pulcherrima Sw., Cassia nemophila A. Cunn. ex Vogel, Cercidium floridum Benth., Eucalyptus microtheca F.J. Muell., Nerium oleander L., and Prosopis chilensis Mol. Nerium oleander and C. pulcherrima were suited to the use of the CWSI, tolerated repeated exposures to CWSI values of 0.6, and remained aesthetically acceptable. Irrigation of N. oleander via the CWSI resulted in a 19% reduction in water use, compared to the conventional method. CWSI data of other species were too variable, and, thus, irrigation could not be scheduled by CWSI values. Variability was attributed, in part, to lack of a dense canopy, which is necessary to fill the view of the infrared thermometer.

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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.

Open access

Joe J. Hanan

Abstract

Petal surface temperatures and temperature differentials between the petal surfaces and air, and between the petal surfaces and bottom of the calyx of fully open, red and white Dianthus caryophyllus flowers were examined under a variety of environmental conditions and transparent covers with the aid of an infrared thermometer. A number of multiple linear regression analyses were run on the data. Under certain conditions of wind velocity, solar radiation and air temperature, differentials of red carnation flowers exceeded 10° C, whereas white flowers were close to ambient air temperature. Lower radiant energy transmission by a cover reduced the effect of radiation level upon flower temperature, but increased petal surface temperatures and the differential between the petal surfaces and bottom of the flower. The differences were sufficient to partially explain results obtained in actual practice, to identify undesirable environmental parameters, and to emphasize a hitherto neglected area of research.

Free access

L. Lombardini and J.A. Flore

The recent development of small portable infrared thermometers has made canopy temperature an easily measured characteristc in the field. Our objective was to correlate a reduction of soil water with foliage temperature and to compare it with other indicators of plant stress (Pn, E, gs, leaf expansion, sap flow). During Summer 1998, we evaluated the responses of potted apple rootstocks (cultivars Budagowski 9, M9, and Mark) to soil water deficit. Irrigation was withheld for 7 days, and the canopy temperature (Tc) was measured daily with an infrared camera. Tc was always higher than air temperature (Ta). Tc between control and stress plants began to differentiate from day 3. In Mark, this difference was maintained until the end of the experiment. However, gas exchange in Mark seemed to be less affected by the stress than in the other two cultivars. At day 7, midday stomatal conductance (gs) was 38.0, 32.3, and 72.0 mmol·m–2·s–1 in Budagowski 9, M9, and Mark, respectively (control values varied between 161.6 and 164.3 mmol·m–2·s–1 for all the cultivars). Heat-pulse sapflow sensors installed on Mark indicated that the speed of the xylem sap was affected by the stress from day 4 (19-26 cm/h for the controls vs. 15–21 cm/h for the stressed plants). Specific details on the physiological data will be presented.

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Rohini Deshpande, D. P. Coyne, K. G. Hubbard, J. R. Steadman, E. P. Kerr, and Anne M. Parkhurst

The microclimate of Great Northern (GN) dry bean lines with diverse plant architecture was investigated in terms of white mold (WM) incidence and yield. A split-plot design was used with protected (3 weekly sprays of benomyl 0.9 KG HA-1 after flowering) and unprotected treatments as main-plots and GN lines as sub-plots in a WM nursery (1990, 1991). Canopy density, erectness, leaf area index, and plant characteristics were measured. `Starlight' (upright) and `Tara' (prostrate) were selected for detailed microclimate studies. An infrared thermometer, humidity sensor, and a thermistor were placed within the canopy at the advent of flowering. Leaf wetness and its duration were estimated by the leaf temperature in combination with air temperature and dewpoint temperature. `Starlight' showed later and shorter duration of leaf wetness, lower humidity, and WM and higher yield than `Tara'. Severe WM and reduced yields occurred also on all other susceptible entries with dense prostrate plant habits in the unprotected plots. Fractal analysis was done on the images of the canopy to quantify the light interception within the canopy.

Open access

A. Richard Bonanno and Harry J. Mack

Abstract

Two field experiments were conducted during 1981-1982 to determine the feasibility of using midday canopy temperatures, measured with an infrared radiation thermometer, for irrigation scheduling in ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) Treatments which allowed various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] to accumulate between irrigations were evaluated along with a treatment irrigated at 4 growth stages, a dry treatment, and a control treatment which was irrigated at -0.06 MPa soil water potential (SWP). Diurnal measurement of canopy and air temperatures indicated that the greatest differences between canopy and air temperature occurred near solar noon. In 1981, all treatments irrigated by an accumulation of positive SDD had reduced yields compared to the control SWP treatment. In 1982, under higher rainfall and lower air saturation vapor pressure deficits (VPD) than in 1981, yields of the SDD irrigated treatments were comparable to those obtained with the SWP treatment. Accumulation of positive SDD values to schedule irrigations was adequate when midday VPD values were low. However, when high VPD occurred, SDD values were always negative. A model is presented in which SDD values can be adjusted for environmental variability to more accurately schedule irrigations. Measurements of air temperatures within the canopy were made and compared to surface canopy temperatures measured with an infrared thermometer. Regression analysis showed that canopy temperature could be predicted using the air temperature within the canopy (R2 = 0.89). The sum of SDD values for the season was used to estimate canning maturity pod yield (R2 = 0.65).