Abstracts

Ajayi, A.E. and Olufayo, A.A. 2004, 'Evaluation of Two Temperature Stress Indices to Estimate Grain Sorghum Yield and Evapotranspiration', Agronomy Journal, vol. 96, pp. 1282-1287.

This study was performed to examine the relationship between canopy temperature (T_c)-based stress indices and grain yield and evapotranspiration (ET) of sorghum [Sorghum bicolor (L.) Moench]. The crop was subjected to 14 differentially irrigated treatments of which two were controls maintained at well-watered and dry conditions during three consecutive years. Soil water content and T_c were measured, and relationships between T_c-based stress indices [stress degree day (SDD), temperature stress day (TSD), and crop water stressed index (CWSI)] and yield as well as ET were examined. The T_c-air temperature (T_a) difference varied from -2 to +8°C in the stressed treatments and maintained a negative value for most of the time in the well-watered treatment. The relationship between T_c - T_a and vapor pressure deficit, commonly referred to as baseline in the determination of CWSI, was examined on function of wind speed and global solar radiation. Although observations showed that T_c can be influenced by climatic condition, this study confirmed that it can serve as a useful indicator of water stress in the case of sorghum. High correlation found between T_c-based stress indices TSD, SDD, and CWSI and ET as well as grain yield suggest the possibility of using these relationships for predictive purposes.

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American Society for Testing and Materials 2001, 'Standard Test Methods for Radiation Thermometers (Single Waveband Type). Designation: E 1256 - 95 (Reapproved 2001)', in 2001 Annual Book of ASTM Standards, eds, American Society for Testing and Materials,, West Conshohocken.

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Bugbee, B., Droter, M., et al. 1998, 'Evaluation and Modification of Commercial Infra-red Transducers for Leaf Temperature Measurement', Advances in Space Research, vol. 22, no. 10, pp. 1425-1434.

Accurate measurement of the leaf to air temperature gradient is crucial for the determination of stomatal conductance and other plant responses in both single leaves and in plant canopies. This gradient is often less than 1°C, which means that leaf temperature must be known to within about ±0.1°C. This is a challenging task, but new, miniature infra-red transducers from Exergen Corporation (Newton, MA) and Everest Interscience (Tucson, AZ) can be modified and calibrated to achieve this accuracy. The sensors must be modified to add thermal mass and the Exergen sensor requires a measurement of sensor body temperature. Significant error is caused by the discharge of a capacitor in the standard Exergen sensor, but we tested it without the capacitor. The sensors respond rapidly to changes in target temperature, but require 2 to 10 minutes to respond to changes in sensor body temperature, which is often the largest source of error. A new, sensitive method for measuring field of view indicates substantial peripheral vision for both sensors and a wider field of view than specified by the manufacturers. Here we describe sensor output as a function of target and sensor body temperatures, and provide a generic (sensor independent) equation that can be used to achieve ±0.2 C accuracy with Exergen sensors. The equation was developed and verified using two black body calibrators.

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Bugbee, B., Monje, O., et al. 1996, 'Quantifying Energy and Mass Transfer in Crop Canopies: Sensors for Measurement of Temperature and Air Velocity', Advances in Space Research, vol. 18, no. 4-5, pp. 149-156.

Here we report on the in situ performance of inexpensive, miniature sensors that have increased our ability to measure mass and energy fluxes from plant canopies in controlled environments: 1. Surface temperature. Canopy temperature measurements indicate changes in stomatal aperture and thus latent and sensible heat fluxes. Infrared transducers from two manufactures (Exergen Corporation, Newton, MA; and Everest Interscience, Tucson, AZ, USA) have recently become available. Transducer accuracy matched that of a more expensive hand-held infrared thermometer. 2. Air velocity varies above and within plant canopies and is an important component in mass and energy transfer models. We tested commercially-available needle, heat-transfer anemometers (1 x 50 mm cylinder) that consist of a fine-wire thermocouple and a heater inside a hypodermic needle. The needle is heated and wind speed determined from the temperature rise above ambient. These sensors are particularly useful in measuring the low wind speeds found within plant canopies. 3. Accurate measurements of air temperature adjacent to plant leaves facilitates transport phenomena modeling. We quantified the effect of radiation and air velocity on temperature rise in thermocouples from 10 to 500 mm. At high radiation loads and low wind speeds, temperature errors were as large as 7°C above air temperature.

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Diaz, R.A., Matthias, A.D., et al. 1983, 'Evapotranspiration and Yield Estimation of Spring Wheat from Canopy Temperature', Agronomy Journal, vol. 75, pp. 805-810.

Canopy temperature indices have been shown to be related to evapotranspiration (ET) and grain yield (Y) for many crops at various locations. The purpose of this study was to evaluate three indices at a location different from where the indices were developed. The indices were the stress-degree-day (SDD), temperature-stress-day (TSD), and the crop-water-stress index (CWSI), and were tested at Logan, Utah on spring wheat (Triticum aestivum L. var. Fieldwin). Planting dates were 14 Apr., 28 Apr., and 19 May 1980. Canopy temperatures in differentially irrigated plots (36 x 3 m) were measured by infrared thermometry at midday from growth stages of heading to maturity. Net radiation, wind speed, humidity, and air temperature data were collected. Neutron meter measurements were used to calculate ET. Summations of SDD (ΣSDD) and TSD (ΣTSD) and mean values of CWSI were calculated. Linear regression analysis for each planting showed large goodness of fit (r² > 0.93) for ET vs. STSD, and for ET vs. SSDD (r² > 0.86). Large r² values were obtained with Y vs. ΣTSD and Y vs. ΣSDD data. For the combined data from all plantings, r² ranged from 0.90 for the ET vs. ΣSDD data to 0.21 for the Y vs. STSD data. Slopes and intercepts of individual regression lines were significantly (α = 0.05) different. Goodness of fit of relative ET deficit with mean CWSI for the combined plantings was r² = 0.86, and for relative Y decrease with mean CWSI, r² = 0.78. Results indicate that SDD may be most suitable for wheat yield assessment and water management in northern Utah.

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Fuchs, M. 1990, 'Canopy Thermal Infrared Observations', in Instrumentaiton for Studying Vegetation Canopies for Remote Sensing in Optical and Thermal Infrared Regions, eds. S.G. Narendra and J.M. Norman, Harwood Academic Publishers, London, 5, pp. 323-333

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Fuchs, M. and Tanner, C.B. 1966, 'Infrared Thermometry of Vegetation', Agronomy Journal, vol. 58, pp. 597-601.

Infrared thermometers with a bandpass filter from 8µ to 13µ can be used to measure the real temperature of vegetal surfaces with errors in the range of 0.1C to 0.3C. To do this the emissivity must be either known or determined and a correction accounting for the reflected radiation from the surroundings must be made. Values of emissivities found for dense canopies of alfalfa and of sudangrass were between 0.97 and 0.98. Emissivities of single leaves of snap bean and tobacco were 0.96 and 0.97, respectively. Depending upon the radiation of the surroundings corrections of +0.6C to .+1.4C had to be added to the apparent radiative temperature of these surfaces in order to yield real surface temperature.

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Garrot, D.J., Gibson Jr, R.D., et al. 1998, 'The Response of Table Grape Growth, Production, and Ripening to Water Stress', in 1998 Citrus and Deciduous Fruit and Nut Research Report, eds G. Wright and M. Kilby, University of Arizona, Tuscon.

Four year old 'Flame Seedless' grapevines located in a commercial vineyard subjected to increased water stress levels based on infrared canopy temperatures and the Crop Water Stress Index (CWSI) for two years. CWSI levels were approximately .18, .30 and .33 for the wet, medium and dry treatments. In the first year there were no significant differences in yield however, there was a significant reduction in the amount of water applied in both the medium and dry treatments when compared to the wet treatment. In addition, the wet treatment had significantly greater growth during the first growing season when comparing pruning weights.

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Garrot Jr, D.J., Ottman, M.J., et al. 1994, 'Quantifying Wheat Water Stress with the Crop Water Stress Index to Schedule Irrigations', Agronomy Journal, vol. 86, pp. 195-199.

The relationship between the timing and amount of applied irrigation water and grain yield has not been well defined for durum wheat (Triticum turgidum L. var. durum) grown under irrigation in arid regions. With rising water costs and decreasing water supplies, grain growers will have to optimize yield for given levels of water inputs if they are to remain profitable. Small-plot field studies were conducted in 1986 and 1987 at Marana, AZ, to (i) test the feasibility of using the crop water stress index (CWSI) to schedule wheat irrigations and (ii) determine relationships among CWSI, grain production, and water applied. Highest grain production was attained when irrigations were scheduled at CWSI values averaging 0.37 units in 1986 and 0.30 units in 1987. Scheduling irrigations with lower CWSI values did not increase grain production, but required more water. Delaying irrigation by scheduling irrigations at CWSI values exceeding the optimum values reduced grain production.

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Hattendorf, M.J., Carlson, R.E., et al. 1988, 'Crop Water Stress Index and Yield of Water-Deficit-Stressed Alfalfa', Agronomy Journal, vol. 80, pp. 871-875.

The yield relationship of water-deficit-stressed alfalfa (Medicago sativa L.) with the Crop Water Stress Index (CWSI) may be dynamic over the alfalfa harvest period. This investigation was conducted to define the alfalfa yield-CWSI relationship(s), to test possible advantages of using the CWSI over the canopy-minus-air temperature (Tc-Ta) differential, and to combine the yield-CWSI relationship with a growth function. 'Apollo II' alfalfa was grown for 2 yr in 100-L containers set into the ground and protected from rain by a movable shelter. The soil was a Nicollet silt loam topsoil (fine-loamy, mixed, mesic Aquic Hapludoll). Treatments were irrigation levels of 112, 100, 88, 77, and 65% field capacity. Five harvests were taken at 7-d intervals beginning 21 d after an initial clipping. Canopy temperatures were taken daily with an infrared thermometer. A series of exponential yield-CWSI curves resulted from the sequential harvests. Yield reductions of about 10 and 20% resulted from mean CWSI of 0.05 and 0.10, respectively, over 42-d periods. The Gompertz growth function was modified for water-deficit-stress by combining it with the exponential yield-CWSI relationship. Vapor-pressure deficit (VPD) effectively normalized the Tc-Ta data, allowing yield data of the 2 yr to be combined in the yield-mean CWSI relationship. Yield and Tc-Ta data not normalized for VPD showed clear separation by year for slight VPD differences. Alfalfa yield response to water-deficit-stress over time appeared to be adequately described by the combined Gompertz function and the yield-CWSI (Tc-Ta normalized for VPD) curves.

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Irmak, S., Haman, D.Z., et al. 2000, 'Determination of Crop Water Stress Index for Irrigation Timing and Yield Estimation of Corn', Agronomy Journal, vol. 92, pp. 1221-1227.

Corn (Zea mays L.) grown under a Mediterranean semiarid climate requires supplemental irrigation to maximize the grain yield. Since the cost of irrigation application has been increasing, elimination of unnecessary irrigation applications would improve economics of corn production. There has been much interest in the crop water stress index (CWSI) as a potential tool for irrigation scheduling and yield estimation. An experiment was conducted to monitor and quantify water stress, and to develop parameters for irrigation scheduling and grain yield of summer-grown corn as a function of CWSI under Mediterranean semiarid cropping conditions. Three irrigation treatments were based on replenishing the 0.9-m deep root zone to field capacity when the soil water level dropped to 25, 50, and 75% of available water holding capacity (AWHC). A dryland treatment was also included. The lower (nonstressed) and upper (stressed) baselines were measured to calculate CWSI. An equation that can be used to calculate the yield potential of summer-grown corn under a Mediterranean climate was developed using the relationship between the corn grain yield and the seasonal mean CWSI. Permitting the seasonal average CWSI value to exceed more than 0.22 resulted in decreased corn grain yield. The CWSI behaved as expected, dropping to near zero following an irrigation and increasing gradually as corn plants depleted soil water reserves. We concluded that CWSI is a useful tool to monitor and quantify the water stress of corn under a Mediterranean climate.

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Jackson, R.D. 1982, 'Canopy Temperature and Crop Water Stress', in Advances in Irrigation, eds. G.S. Campbell and M.D. Campbell, Academic Press, New York, 1, pp. 43-85

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Jackson, R.D., Idso, S.B., et al. 1981, 'Canopy Temperature as a Crop Water Stress Indicator', Water Resources Research, vol. 17, no. 4, pp. 1133-1138.

Canopy temperatures, obtained by infrared thermometry, along with wet- and dry-bulb air temperatures and an estimate of net radiation were used in equations derived from energy balance considerations to calculate a crop water stress index (CWSI). Theoretical limits were developed for the canopy air temperature difference as related to the air vapor pressure deficit. The CWSI was shown to be equal to 1 - E/E_p, the ratio of actual to potential evapotranspiration obtained from the Penman-Monteith equation. Four experimental plots, planted to wheat, received postemergence irrigations at different times to create different degrees of water stress. Pertinent variables were measured between 1340 and 1400 each day (except some weekends). The CWSI, plotted as a function of time, closely paralleled a plot of the extractable soil water in the 0- to 1.1-m zone. The usefulness and limitations of the index are discussed.

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Kirkham, M.B. 2005, 'Chapter 24: Measurement of Canopy Temperature with Infrared Thermometers', in Principles of Soil and Plant Water Relations, ed^eds, Elsevier, Burlington, pp. 425-435

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Sadler, E.J., Bauer, P.J., et al. 2000, 'Site-Specific Analysis of a Droughted Corn Crop: II. Water Use and Stress', Agronomy Journal, vol. 92, pp. 403-410.

In the southeastern USA Coastal Plain, spatial variation in soils causes extreme spatial variation in grain yield, as seen in yield maps. Corn (Zea mays L.) appears to be particularly susceptible to soil variation, especially during periods of drought. Our objectives were to compare variation in water use and stress of corn within and among soil map units. In one field, at two sites in each of four map units, we measured site-specific effects of soil variation on crop water use from 40 d after planting until after maturity using a time-domain reflectometer (TDR). On 4 d during vegetative growth, drought stress was evaluated on eight transects using infrared thermometer (IRT) measurements of canopy temperature (T_c). During the most severe drought, visibly stressed areas had canopy-air temperature differences (T_c - T_a) > 10°C, yet other areas remained <2°C. Two days after a 46-mm rain, T_c - T_a was near zero over the whole field, indicating little water stress. The time series of TDR measurements produced estimates of daily evapotranspiration, runoff, and infiltration; site-to-site differences in these dominated the water balance. Water stress, inferred from water use, matched that inferred earlier from yield components. In sum, corn at the eight sites arrived at final water use via fundamentally different paths. Further, variation between sites within soils was significant, indicating that soil map units are not homogenous with respect to water relations. These results underscore the need for within-season observations of crop water use and stress to augment interpretation of site-specific yield maps.

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Schaamfsma, A.W., Whitfield, G.H., et al. 1993, 'Evaluation of Infrared Thermometry as a Non-destructive Method to Detect Feeding on Corn Roots by the Western Corn Rootworm (Coleoptera: Chrysomelidae)', The Canadian Entomologist, vol. 125, pp. 643-655.

Infrared thermometry was investigated as a diagnostic tool to detect root injury in corn caused by feeding of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Plots were infested with 50-1000 eggs per plant, nd the study was conducted over 2 years. Differences (P<0.05) in canopy temperatures were detected in severly infested plots in 6 out of 13 and 7 out of 11 days on which measurements were made during the period of feeding by rootworm larvae in 1989 and 1990, respectively. Temperature differences between the air and leaves from infested plants were never greater than 3.5°C and usually occurred within ±1°C. Feeding by rootworm larvae at infestation levels of less than 200 eggs per plant could not be detected with infrared thermometry. Above densities of 200 eggs pr plant, increases in canopy temperatures corresponded with increases in the level of infestation with rootworm eggs, and with reduced plant height, and lower grain yield. Losses in grain yield due to rootworm infestation were manifested through smaller cobs and fewer seeds per cob. Kernel weight was not affected by rootworm feeding. Crop maturity was delayed at infestation levels of 1000 eggs per plant. Elevated canopy temperatures induced by rootworm feeding were detected through infrared thermometry in commercial corn fields, however differences (P<0.05) in canopy temperatures were noted only after 10 July. Although these data show that elevated canopy temperatures induced by rootworm feeding can be detected with infrared thermometry, some inconsistency in results were observed. Various reasons for why the technique was not more reliable are discussed.

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