Measuring yield-reducing plant water potential depressions in wheat by infrared thermometry

Summary Measurements of foliage and air wet- and dry-bulb temperatures were made over six differentially irrigated plots of Produra wheat grown at Phoenix, Arizona, in the spring of 1976. These data were used to evaluate a newly developed plant water stress index each day from the initiation of heading to the commencement of senescence. Daily measurements on total plant water potential were also obtained over this period; and after demonstrating how the atmospheric-induced component can be removed from these data, the resultant soil-induced component was plotted as a function of the new water stress index. The result was a simple linear relationship, which was found to be identical to one previously derived for alfalfa. Finally, it was shown that grain yield was directly related to the mean plant water stress index over the reproductive growth period from heading to senescence.Contribution from Agricultural Research, Science and Education Administration, US Department of AgricultureResearch physicist, soil scientist, research physicist, and research entomologist, respectively     

Quantifying effects of atmospheric CO2 enrichment on stomatal conductance and evapotranspiration of water hyacinth via infrared thermometry

Measurements of stomatal conductance and evaporative water loss from two tanks of water hyacinths growing at Phoenix, AZ, one under ambient conditions and one considerably enriched in atmospheric CO₂, are reported. Stomatal conductances of plants in the CO₂-enriched treatment were reduced to values half as great as those of plants in the ambient treatment at a mean mid-day CO₂ concentration of 550 ppm, which resulted in a 22% decrease in total evaporative water loss; while in going from an ambient CO₂ concentration of 310 ppm to a doubled concentration of 620 ppm there was a 27% decrease in evaporative water loss. Both of these physiological responses were well characterized by the Idso—Jackson plant water stress index. Additionally, it was found that the stomatal response to increasing atmospheric CO₂ was identical to that induced by removing water from the plant roots, and that the reduction in evaporative water loss with increasing atmospheric CO₂ was an inverse linear function of the plant water stress index — both of which phenomena had previously been theorized but never before experimentally verified.     

The Climatological Significance of a Doubling of Earth's Atmospheric Carbon Dioxide Concentration

The mean global increase in thermal radiation received at the surface of the earth as a consequence of a doubling of the atmospheric carbon dioxide content is calculated to be 2.28 watts per square meter. Multiplying this forcing function by the atmosphere's surface air temperature response function, which has recently been determined by three independent experimental analyses to have a mean global value of 0.113 K per watt per square meter, yields a value of 相似文献   

Remote sensing for agricultural water management and crop yield prediction

Research we have conducted over the past several years relative to agricultural application of remote sensing is reviewed. In addition, new data are presented from recent experiments reported here for the first time.The subjects treated are soil moisture, evaporation, irrigation scheduling, and crop yield estimation. The analyses indicate that we have the technology at hand to successfully integrate remote sensing techniques into agricultural operations designed to enhance production via intelligent water management.Avenues for additional fruitful research are indicated.     

Remote-sensing of crop yields

Our research efforts with durum wheat have led to the development of the SDD concept. Its application makes possible crop yield estimates from remotely acquired canopy temperatures and auxiliary air temperature measurements obtained during the period from head emergence to the cessation of head growth. Canopy albedo measurements appear adequate to delineate this critical period, making the technique potentially adaptable to predictions of crop yields by remote-sensing. The trifactor nomograms produced from combinations of the linear regression equations also suggest that the SDD concept may be used for scheduling irrigations by remote-sensing.     

Effects of panicles on infrared thermometer measurements of canopy temperature in wheat

A study was conducted in Phoenix, AZ on stressed and unstressed field plots of Anza wheat (Triticum aestivum L.) on an Avondale loam soil (a fine, loamy, mixed calcareous hyperthermic Anthropic Torrifluvent) to determine effects of panicles on the apparent canopy temperature and their consequent impact on the estimation of crop stress. The panicles were removed from a 1.5 × 4-m sample of each plot by extracting the peduncle from the upper sheath. For each treatment canopy radiative temperature measurements were made from vertical and oblique angles (30° from the horizontal), using an 8° field-of-view (FOV) infrared thermometer, at half-hour intervals from sunrise to sunset on 20, 22, and 30 April. Complementary measurements included leaf water potential and leaf diffusive resistance.Apparent canopy temperatures obtained from the oblique view of the canopy with panicles and under well-watered conditions were 2°C warmer than those of the unstressed canopy without panicles. In the stressed plot the canopy with panicles was 1°C cooler than that without panicles, but this effect was only noticed around 1200 MST. The temperature difference between viewing angles was apparently caused by different percentages of panicle area viewed by the radiometer. In the vertical view panicles contributed to 3% of the total viewed area while at the 30° oblique view panicles comprised 40% of the area. Since energy balance calculations of a non-transpiring cylinder with dimensions similar to a typical wheat panicle showed its temperature would remain very close to that of the surrounding air, canopy temperatures were adjusted for the proportion of panicles viewed assuming they were in equilibrium with air temperature. Results showed the corrected canopy temperatures of the canopy with panicles were the same as those measured in the canopy without panicles. Such a correction is necessary to avoid an overestimate of the stress level and an underestimate of differences between treatments. Crops with non-transpiring and/or well-ventilated morphological structures above the foliage will require this correction if radiative canopy temperatures are to be used in irrigation management programs or stress detection studies.