Temperature Free-air Controlled Enhancement Research Articles

Seasonal assessment of greenhouse gas emissions from irrigated lowland rice fields under infrared warming

Rice fields are considered as one of the major sources of methane (CH4), and they also emit nitrous oxide (N2O). A field experiment was conducted at the International Rice Research Institute, Philippines, in 2010–2011 using a temperature free-air controlled enhancement (T-FACE) system. Our objectives were to assess (i) the suitability of the T-FACE system for flooded rice fields and (ii) seasonal variations in greenhouse gas emissions with and without experimental warming.This observation period included one wet season (WS), one dry season (DS), and a fallow season. The experimental warming, i.e., T-FACE system, was maintained by using six infrared heaters deployed in a hexagonal pattern over each plot (7.1m2). Set-point canopy temperatures of the warming treatment were 1.5 and 3.0°C higher than the reference plots during daytime and nighttime, respectively. Two warming treatments (i.e., heated and reference) were arranged in a randomized complete block design with three replications. Infrared warming increased rice canopy temperature by 1.1 and 2.6°C (0.4°C below the targeted set-point) during daytime and nighttime, respectively. On the other hand, only a marginal (0.4–0.5°C) increase was observed for both water and soil temperatures, likely because flood irrigation water flowed across the field. The warming (elevated canopy temperature) had no significant effects on CH4 or N2O emissions during the dry, wet, and fallow seasons. However, diel and seasonal variations in CH4 emissions were observed during the rice-growing and fallow periods. CH4 emissions were higher during the early afternoons, which was positively correlated with both soil and air temperatures. Similarly, CH4 emission rates increased with rice growth stage up to the reproductive stage. Moreover, cumulative CH4 emissions were 1.5 times higher in the 2011 DS than in the 2010 WS (50 and 34gCH4m−2, respectively). The 2-month fallow season (late May–early July 2011) under continuous flooding emitted 51gCH4m−2, which is similar to that in the 2011 DS. On the other hand, N2O emissions were not detected throughout the growing season, but an emission peak was observed after final drainage at maturity during the 2011 DS. Both rice-growing and fallow seasons were the major sources of CH4 emissions as long as the field was continuously flooded, while N2O was not detectable in continuously flooded soil. Infrared warming did not affect rice yields or yield components, probably because the general growing temperatures were near optimum, and the warming treatment was not sufficiently large to cause a significant effect.

Infrared Warming Affects Intrarow Soil Carbon Dioxide Efflux during Vegetative Growth of Spring Wheat

Global warming will likely affect carbon cycles in agricultural soils. Our objective was to deploy infrared (IR) warming to characterize the effect of global warming on soil temperature (Ts), volumetric soil‐water content (θs), and intrarow soil CO2 efflux (Φs) of an open‐field spring wheat (Triticum aestivum L. cv. Yecora Rojo) crop grown in the semiarid desert Southwest. A temperature free‐air controlled enhancement (T‐FACE) apparatus using IR heaters maintained canopy air temperature above 3.0‐m plots by 1.3 and 2.7°C (0.2 and 0.3°C below the targeted set‐points) during the diurnal and nocturnal periods, respectively. A randomized complete block (RCB) design with two IR warming treatments (i.e., Heated; Reference) in three replicates was planted on 10 Mar. and 1 Dec. 2008. Intrarow Ts, θs, and Φs were measured from emergence (bare soil) up until inflorescence emergence (canopy closure). Under ample soil water supply with high θs, midday Φs was 10% greater in Heated [4.1 μmol (CO2) m−2 s−1] compared with Reference [3.7 μmol (CO2) m−2 s−1]. In contrast, as the soil dried and θs decreased to a greater degree in Heated compared with Reference, a 10% decrease in Φs occurred in Heated compared with Reference. Overall, θs had the greatest impact on Φs, whereas it was responsive to Ts only under high θs. Accurate predictions of global climate change effects on Φs in agricultural soils require that interactive effects of Ts and θs be coupled. Infrared warming with T‐FACE proved to be an effective experimental methodology to investigate these interactive effects.

Cardinal temperatures for wheat leaf appearance as assessed from varied sowing dates and infrared warming

Accurate data on crop responses to temperature are essential for predicting the potential impacts of climate extremes. Air temperature can be precisely regulated in controlled environment chambers, but chambers seldom provide realistic radiation, photoperiod, wind and humidity regimes, which raise concerns as to whether responses quantified in such environments accurately reflect field performance. Field experiments employing sowing date (SD) and artificial warming treatments can provide a wide range of temperature regimes under otherwise natural field conditions. We analyzed temperature effects on main stem leaf appearance for the spring wheat (Triticum aestivum L.) cultivar Yecora Rojo using 15 sowing dates at Maricopa, AZ, USA. Six dates included infrared-based temperature free-air controlled enhancement (T-FACE) warming treatments. Mean air temperatures over the 15 periods of measurement varied from 11.6 to 33.2°C. Our objective was to characterize the effect of temperature on leaf number, emphasizing air temperatures above 20°C, a value often cited optimal for wheat development. An underlying concern was how different shapes of temperature responses functions might affect estimates of cardinal temperatures. For comparisons among four segmented linear functions, a quadratic function and two forms of the beta function, the best fit to the data was for a two-segment function with a base temperature (Tbase) of 1.9°C and an optimum (Toptl) of 22.2°C. In attempting to estimate a second, upper temperature for maximum development (Toptu), the estimation process failed. This likely reflected the low frequency of data from mean air temperatures over 25°C and possible severe stress responses at extreme low and high temperatures. The results further demonstrated the value of growing crops under a wide range of temperature regimes, which can be attained under field conditions through use of planting date and T-FACE treatments.

Infrared‐Warmed and Unwarmed Wheat Vegetation Indices Coalesce Using Canopy‐Temperature–Based Growing Degree Days

To determine the likely effects of global warming on field‐grown wheat (Triticum aestivum L.), a “Hot Serial Cereal” experiment was conducted—so‐called “Cereal” because wheat was the crop, “Serial” because the wheat was planted about every 6 wk for 2 yr, and “Hot” because infrared heaters were deployed on six of the planting dates in a temperature free‐air controlled enhancement (T‐FACE) system, which warmed the canopies of the Heated plots. During the experiment, measurements of canopy reflectance were made two to five times per week from which values of normalized difference vegetation index (NDVI) were calculated. As expected, curves of NDVI from the Heated plots vs. time and vs. growing degree days (GDD) computed from air temperatures generally were ahead of those from Reference plots. However, when plotted against GDD computed from canopy temperatures the curves coalesced, which gives confidence that the infrared‐heater treatment simulates natural warming and will produce plant responses not unlike those expected with future global warming. Biomass and grain yields were correlated with the areas under the NDVI vs. GDD curves for the air‐temperature‐based GDDs, but high variability prevented such a correlation to be detected using canopy‐temperature‐based GDD. Large differences existed between the total amounts of air or canopy temperature‐based GDDs required for wheat to mature in our irrigated fields in an arid region. This implies that GDD based on air temperatures should be regarded only as a local guide to plant development rates, whereas those based on canopy temperatures would be more universal.

Responses of time of anthesis and maturity to sowing dates and infrared warming in spring wheat

Reliable prediction of the potential impacts of global warming on agriculture requires accurate data on crop responses to elevated temperatures. Controlled environments can precisely regulate temperature but may impose unrealistic radiation, photoperiod and humidity regimes. Infrared warming with automatic control of temperature rise has shown potential for warming field plots above ambient temperatures, while avoiding such biases. In a field experiment conducted at Maricopa, AZ, we assessed the utility of a temperature free-air controlled enhancement (T-FACE) approach by comparing phenology of wheat from a series of six sowing date treatments using T-FACE and an additional nine sowing dates that exposed crops to an exceptionally wide range of air temperatures (<0 °C to >40 °C). The T-FACE treatments were intended to achieve a warming of +1.5 °C during the daytime and +3.0 °C at night; the achieved warming averaged +1.3 °C during daytime and +2.8 °C at night. T-FACE and sowing date treatments had large effects on phenology. A regression-based analysis of simulations with the CSM-CROPSIM-CERES model showed that effects of T-FACE on phenology were similar to what would be expected from equivalent changes in air temperature. However, systematic deviations from the expected 1-to-1 relation suggested that assumed cardinal temperatures for phenology should be revised. Based on the single cultivar and location, it appeared that the base temperature for emergence to anthesis should be reduced from 0 °C to −5 °C, whereas the base temperature for grain filling should be increased from 0 °C to 4 °C and the optimal temperature, from 30 °C to 34 °C. Both T-FACE and extreme sowing date treatments proved valuable for improving understanding of high temperature effects on plant processes, as required for accurate prediction of crop responses to elevated temperatures under climate change.

Gas exchange and water relations of spring wheat under full-season infrared warming

Gas exchange and water relations were evaluated under full-season in situ infrared (IR) warming for hard red spring wheat (Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the southwest USA. A temperature free-air controlled enhancement (T-FACE) apparatus utilizing IR heaters maintained canopy air temperature above 3.0 m Heated plots of wheat by 1.3 and 2.7 °C (0.2 and 0.3 °C below the targeted set-points of Reference plots with dummy heaters) during daytime and nighttime, respectively. Control plots had no apparatus. Every 6 weeks during 2007–2009 wheat was sown under the three warming treatments (i.e., Control, Heated, Reference) in three replicates in a 3 × 3 Latin square (LSQ) design on six plantings during 4 months (i.e., January, March, September, December), or in a natural temperature variation treatment (i.e., Control) in three replicates in a randomized complete block (RCB) design on nine plantings during 7 months (i.e., January, February, April, June, July, August, October). Soil temperature (Ts) and volumetric soil-water content (θs) were 1.3 °C warmer and 14% lower in Heated compared with Reference plots, respectively. Other than a 1% shading effect, no artifacts on gas exchange or water relations were associated with the IR warming apparatus. IR warming increased carbon gain characteristic of an increase in metabolic rates to higher temperature that may have been attributed to the well-watered wheat crop and the supplemental irrigation that minimized plant-to-air water vapor pressure differences between IR-warmed and nonwarmed plots. Nevertheless, seasonal oscillations in the IR warming response on carbon gain occurred. IR warming decreased leaf water status and provided thermal protection during freeze events. IR warming is an effective experimental methodology to investigate the impact of global climate change on agronomic cropping and natural ecosystems to a wide range of natural and artificially imposed air temperatures.

Comment on the comment by Amthor et al. on “Appropriate experimental ecosystem warming methods” by Aronson and McNulty

In a recent comment on the paper by Aronson and McNulty (2009) about “Appropriate experimental ecosystem warming methods by ecosystem, objective, and practicality”, Amthor et al. (2010) state that infrared lamps do not warm open-field plots by the mechanism expected with global warming. While this statement is correct, in the aftermath of their comment, confusion exists about how warming with infrared heaters can be related to global warming. This comment illustrates how infrared heating at “constant temperature rise” relates in a quantitative way to anticipated global warming. Amthor et al. (2010) also state that changes in vapor pressure gradient from leaf to atmosphere are an issue with infrared heating, but this problem can be minimized with supplemental irrigations in controlled amounts. Therefore, “constant temperature rise” infrared warming experiments with supplemental irrigations are a viable T-FACE (temperature free-air controlled enhancement) that can be used in combination with CO 2-FACE to produce conditions more representative of future open-fields than can be done with chambers with their many known artifacts.

Infrared heater arrays for warming ecosystem field plots

AbstractThere is a need for methodology to warm open‐field plots in order to study the likely effects of global warming on ecosystems in the future. Herein, we describe the development of arrays of more powerful and efficient infrared heaters with ceramic heating elements. By tilting the heaters at 45° from horizontal and combining six of them in a hexagonal array, good uniformity of warming was achieved across 3‐m‐diameter plots. Moreover, there do not appear to be obstacles (other than financial) to scaling to larger plots. The efficiency [ηh (%); thermal radiation out per electrical energy in] of these heaters was higher than that of the heaters used in most previous infrared heater experiments and can be described by: ηh= 10 + 25exp(− 0.17 u), where u is wind speed at 2 m height (m s− 1). Graphs are presented to estimate operating costs from degrees of warming, two types of plant canopy, and site windiness. Four such arrays were deployed over plots of grass at Haibei, Qinghai, China and another at Cheyenne, Wyoming, USA, along with corresponding reference plots with dummy heaters. Proportional integral derivative systems with infrared thermometers to sense canopy temperatures of the heated and reference plots were used to control the heater outputs. Over month‐long periods at both sites, about 75% of canopy temperature observations were within 0.5 °C of the set‐point temperature differences between heated and reference plots. Electrical power consumption per 3‐m‐diameter plot averaged 58 and 80 kW h day− 1 for Haibei and Cheyenne, respectively. However, the desired temperature differences were set lower at Haibei (1.2 °C daytime, 1.7 °C night) than Cheyenne (1.5 °C daytime, 3.0 °C night), and Cheyenne is a windier site. Thus, we conclude that these hexagonal arrays of ceramic infrared heaters can be a successful temperature free‐air‐controlled enhancement (T‐FACE) system for warming ecosystem field plots.

Theory and performance of an infrared heater for ecosystem warming

AbstractIn order to study the likely effects of global warming on future ecosystems, a method for applying a heating treatment to open‐field plant canopies (i.e. a temperature free‐air controlled enhancement (T‐FACE) system) is needed which will warm vegetation as expected by the future climate. One method which shows promise is infrared heating, but a theory of operation is needed for predicting the performance of infrared heaters. Therefore, a theoretical equation was derived to predict the thermal radiation power required to warm a plant canopy per degree rise in temperature per unit of heated land area. Another equation was derived to predict the thermal radiation efficiency of an incoloy rod infrared heater as a function of wind speed. An actual infrared heater system was also assembled which utilized two infrared thermometers to measure the temperature of a heated plot and that of an adjacent reference plot and which used proportional–integrative–derivative control of the heater to maintain a constant temperature difference between the two plots. Provided that it was not operated too high above the canopy, the heater system was able to maintain a constant set‐point difference very well. Furthermore, there was good agreement between the measured and theoretical unit thermal radiation power requirements when tested on a Sudan grass (Sorghum vulgare) canopy. One problem that has been identified for infrared heating of experimental plots is that the vapor pressure gradients (VPGs) from inside the leaves to the air outside would not be the same as would be expected if the warming were performed by heating the air everywhere (i.e. by global warming). Therefore, a theoretical equation was derived to compute how much water an infrared‐warmed plant would lose in normal air compared with what it would have lost in air which had been warmed at constant relative humidity, as is predicted with global warming. On an hourly or daily basis, it proposed that this amount of water could be added back to plants using a drip irrigation system as a first‐order correction to this VPG problem.