Seasonal assessment of greenhouse gas emission from irrigated lowland rice field under infrared warming

Authors: GAIHREA, Y - International Rice Research Institute; WASSMAN, R - International Rice Research Institute; TIROL-PADREA, A - International Rice Research Institute; VILLEGAS-PANGGA, G - University Of The Philippines; AQUINO, E - International Rice Research Institute; Kimball, Bruce

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2013
Publication Date: 12/19/2013
Publication URL: http://handle.nal.usda.gov/10113/58157
Citation: Gaihrea, Y.K., Wassman, R., Tirol-Padrea, A., Villegas-Pangga, G., Aquino, E., Kimball, B.A. 2013. Seasonal assessment of greenhouse gas emission from irrigated lowland rice field under infrared warming. Agriculture, Ecosystems and Environment. 18:88-100.

Interpretive Summary: In order to study the likely effects of global warming on future rice production, upon which a large fraction of Earth’s population depends for food, 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 the rice vegetation as expected by the future climate. One approach which has shown promise is infrared heating, which has previously worked well with upland crops such as wheat. Therefore, a T-FACE experiment was implemented on paddy rice for wet, dry, and fallow seasons. The T-FACE system increased rice canopy temperatures by 1.1 and 2.6 °C (0.4 °C below the targeted set-point) during daytime and nighttime, respectively, but only marginal increases of (0.4-0.5 °C) were observed in soil and water temperatures, probably because the flood irrigation water flowed across the field. Consequently, no significant changes were observed in emissions of greenhouse gases from the soil. Similarly, because temperatures were near but below the optimum for rice growth, no significant changes were detected in rice yields. These results show that isolation of the heated plot irrigation system must be done to study greenhouse gas emissions and that so long as global warming does not tip rice yields over their optimum, which may not generally occur, rice yields will not be hurt by global warming. This research will benefit all consumers of rice and other food crops.

Technical Abstract: 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 (7.1 m2). Setpoint canopy temperatures of the warming treatment were 1.5 and 3.0 °C higher than 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 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, diurnal and seasonal variations in CH4 emission were observed during the rice-growing and fallow periods. CH4 emission was 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 emission was 1.5 times higher in 2011 DS than in 2010 WS (50 and 34 g CH4 m-2, respectively). The 2-month fallow season (May-July 2011) under continuous flooding emitted 51 g CH4 m-2, which is similar to that in 2011 DS. On the other hand, N2O emission was not detected throughout the growing season, but an emission peak was observed after final drainage at maturity during 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. No effects of the infrared warming treatment were found on the rice yields or yield components, probably because the general growing temperatures were near optimum, and the warming treatment was not sufficiently large to cause the rice to experience damaging temperatures