Automated Chamber Measurements of Methane and Nitrous Oxide Flux in a Flooded Rice Soil: II. Fallow Period Emissions

Abstract

Methane and N2O are radiatively important gases that are emitted from waterlogged soils. Automated chamber measurements of CH4 and N2O fluxes were carried out at the International Rice Research Institute in the Philippines in flooded rice (Oryza sativa L.) and fallow rice fields 24 h a day between December 1992 and April 1994. This period included three 5‐ to 11‐wk rainfed fallow periods. During the first two fallows, the soil was generally aerobic, and moderate amounts of NO3 accumulated (7–20 kg NO3‐N ha‐1). Moderately high, continuous N2O fluxes were evident during these two fallow periods. This N2O was apparently emitted during nitrification of mineralized organic N in the topsoil and possibly from denitrification in the wet subsoil. Nitrous oxide fluxes were highest (up to 80 mg N2O‐N m‐2 d‐1) immediately after rainfalls >20 mm, and following the establishment of flooding for rice at the end of the fallows. Acetylene inhibition in intact cores at these times showed that more N2 was produced than N2O. Denitrification of accumulated NO3 was therefore occurring after the wetting events. Methane emissions were generally absent during the fallow periods. Two exceptions were immediately after rice harvest and 1 to 2 wk after the establishment of the permanent flood. Following flooding and green manure (GM; Sesbania rostrata L.) incorporation, CH4 fluxes appeared within 7 d. During the third fallow period, which was unusually wet, no NO3 accumulated in the soil. Nitrous oxide emissions were not significant, and low levels of CH4 fluxes persisted throughout this fallow period. This study demonstrates that rice soils in the fallow periods can be significant sources of N2O, and during wet fallow seasons, important sources of CH4 as well.

Effects of alternate wetting and drying technique on greenhouse gas emissions from irrigated rice paddy in Central Luzon, Philippines

“…The early drainage or soil drying after only a few days of N application resulted in high N 2 O emissions due to dry conditions in DS, although, the Philippines' recommendation during fertilizer application is to maintain 3-5 cm ponded water. As observed in many previous field studies (e.g., Bronson et al 1997;Sander et al 2014;Sun et al 2016;Tariq et al 2017), substantial N 2 O fluxes were often observed after N fertilizer topdressing during temporal drained periods under AWD and AWDS, especially for DS. In other words, as reported by Zou et al (2005), keeping flooded soil conditions could minimize the N 2 O flux peaks observed after the topdressing.…”

“…Because rice root system would not be well established by then, ebullition was a plausible pathway of the CH 4 emission (Schutz et al 1989). Bronson et al (1997) reported that CH 4 production was enhanced after an extended saturated soil condition. Corton et al (2000) observed the initial high peaks of CH 4 flux at the vegetative stage due to the anaerobic decomposition of rice straw incorporated.…”

N2O and NO emission from agricultural fields and soils under natural vegetation: summarizing available measurement data and modeling of global annual emissions

“…Inundation in wetland rice promote anaerobic conditions, whereby N 2 O is more likely to be re-consumed before being emitted from the soil (Davidson 1991). High N 2 O emissions after drainage of the paddy field (Bronson et al 1997) are not included in most measurements in our data set. Low N 2 O emissions from grassland may be related to the long growing season of grass and higher N uptake than in crops with shorter growing periods.…”

Nitrogen Transformations in Submerged Soils

“…The NO 3 − is denitrifi ed when the soil becomes saturated by rain or irrigation . Rain in the fallow period between rice crops stimulates the emission of N 2 O (Bronson et al, 1997c;Abao et al, 2000), which is associated with nitrifi cation-denitrifi cation. Appreciable NO 3 − can accumulate during the fallow period particularly when periodic rains help maintain a favorable soil water content for nitrifi cation .…”