Abstract
To allow increased understanding of the global budget of atmospheric methane, individual methane sources require investigation. We have measured methane emissions from a California rice paddy during the entire 1982 growing season. A very strong seasonal dependence was observed. Methane emissions were highest in the last 2–3 weeks before harvest; daily emissions reached 5 g CH4/m2. Over the 100‐day season, daily emissions averaged about 0.25 g CH4/m2, higher than our previously reported values. Attempts to estimate global rice paddy emissions must recognize the possibility of seasonal variations. Soil temperature at 10‐cm depth correlated poorly with our measured fluxes; soil redox potential was a more reliable indicator.
Highlights
Deducingthe identitiesand sizesof the sourcesof atmo- 25 cm apart on May 11, 1982.The field sphericmethanehasbeena subjecot f interesto atmospheric was irrigatedas neededto maintain water depth at about chemistsandgeochemistfsor about20 years.Carbon14 data 11-15 cm throughthe growingseason,and the soil was a reviewedby EhhaltandSchmid[t1978]demonstrattehat over vertisol(Capayclay).Temperaturesand othersoiland water
Prior to planting,the field remethane, 33-49% was attributed to releasefrom the world's ceivedan applicationof ammoniumphosphate-ammonium rice paddies.In making theseestimates,Ehhalt and Schmidt sulfate(16-20-0)at the rate of 220 kg/ha
11,023 entire season should be valid. For both P1 and P2 fluxes were before Ciceroneand Shetter [1981], that the presenceof rice highestlate in the season.The total amountsemitted between plantsenhancesthe escapeof methanefrom soil.We interpret
Summary
Deducingthe identitiesand sizesof the sourcesof atmo- 25 cm apart on May 11, 1982.The field (areaabout0.5 ha) sphericmethanehasbeena subjecot f interesto atmospheric was irrigatedas neededto maintain water depth at about chemistsandgeochemistfsor about20 years.Carbon14 data 11-15 cm throughthe growingseason,and the soil was a reviewedby EhhaltandSchmid[t1978]demonstrattehat over vertisol(Capayclay).Temperaturesand othersoiland water. It has become important to quantify the grator)rather than by peak height.During eachsuchcolindividual methanesourcesand the temporalchangesin these lection for flux measurements,we measuredtemperatures sourcesi,ncludingthe most recentsuggestionosf potentially of ambientair, air insidethe collector,soil (at 10-cmdepth), significantsources,for example,termites [Zimmermanet al., and rice height.Soil redox potential,Eh, was measuredby 1982;RasmusseanndKhalil, 1983] and biomassburning [Crut- meansof a platinumelectrodereferredto a calomehl alfcell. In thispaperwe presentnewfieldmeasurementosf methane riceplants,butbecausecountingstalkswasdifficultphysically emissionsfrom ricepaddies.The data showstrongdependence andbecausewe soughtto avoidbendingandjostlingthe rice of the methaneemissionrate on time elapsedin the growing stalks,thisgoalwasnot attainedreliably.
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