Fluxes of methane and carbon dioxide from soil under forest, grazing land, irrigated rice and rainfed field crops in a watershed of Nepal |
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Authors: | Keshab D Awasthi Bishal K Sitaula Bal Ram Singh Roshan M Bajracharya |
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Institution: | (1) Department of Plant and Environmental Sciences, Agricultural University of Norway, P.O. Box 5003, 1432 Ås, Norway;(2) Department of Soil Conservation and Watershed Management, Institute of Forestry, P.O. Box 43, Pokhara, Nepal;(3) Noragric, Agricultural University of Norway, P.O. Box 5003, Ås, Norway;(4) Kathmandu University, Dhulikhel, Nepal |
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Abstract: | Field evolution of CH4 and CO2 from soils under four dominant land uses in the Mardi watershed, western Nepal, were monitored at 15-day intervals for 1 year using closed chamber techniques. The CH4 oxidation rate (mean±SE, g CH4 m–2 h–1) in the forest (22.8±6) was significantly higher than under grazing land (14±2) and an upland rainfed maize and millet system (Bari) (2.6±0.9). Irrigated rice fields (Khet) showed an oxidation rate of 6±0.8 g CH4 m–2 h–1 in the dry season (December–May) but emitted a mean rate of 131 g CH4 m–2 h–1 in the rainy season and autumn (June–October). The evolution of CO2 ranged from 10 mg CO2 m–2 h–1 in the Bari in January to 1,610 mg CO2 m–2 h–1 in the forest in July. Higher evolution of CO2 (mean±SE, mg CO2 m–2 h–1) was observed in the Bari (399±39) and forest (357±36) compared to Khet (246±25) and grazing (206±20) lands. The annual emission of CO2 evolution varied from 86.6 to 1,836 g CO2 m–2 year–1. The activation energy for CH4 and CO2 varied between 16–283 and 80–117 kJ mol–1, respectively. The estimated temperature coefficient for CO2 emission varied from 2.5 to 5.0. Temperature explained 46–51% of the variation in CO2 evolution, whereas it explained only 4–36% of the variation in CH4 evolution. |
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Keywords: | Carbon dioxide Greenhouse gases Land use Methane Nepal |
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