Nitrous oxide, nitric oxide, and methane fluxes from soils following clearing and burning of tropical secondary forest

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Abstract
Conversion of humid tropical forest to agriculture significantly alters trace gas emissions from soils. We report nitrous oxide (N2O), nitric oxide (NO), and methane (CH4) fluxes from secondary forest soils prior to and during deforestation, and throughout the first agricultural cropping. Annual average nitrogen oxide emissions from forest soils were 1.5 ng N cm−2h−1for N2O and 0.9 ng N cm−2h−1for NO. Forest clearing increased the level of extractable nitrate in soils and average nitrogen oxides fluxes (2.7 ng N cm−2h−1for N2O, and 8.1 ng N cm−2h−1for NO). Immediately after biomass burning, short‐term peaks of N2O and NO (123 ng N cm−2h−1for N2O, and 41 ng N cm−2h−1for NO) were superimposed on generally increased fluxes. Peak emissions declined within 3 days after burning. Postburn fluxes stayed higher than measured on adjacent forest sites for 3–4 months (averages for postburn fluxes were 17.5 ng N cm−2h−1for N2O, and 19.2 ng N cm−2h−1for NO). Increased N2O and NO emissions after clearing and until cropping were probably due to a combination of increased rates of nitrogen cycling and higher gaseous diffusion in drying soils. Compared to emissions from young pastures in the region, fluxes of nitrogen oxides from unfertilized agricultural areas were low (3.9 ng N cm−2h−1for N2O and 3.4 ng N cm−2h−1for NO), probably due to nitrogen uptake by fast growing corn plants and losses by leaching with draining soil water in the wet season. Variation in CH4fluxes was high for all land use periods. Forest soils consumed an average of 1.0 mg CH4m−2d−1, which slightly increased in drier soils after clearing (1.2 mg CH4m−2d−1). Postburn CH4consumption by soils was slightly reduced (0.8 mg CH4m−2d−1) compared to forest soils. Unfertilized agricultural soils consumed less CH4than forest soils.