No abstract

The finely‐ground woods and barks of 9 species of pine were allowed to decompose in soils in the presence and absence of additional nitrogen for periods of 63 to 800 days. Carbon dioxide evolution was measured at frequent intervals. The pine species studied were white, shortleaf, loblolly, slash, longleaf, ponderosa, western white, lodgepole, and sugar. An average of 16.2% of the wood carbon was oxidized in 60 days in the absence of extra nitrogen and 16.9% in its presence. The corresponding values for the barks were 8.7 and 8.6. The wood species showed variations in CO2 evolution during the 60‐day period, ranging from 8% for sugar pine to 51% for shortleaf pine. The variations for the barks were between 3.0% for white pine and 23.3% for lodgepole pine. Most of the pine woods decomposed somewhat more rapidly than did the other softwoods previously studied, but not nearly so rapidly as did the hardwoods. The pine barks are oxidized at about the same slow rate as are the other softwood barks.

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This study summarizes a large diverse dataset of methane (CH 4 ) fluxes measured from agricultural sites across the British Isles. A total of 53,976 manual static chamber measurements from 27 different sites were investigated to determine the magnitude of CH 4 fluxes from a variety of agricultural fields across the UK and Ireland. Our study shows that contrary to some studies, agricultural soils (both arable and grassland) are small net emitters of CH 4 rather than sinks.Mean fluxes measured from arable and grassland sites (excluding fertiliser and tillage events) were 0.11 ± 0.06 and 0.19 ± 0.09 nmol m −2 s −1 , respectively, and were not found to be significantly different (Welch t-test, p = 0.17). Using the values reported in this study, we estimate that an annual emission of 0.16 and 0.09 Mt of CO 2 -eq is expected from arable and grassland agricultural soils in the UK and Ireland (comparable to 0.3 and 0.7% of the current annual CH 4 emission inventories, respectively). Where CH 4 uptake occurs in soils, it is negligible compared to expected emissions of the application of animal manures and tillage events, which were both found to significantly increase CH 4 emissions in the immediate few days to months after events. Our study highlights that there are significant differences in CH 4 uptake and emissions between sites, and that these differences are partially the result of the moisture content of the soil (i.e., the aerobic status of the soil). We expect uptake of CH 4 to be more prevalent in drier soils where volumetric water content does not exceed 35% and emissions to be exponentially greater where agricultural fields become waterlogged.