Nitrous Oxide Emission from Native and Reestablished Prairies in Southern Wisconsin

Presettlement vegetation in southern Wisconsin included areas of oak savanna (Quercus spp.) that supported an understory of prairie vegetation, as well as open prairie. Nitrous oxide emissions from original ecosystems most likely represented the presettlement, terrestrial contribution to atmospheric N20 in the region. Estimates of N20 production by such systems could provide a base level to which relative contributions from managed lands might be compared. Nitrous oxide emissions were monitored by a static chamber technique from three prairie sites in southern Wisconsin from autumn through spring. Two sites were at the Aldo Leopold Memorial Reserve, Sauk County, and the third in Dane County on an outlying property of the University of Wisconsin Arboretum. The sites varied in soil texture (loamy sand and silt loam), vegetational succession (early successional vs. climax), degree of disturbance (native vs. established), and frequency of burning. Nitrous oxide emissions from the three prairie sites were similar and very low over the entire sampling period, ranging from 0.9 ng N20-N m-2s1 to nil. Emissions did not appear to be affected by soil wetting and drying cycles created by rain. Highest N20 fluxes were measured when soil temperatures were warmest, and during initial spring thaw. Coefficients of variation (CV in %o), a measure of spatial variability associated with N20 emissions at each site on a given sampling date, were low and ranged from 7-79% (for flux values above the detection limits, 0. lng N20-N m-2s1). Nitrous oxide emissions from these prairie sites were more than an order of magnitude lower than the range of values reported from N-fertilized agricultural lands in southern Wisconsin and in general were lower than from replanted forests.