All variables described in Appendix S1, detailing statistical analysis, are included or can be easily derived from these datasets. Concentrations This dataset contains time series of concentrations of CO2, CH4, and N2O in static chambers. The data were used to calculate soil fluxes. variables site site where measurements were taken "AARS":Arlington Agricultural Research Station (WI) "KBS": Kellogg Biological Research Station (MI) trt cropping system code, see methods for full details "G1": continuous corn, grown using no-till best management practices "G2","G3","G4": phases of a corn-soybean-canola rotation, using best management practices for each system. all systems below were harvested annually post-frost. Unless noted, they received spring applications of nitrogen fertilizer equivalent to estimated removal rates. "G5": monoculture switchgrass "G6": monoculture miscanthus, replanted 2010 at AARS "G7": mixture of native grasses "G8": hybrid poplar "G9": early successional field "G10": mixture of native prairie species, unfertilized block replicate block, unique for each site date measurement date, 'yyyy-mm-dd' d.min chamber deployment time (minutes) n2o chamber N2O concentration (ppm) co2 chamber N2O concentration (ppm) ch4 chamber N2O concentration (ppm) vol.m3 chamber volume(meter^3) area.m2 soil area within chamber (meter^2) Daily fluxes This dataset contains single-day N2O flux measurements at the plot level and concurrent ancillary measurements of soil properties. These data were used to generate Tables 1-2 and Figures 2-4. Details of flux estimation are given in the paper. variables Unless stated otherwise, variables with the same name as in prior tables have the same interpretation. site trt system largely redundant with trt, exept for G2,G3&G4, where this gives the rotational phase during a given year block date n2o.ha.day N2O flux (g N2O-N per hectare per day) method method used for flux estimation "HMR": nonlinear HM model, as implemented by the HMR package "LR": slope from a linear regression nh4 inorganic nitrogen was measured using resin strips in 2009 and with KCL extractions in 2010-11; ammonium concentration is thus in units of ug N per cm^2 per day in 2009 and ug N per g soil otherwise no3 nitrate concentrations, units are as described above soil.t soil temperature (C) vwc soil volumetric water content wfps soil water-filled pore space wfps.c rescaled ("corrected") wfps, scaled and centered by site Aggregate annual fluxes Daily fluxes were aggregated at the plot level over a calendar year. Details of aggregation are given in the paper. variables site trt system block year flux aggregate annual flux (g N2O-N per hectare per year)