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Through meta‐analysis, we synthesize results from field studies on the effect of biochar application on N2O emissions and crop yield. We aimed to better constrain the effect of biochar on N2O emissions under field conditions, identify significant predictor variables, assess potential synergies and tradeoffs between N2O mitigation and yield, and discuss knowledge gaps. The response ratios for yield and N2O emissions were weighted by one of two functions: (i) the inverse of the pooled variance or (ii) the inverse of number of observations per field site. Significant emission reductions were observed when weighting by the inverse of the pooled variance (−18.1 to −7.1%) but not when weighting by the number of observations per site (−17.1 to +0.8%), thus revealing a bias in the existing data by sites with more observations. Mean yield increased by 1.7 to 13.8%. Our study shows yield benefits but no robust evidence for N2O emission reductions by biochar under field conditions. When weighted by the inverse of the number of observations per site, N2O emission reductions were not significantly affected by cropping system, biochar properties of feedstock, pyrolysis temperature, surface area, pH, ash content, application rate, or site characteristics of N rate, N form, or soil pH. Uneven coverage in the range of these predictor variables likely underlies the failure to detect effects. We discuss the need for future biochar field studies to investigate effects of fertilizer N form, sustained and biologically relevant changes in soil moisture, multiple biochars per site, and time since biochar application. Biochar reduced mean N2O emissions by 12.4% when weighted by the inverse of the pooled variance.Biochar did not significantly reduce N2O emissions when weighted by the inverse of the number of observations per site.The effect of weighting function suggests site‐dependence and dataset limitations on the potential of biochar to mitigate N2O.Biochar increased yield for both weighting functions.

Manure generated by intensive livestock operations poses potential ecological risk in the form of water pollution and greenhouse gas emission. To assess the impact of biochar on coarse‐textured soils under contrasting nutrient management regimes, a 55‐d incubation was conducted using unplanted soil columns amended with manure, slurry, or fertilizer (plus unamended control), each with or without biochar applied at 2% soil mass (dry weight basis). Under repeated leaching, the cumulative N2O emission from the columns was significantly affected by the presence of biochar (p< 0.0001), although these data were not normally distributed. Results indicated that the biochar‐amended soils emitted significantly less N2O than their unamended counterparts, with the exception of manure‐amended soils. The presence of biochar increased the pH of column leachate by 0.08 to 1.70 and significantly decreased the cumulative amount of mineral N leached from the soil. The presence of biochar significantly increased the amount of PO43−–P in soil leachate, but there was no significant difference between the means for any of the amendments used on their own relative to their biochar‐amended counterparts. The data demonstrate that biochar could potentially aid in the mitigation of N2O emissions from certain soils and in N loss in leachate from soil amended with slurry, manure, or fertilizer used in livestock systems.