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Biochar is produced as a by-product of the low temperature pyrolysis of biomass during bioenergy extraction and its incorporation into soil is of global interest as a potential carbon sequestration tool. Biochar influences soil nitrogen transformations and its capacity to take up ammonia is well recognized. Anthropogenic emissions of ammonia need to be mitigated due to negative environmental impacts and economic losses. Here we use an isotope of nitrogen to show that ammonia-N adsorbed by biochar is stable in ambient air, but readily bioavailable when placed in the soil. When biochars, containing adsorbed 15 N labelled ammonia, were incorporated into soil the 15 N recovery by roots averaged 6.8% but ranged from 26.1% to 10.9% in leaf tissue due to differing biochar properties with plant 15 N recovery greater when acidic biochars were used to capture ammonia. Recovery of 15 N as total soil nitrogen (organic+inorganic) ranged from 45% to 29% of 15 N applied. We provide a proof of concept for a synergistic mitigation option where anthropogenic ammonia emissions could be captured using biochar, and made bioavailable in soils, thus leading to nitrogen capture by crops, while simultaneously sequestering carbon in soils.

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Low‐temperature pyrolysis of biomass produces a product known as biochar The incorporation of this material into the soil has been advocated as a C sequestration method. Biochar also has the potential to influence the soil N cycle by altering nitrification rates and by adsorbing or NH3 Biochar can be incorporated into the soil during renovation of intensively managed pasture soils. These managed pastures are a significant source of N2O, a greenhouse gas, produced in ruminant urine patches. We hypothesized that biochar effects on the N cycle could reduce the soil inorganic‐N pool available for N2O‐producing mechanisms. A laboratory study was performed to examine the effect of biochar incorporation into soil (20 Mg ha−1) on N2O‐N and NH3–N fluxes, and inorganic‐N transformations, following the application of bovine urine (760 kg N ha−1). Treatments included controls (soil only and soil plus biochar), and two urine treatments (soil plus urine and soil plus biochar plus urine). Fluxes of N2O from the biochar plus urine treatment were generally higher than from urine alone during the first 30 d, but after 50 d there was no significant difference (P = 0.11) in terms of cumulative N2O‐N emitted as a percentage of the urine N applied during the 53‐d period; however, NH3–N fluxes were enhanced by approximately 3% of the N applied in the biochar plus urine treatment compared with the urine‐only treatment after 17 d. Soil inorganic‐N pools differed between treatments, with higher concentrations in the presence of biochar, indicative of lower rates of nitrification. The inorganic‐N pool available for N2O‐producing mechanisms was not reduced, however, by adding biochar.

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