Roadside soil amendments, like compost and biochar, are used to mitigate the impact of stormwater runoff on the release of pollutants, like nitrogen, to waterways. However, biochar and compost may leach nitrogen and this could be exacerbated by climate change driven increases to storm volume and antecedent dry period (ADP). Despite this, neither amendment has been evaluated under these climate change scenarios. To properly implement these materials, it is crucial to characterize leachate from biochar and compost-amended soils. We compared nitrogen concentrations in outflow from biochar and compost-amended roadside soils following a series of simulated large volume storm events and a series of intermittent storm events with increasing ADPs. First, columns of roadside soil and biochar (30% v/v & 4% w/w) or compost (30% v/v) were irrigated to simulate either 1 yr-6 hr or 5 yr-6 hr storm events for Virginia. Then, columns underwent a series of 5 yr-6 hr storm events with increasing ADPs. Outflow was analyzed for total dissolved nitrogen (TDN). Columns were routinely weighed to gravimetrically track soil moisture. Results indicated that compost amended soils consistently had the highest effluent TDN concentrations in large storm events and increased ADPs. 30% v/v biochar consistently had the lowest effluent TDN concentrations in both storm series. All amendments improved soil moisture with 30% v/v biochar having the most significant effect on soil moisture. These results suggest that 30% v/v biochar may be suitable for use as a roadside soil amendment, especially under these increasingly common climate scenarios.
