Effects of Biochar Addition On N2O and CO2 Fluxes From Three Agricultural Soils as Related to Water-Filled Pore Space.

A laboratory study was conducted to examine the effect of biochar addition on N₂O and CO₂ emission _{from three agricultural soils during a one-year soil column incubation study. Three rates of biochar 0 (control), 15, and 30 g kg^-1 were applied to Clarion loam, Okoboji silty clay loam, and Harps clay loam. Soil bulk density was measured periodically throughout incubation period whereas N2O and CO2 emissions were measured at the end of the study. Application of biochar significantly decreased soil bulk density for all soils by the end of the study period. During N2O and CO2 measurements, soil columns were first rewetted at 70% water-filled pore space (WFPS) of the control, which resulted in ~10% lower WFPS for columns amended with biochar due to lower soil bulk density and then water was added to achieve 70%WFPS for all columns. Nitrous oxide and CO2 fluxes varied among three soil types with fluxes from Okoboji soil being the greatest. In general, application of biochar enhanced soil respiration and CO2 flux for Harps and Okoboji, but not for Clarion. Nitrous oxide fluxes did not differ among biochar treatments for Clarion and Harps at both levels of WFPS.  For Okoboji rewetted at 70% WFPS of the control (same gravimetric water content for all columns), biochar amendments  resulted in 74% suppression of N2O emissions compared to control, while rewetting all columns to 70% WFPS (same volumetric water content for all colums) resulted in 68% enhancement of N2O flux from the biochar amended columns. While soil bulk density and WFPS significantly influenced N2O flux from soils, changes in aggregate size and arrangement and soil chemical properties due to biochar application likely had an effect on microbial activity and N2O flux.}