Biochar applications to boreal podzol improve soil hydraulic properties and control nitrogen dynamics

The study aimed to investigate the effects of biochar (BC) application on hydraulic properties and resulting nitrogen (N) transport in a podzolic soil profile. Soil samples were collected from an agricultural research field in Pasadena, Newfoundland, Canada. Three types of leaching columns were prepared: (1) topsoil, (2) top and E-horizon soil, and (3) mixed soil (2:1 ratio of topsoil and E-horizon soil). Granular biochar (GBC) and powder biochar (PBC) were mixed with soils at the rate of 0%, 1% and 2% (w/w). BC's morphological structure and pore size distribution were examined using a scanning electron microscope, and the specific surface area was assessed by the Brunauer−Emmett−Teller method. Soil physical and hydraulic properties (bulk density, porosity, field capacity (FC), permanent wilting point (PWP), plant available water (PAW)), leaching concentration of nitrate (NO3-) and ammonium (NH4+), and volume of leachate were measured through a total of 378 experiments under laboratory conditions. GBC and PBC showed hydrophobic and hydrophilic characteristics, respectively. With the 2% PBC amendment, porosity increased by 2.8%, FC by 10%, and PAW by 12.9% in the mixed soil and reduced NO3- leaching by 36% in top & E-horizon soil and NH4+ leaching by 72% in mixed soil. On the other hand, NO3- and NH4+ leaching was reduced by 26% and 33% in mixed soil when treated with 2% GBC. A 2% application rate of both BC (GBC and PBC) showed the best performance to enhance soil hydraulic properties and retain significant amounts of NO3- and NH4+ in the boreal podzol.