Impact of Soil Biochar Applications on Nutrient Leaching.

Soil applications of biochar, a co-product of lignocellulosic bioenergy production using the pyrolysis platform, has been proposed as a potential means of sequestering carbon, improving soil quality and of returning plant nutrients removed from soils by the harvesting of biomass crops.  We used soil columns to investigate the impact of biochar applications and biochar interactions with swine manure on the leaching of NO₃, total P, K, and various trace nutrients during a one-year study.  A total of 48 columns were repacked with 1 kg of Clarion loam, amended with four levels of biochar (0, 5, 10 and 20 g-biochar/kg-soil) and two levels of dried swine manure (0 or 5 g dry manure/kg-soil). The manure was incorporated in the top 3 cm during week 12 of the experiment.  The columns were leached weekly with 200 mL of 0.005 M CaCl₂. Among controls receiving no manure, significantly higher amounts of NO₃ leached from columns amended with 20 g kg^-1 biochar relative to columns containing 0, 5, or 10 g kg^-1 biochar.  This suggests that biochar enhanced mineralization of soil organic matter.  Among columns receiving manure additions, by contrast, 7 to 10% more NO₃ leached from the 0 g kg^-1 biochar columns than the 5, 10 or 20 g kg^-1 biochar columns.  A possible explanation for the observed interaction between biochar treatments and manure additions is that readily mineralizable N-containing organic compounds from the manure were adsorbed and stabilized by the biochar. Biochar additions substantially reduced leaching of total P following manure due to adsorption but increased leaching losses of K due to the additon of K with the biochar.