Impact of Biochar Amendments On the Quality of a Typical Midwestern Agricultural Soil.

Biochar, a co-product of thermochemical conversion of lignocellulosic materials into advanced biofuels, may be used as a soil amendment. We investigated the impact of biochar amendments on the quality of a Clarion soil (Mesic Typic Hapludolls), collected (0-15 cm) in Boone County Iowa. Biochar (<0.5 mm) prepared by slow pyrolysis of mixed hardwood lumber was mixed with field moist soil in a rotary cement mixer to yield 0, 5, 10, and 20 g-biochar kg-1 soil. Repacked soil columns were incubated for 500 days at 25°C and 80% relative humidity. On week 12, 5 g of dried and ground swine manure were incorporated into the upper 3 cm of soil for half of the columns. Once each week, all columns were leached with 200 mL of 0.001 M CaCl2. At the end of the incubation, soil was excavated from the columns (0-3 cm, 3-6 cm, and 6 cm-bottom depths) and analyzed. Soil bulk density increased with time for all columns, and after day 54 bulk density was significantly lower for biochar amended soils relative to the un-amended soils. The biochar amended soils had greater water retention (13 and 10% greater at 1 and 5 bars, respectively), larger specific surface areas (up to 18%), higher cation exchange capacities (CEC increased from 18.1 to 21.7 cmol kg-1) and pH values (up to 1 pH unit) relative to the un-amended controls. No effect of biochar on saturated hydraulic conductivity was detected. The biochar amendments significantly increased total N and organic C by up to 7% and 69%, respectively, and Mehlich III extractable P, K, Mg and Ca but had no effect on Mehlich III extractable S, Cu, and Zn. The results indicate that biochar amendments have the potential to substantially improve the quality and fertility status of Midwestern agricultural soils.