Biochar Increases the Ion Exchange Capacity of Potting Mix

Biochar is organic matter that has been heated in little to no oxygen in a process called pyrolysis.  Biochar’s high surface area is covered with exchange sites that can hold and release the plant nutrient ions, potentially increasing fertilizer efficiency and decreasing leaching. Different amounts of biochar were incorporated into Sunshine mix planting media. The treatments included: 1) a control pot filled with media but without biochar or a plant; 2) a control pot without biochar but with a fibrous begonia plant; 3) 5%; 4) 10%; 5) 15%; 6) 20%; 7) 25%; 8) 30% biochar by volume incorporated into the substrate with a fibrous begonia plant; and 9) a 10% biochar by volume unmixed at the bottom of the pot without a plant. Leachates were collected weekly for 2 months, and the concentrations of ammonium, nitrate and ortho-phosphorus determined. The amount of nitrate, ammonia, and phosphate remaining in the media at the end of the season was measured. The biochar used in this study strongly sorbed both nitrate and ammonia, and a small but statistically significant amount of ortho-phosphate.