Charcoal and Boron Availability.

Charcoal, one form of black carbon, has recently been proposed as a soil amendment to create a more favorable soil environment by improving soil pH in acidic soils, raising the cation exchange capacity in coarse textured-soils and improving nutrient retention and availability in strongly weathered soils. We conducted a series of greenhouse experiments involving acid soil horizons from an Ultisol amended with various rates of biochar. Common bean (Phaseolus vulgaris L. var 'contender') was grown using a completely randomized design and harvested when the untreated check had three fully developed trifoliolate leaves. Plants grown in biochar amended soils showed symptoms indicating boron toxicity and soil characterization showed elevated boron concentrations. Biochar amended samples also showed elevated soil and plant calcium concentrations. We conclude that biochar amended soils need to be asseyed for boron to alleviate the potential for boron accumulation.