INVESTIGATION OF BIOCHAR FOR AMENDMENT OF A DISTURBED URBAN SOIL

We examined the influence of biochar in amending a disturbed urban entisol that is sandy, quartz rich, and very low in organic matter. We assessed short term (2–3 week) plant growth by comparing dry plant mass among varying treatments of biochar and/or inorganic fertilizer and a control. Biochar has been reported to increase water holding capacity, improve retention of soil nutrients, and enhance beneficial microorganism growth. Our hypothesis was that biochar would improve short term growth by enhancing the nutrient and water retention in the high drainage, sandy soil. We tested this with three species in a controlled greenhouse environment and by measuring pH and water retention. The sandy soil had a pH of 6.85 whereas commercial biochar had a pH of 6.40.

Vigna radiata (mung bean) and Avena sativa (common oat) were planted in control (original) sandy soil, soil intermixed with 1%, 3%, 7%, 10%, and 20% (by mass) commercial biochar, the same percentages of biochar with full commercial fertilizer (as recommended), and soil without biochar containing ¼, ½, full, 2x, and 4x the recommended fertilizer dosage. All biochar-only treatments for Mung bean yielded greater above ground biomass than the control, but fertilizer-only and combined biochar-fertilizer treatments were variable relative to the control, while in common oat most fertilizer treatments yielded higher above ground mass than the control whereas biochar treatments were variable. None of these results, however, could be demonstrated to be significant at a 5% confidence level. Brassica rapa (Wisconsin fast plant, standard seed [improved basic, Rbr]) was not tested for fertilizer treatment and showed no significant difference from the control among biochar treatments. Data were suggestive that increasing biochar content correlated with increased water retention, but again this trend could not be demonstrated to be statistically significant. These results suggest that in the early stages of plant growth biochar does not produce significantly different results than fertilizer. This leaves open the possibility that biochar can serve as a lower input, alternative remediation medium in urban soils.