A simple technique to eliminate ethylene emissions from biochar amendment in agriculture

Abstract

Biochars have potential value for greenhouse nurseries as a potting amendment, reducing the need for environmentally costly products currently in use. The onsite manufacture of biochars by pyrolysis of woody waste offers additional greenhouse value as a source of clean heat. However, recent work observed that some biochars may evolve ethylene gas, a plant hormone that has adverse effects on many nursery crops. We hypothesize that suitable post-production handling techniques would eliminate ethylene emissions. We monitored for 6 months ethylene emissions from four fresh biochars made from two feedstocks at two temperatures. We also monitored samples of expanded vermiculite for comparison. We then repeated the same testing on the same batches of biochars after they had been stored in the open for 90 days. Ethylene can affect plant development in greenhouses at concentrations as low as 10 ppb. Biochars sampled that were made from hazelnut shells at 370 °C emitted 161 to 183 μg ethylene kg⁻¹ biochar on the first day of incubation and then tapered down slowly. Hazelnut shell biochars prepared at 620 °C emitted 37 to 43 μg ethylene kg⁻¹ biochar the first day of incubation, but then increased slightly on the second day and did not begin to taper off until after day 14. Biochars made from Douglas fir wastes released small amounts of ethylene beginning on the second day, but ceased doing so after the first week. None of the biochars stored in the open for 90 days following manufacture emitted any ethylene. We conclude that this simple post-production handling technique renders biochars safe for use as nursery and greenhouse potting amendments, possibly replacing environmentally expensive expanded vermiculite and/or peat.