Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2015
Publication Date: 7/2/2015
Citation: Trippe, K.M., Griffith, S.M., Banowetz, G.M., Whittaker, G.W. 2015. Changes in soil chemistry following wood and grass biochar amendments to an acidic agricultural production soil. Agronomy Journal. 107(4):1440-1446.
Interpretive Summary: The utility of biochars produced by biomass gasification for remediation of acidic production soils and plant growth in general is not as well known compared to effects from biochars resulting from pyrolysis. Our recent characterization of biochars produced from gasification of Kentucky bluegrass (Poa pratensis L.) seed screenings (KB) and wood conifer tree tops suggested that both may have utility in remediation of acid farm soils where crop yield is diminished from aluminum toxicity. We report that both of these gasification biochars raised the pH of these acidic soils, enhanced EC, and contributed plant nutrients to the soil milieu. Accordingly, we conclude both have potential utility in remediating acid soils. Based on other studies, it is likely that their greatest impact on soil quality and plant productivity will occur on soils with reduced CEC and soil organic matter. Their production and sale provide potential added value to operations that generate plant biomass like the feedstocks used in this study. The use of these renewable co-products to produce bioenergy and a marketable biochar product may provide environmental and economic benefits to farming and wood product operations. A better understanding of the characteristics and direct and indirect effects of biochar in soils, and on plant growth, especially in field trials, is needed in order to extend the utility of biochar use in different markets and to develop an estimate of the commercial value. Based on the apparent sorption characteristics of these gasification-derived biochars, it seems likely that other practical uses can be identified, for example as a toxic chemical sorption agent possibly in stormwater remediation. Investigation of alternative uses of biochar was beyond the scope of this study but is being pursued. Selective binding of some ions, including heavy metals and possibly organics, and the capacity to alter acid soil pH could also provide value in acid soil remediation at active and abandoned mine sites where re-vegetation projects are challenged by harsh soil conditions that inhibit plant establishment and growth.
Technical Abstract: The utility of biochars produced by biomass gasification for remediation of acidic production soils and plant growth in general is not as well known compared to effects from biochars resulting from pyrolysis. Recent characterization of biochar produced from gasification of Kentucky bluegrass (Poa pratensis L.) seed screenings (KB) suggested that KB biochar might have utility in remediation of acid farm soils where aluminum uptake limits wheat growth. Farmers routinely use lime to adjust soil pH to minimize Al toxicity and optimize plant nutrient use. Based on the basic pH (>10) of KB biochar, we hypothesized that KB biochar could be used as a “liming” agent and also provide minerals and nutrients for plant growth. A replicated greenhouse pot study was conducted in which single plants of wheat (Triticum aestivum L.) were grown for 74 d in 650 cm3 black plastic pots. Pots contained either a Freeman or Bernhill soil collected from acidic agricultural production fields in Spokane County, WA, U.S.A amended with different percentages of biochars produced by gasification of either KB seed screenings or chipped conifer tree tops. Due to slight differences in the densities of the two biochars, the resulting experimental final mass concentrations of the KB product to soil was 0, 4, 12, 25, and 58 g kg-1 while those used for wood biochar were 0, 7, 17, 37, and 86 g kg-1. The KB biochar was produced in a modified entrained flow gasifier at 650 to 750°C. Wood biochar was produced in a downdraft gasifier at 1100 to 1400°C. Results presented here are the first showing the effects of biochar produced by gasification of KB seed screenings on the growth of wheat. Greenhouse grown wheat, in soil amended with either biochar product, showed a dramatic increase in growth with increasing concentrations. Plant mineral nutrition was significantly enhanced, most likely from adjustment of the acid farm soils to more optimum pH levels but also directly from enriched mineral nutrition offered by the biochars. Addition of either biochar to the soils immobilized soil Al and reduced Al uptake and potential plant Al toxicity observed under acidic soil conditions. Calcium also showed reduced plant uptake and soil immobility with increases in biochar concentration. Selective binding characteristics of the biochars for some ions, heavy metals and possibly organics, along with and the capacity to alter acid soil pH suggest a potential utility in acid soil remediation. This report details the effects of these biochars on soil properties; a companion paper (this issue) describes the impact of both biochars on plant growth observed in these studies.