Preliminary evaluation of a decision support tool for biochar amendment

Authors: Phillips, Claire; LIGHT, SARAH - University Of California - Cooperative Extension Service; LINDSLEY, ADAM - Oregon State University; WANZEK, THOMAS - Oregon State University; Meyer, Kylie; Trippe, Kristin

Submitted to: Biochar
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2020
Publication Date: 2/19/2020
Citation: Phillips, C.L., Light, S.E., Lindsley, A., Wanzek, T.A., Meyer, K.M., Trippe, K.M. 2020. Preliminary evaluation of a decision support tool for biochar amendment. Biochar. 2:93-105. https://doi.org/10.1007/s42773-020-00037-3.
DOI: https://doi.org/10.1007/s42773-020-00037-3

Interpretive Summary: A decision-support tool was developed that enables users to determine an appropriate type of biochar and application rate for their soil and crop system, and that helps identify situations when biochar application may improve crop yields. The tool was developed for the Pacific Northwest of the United States, and uses soil test values to identify soil deficiencies, university extension guidelines to determine fertilizer and liming requirements for different crops, and biochar test values to determine the quantities of nutrients and lime equivalents that can be provisioned by biochar. A greenhouse trial of winter wheat grown in six different soil types with two different biochars was used to evaluate the effectiveness of the tool. The trial demonstrated that the amounts of biochar recommended by the tool were on average 25% too high for ameliorating soil acidity, but that the tool's predictions of soil potassium increases were accurate in all soil types, and its predictions of soil phosphorous increases were accurate in sandy soils. The tool identified one of the soil types as having very low pH for growth of winter wheat, and a second soil type as having marginally low pH and soil phosphorous. The biochar amendment rates recommended by the tool to ameliorate these deficiencies significantly increased wheat growth in the very deficient soil, but not in the marginally deficient soil. In addition, biochar did not improve plant growth in soils with optimal pH and soil nutrient concentrations, which supports to the idea that the liming and fertility aspects of biochar are key to improve yield. This study shows that accounting for readily-measurable fertility and liming properties of biochars can help to predict potential growth benefits in the season following application.

Technical Abstract: Biochar has the potential to improve soil fertility, raise pH, and increase the long-lived carbon content of soil. However, meta-analyses have suggested that only about half of biochar addition studies have demonstrated improved plant growth. Here we describe a decision support tool (DST) for selecting a biochar type and amendment rate to meet soil and crop management goals, based on soil and biochar tests values and crop requirements as reported by regional extension fertilizer and liming recommendations. We assessed whether this approach could predict changes in soil chemistry and whether it could identify soils in which amendment would increase yield, using data from a greenhouse wheat trial. The greenhouse data indicated that the DST could provide semi-quantitative predictions of biochar amendment rates needed to meet target soil pH levels, with recommended rates averaging 25% higher than were needed. The DST was better at predicting biochar application rates to provision P and K. Across six soil types, post-harvest measurements of extractable-K showed an average 104% recovery of the quantities estimated to be provisioned by conifer wood or wheat straw biochars. Extractable-P recovery averaged 101% in two sandy soils with low P-retention, but was considerably lower in four soils with higher P-retention capacity. Greenhouse data also showed that wheat growth improved only when biochar alleviated pH that was substantially below critical thresholds for plant growth, and supported the principle of using crop-specific fertility and pH requirements as part of an approach for biochar decision-support.