Can biochar conserve water in Oregon agricultural soils?

Authors: Phillips, Claire; Light, Sarah; Gollany, Hero; Chiu, Stephanie; Wanzek, Thomas; Meyer, Kylie; Trippe, Kristin

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2019
Publication Date: 4/1/2020
Publication URL: https://handle.nal.usda.gov/10113/6783962
Citation: Phillips, C.L., Light, S.E., Gollany, H.T., Chiu, S., Wanzek, T.A., Meyer, K.M., Trippe, K.M. 2020. Can biochar conserve water in Oregon agricultural soils? Soil and Tillage Research. 198. https://doi.org/10.1016/j.still.2019.104525.
DOI: https://doi.org/10.1016/j.still.2019.104525

Interpretive Summary: Rising temperatures and loss of snow pack have resulted in more frequent agricultural drought in the Pacific Northwest (PNW), where dryland and irrigated crops rely on snow melt for water during the growing season. To cope with drought, farmers in the PNW are seeking crop management practices that improve water capture and retention. Biochar is charcoal that is added to soil to improve soil and crop yield. A large number of previous studies in the laboratory have shown that when biochar is added to the soil, it can improve soil water holding capacity and retention, but few studies have determined if these results are also seen in the field. Our objective was to characterize the potential drought benefits of biochar. We used rotary tillage to incorporate two gasified biochars at different amendment rates of 9-36 Mg ha-1 in four locations. Six months after incorporation, using laboratory measurements, we found no benefit from biochar amendment on water content at field capacity in the three of the soil types, but observed a small benefit in the soil with the most sand. We monitored soil water content in the field at two of these sites and found biochar sped up soil drying in the loam soil, and had no impact on soil water content in the sandier soil. These results suggested that biochar incorporation created substantial large spaces between the biochar and soil particles clearly increased water loss in the loam soil type. Caution is needed in using biochar as a drought-adaptation tool in soils that naturally have moderate water storage capacity.

Technical Abstract: Rising temperatures and loss of snow pack have resulted in more frequent agricultural drought in the Pacific Northwest (PNW), necessitating soil management practices that improve water capture and retention. A large number of laboratory studies have shown that biochar amendment can improve soil water holding capacity and retention, but few field studies have evaluated the transferability of these findings. Our objective was to characterize the potential drought benefits of biochar incorporated by tillage into soils with different amounts of sand, silt, and clay. We used rotary tillage to incorporate two biochars at amendment rates of 9-36 Mg ha-1 in four locations. Six months after incorporation, we found no benefit from biochar amendment on water content at field capacity except in the soil with the most sand. We also found a decrease in water content at wilting point in all soil textures. We monitored in situ soil water content at two of these sites and found that soil biochar sped up soil drying in the loam soil, and had no impact on soil water content in the loamy sand soil. These results suggest that biochar incorporation created substantial large porosity between biochar and soil particles, which did not contribute to plant-available water in most of the soil types, and which also clearly sped water loss in the loam soil type. Caution is needed in utilizing biochar as a drought-adaptation tool in intermediate-textured soils that naturally have moderate water storage capacity.