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Title: The incorporation of biochar carbon into stable soil aggregates: the role of clay mineralogy and other soil characteristics

item KELLY, CHARLENE - Western Carolina University
item Benjamin, Joseph
item Calderon, Francisco
item Mikha, Maysoon
item RUTHERFORD, DAVID - Us Geological Survey (USGS)
item ROSTAD, COLLEEN - Us Geological Survey (USGS)

Submitted to: Pedosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2016
Publication Date: 8/1/2017
Citation: Kelly, C., Benjamin, J.G., Calderon, F.J., Mikha, M.M., Rutherford, D., Rostad, C. 2017. The incorporation of biochar carbon into stable soil aggregates: the role of clay mineralogy and other soil characteristics. Pedosphere. 27(4):694-704.

Interpretive Summary: In this study, we investigated how biochar can affect soil structure when added to soil under wheat production. Two soils were evaluated, a soil from Virginia, and a soil from Colorado, both high in clay content. Our results indicate that biochar did not improve soil agggregation or water holding capacity in the Colorado soil. The soil from Virginia did see an improvement in the larger sized aggregates with the biochar addition. This suggests that the type of clay present in the soil plays a role in the soil structure benefits from biochar deployment.

Technical Abstract: Biochar amendments may alter soil function and fertility in various ways, including through induced changes in soil structure and aggregate stability. We assessed soil aggregate class fractions and the incorporation of carbon (C) into stable aggregates in two distinct soil types, an Aridisol from Colorado (CO) in the U.S. Central Great Plains dominated by 2:1 clays, and an Alfisol from Virginia (VA) in the southeastern U.S. containing more weathered mixed 1:1 and 2:1 mineralogy, following the application of switchgrass (Panicum virgatum) biochar. The switchgrass biochar was applied at four levels, 0%, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha-1, respectively, to the soil grown with wheat (Triticum aestivum) in an eight-week growth chamber experiment. We also measured changes in soil strength and water-holding capacity using water release curves. In the CO soil, decreases in the amount of aggregates occurring in the 1000-2000, 500-1000, and 250-500 µm size fractions with increasing biochar addition were documented, with concomitant increases in the 53-250 and <53 µm fractions. No changes in aggregate size fractions occurred in the VA soil. In the CO soil, C content increased only in size fractions <1000 µm, with the greatest increases occurring in the 53-250 and <53 µm fractions (>400 and 250% at 10% biochar, respectively). In VA soil, C content within aggregate size fractions increased incrementally with biochar level for each size fraction except the >2000 µm fraction. Given the size fractions of the original biochar, these results indicate that C was incorporated into larger aggregates in the VA soil through organo-mineral interactions. Biochar remained largely unassociated to soil particles in the CO soil, likely as a result of a decline in plant and microbial byproducts imperative to aggregation in 2:1 clay soils. Biochar addition had no significant effects on water-holding capacity or strength measurements in either soil. Our results suggest that adding biochar to more weathered soils (more 1:1 clays) may result in greater stabilization of the incorporated C and may result in less loss due to erosion and transport relative to soils dominated by 2:1 clays.