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Title: Switchgrass biochar effects on soil microbial dynamics and wheat yield in two soils from different regions

Author
item KELLY, CHARLENE - Us Geological Survey (USGS)
item Calderon, Francisco
item Acosta-Martinez, Veronica
item Mikha, Maysoon
item Benjamin, Joseph
item RUTHERFORD, DAVIS - Us Geological Survey (USGS)
item ROSTAD, COLLEEN - Us Geological Survey (USGS)

Submitted to: Pedosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2015
Publication Date: 5/6/2015
Publication URL: http://handle.nal.usda.gov/10113/62016
Citation: Kelly, C., Calderon, F.J., Acosta Martinez, V., Mikha, M.M., Benjamin, J.G., Rutherford, D., Rostad, C. 2015. Switchgrass biochar effects on soil microbial dynamics and wheat yield in two soils from different regions. Pedosphere. 25(3): 329–342.

Interpretive Summary: Biochar is the product of heating plant biomass in the absence of oxygen, resulting in a highly carbonized material. Switchgrass is a biomass crop that has gained notoriety in recent times. This research illustrates the effects of switchgrass biochar on soil microbes as well as nitrogen content. This is relevant because biochar has been proposed as a soil amendment that can enhance C sequestration and improve soil quality. However, the effects of the amendment on soil biology has not been studied extensively. Our results show that biochar can affect the amount and kinds of microbes in soil, which in turn could affect the capacity of the soil to cycle nutrients and support plant growth.

Technical Abstract: We assessed microbial activity and community composition of two distinct (clayey) soil types (a Colorado Aridisol (CO) and a Virginia Alfisol (VA) ) following the application of switchgrass (Panicum virgatum) biochar applied at four treatment levels (0, 2.5%, 5%, and 10% w:w) for wheat production (Triticum aestivum) . We measured wheat shoot biomass and N content and selected soil properties including microbial biomass C and N (MBC, MBN) and nitrification rates. The soil microbial community structure was characterized according to fatty acid methyl esters (FAME) profiles. MBC and net nitrification rates decreased in both soils in proportion to an increase in biochar levels, but the effects were more marked in the CO soil (e.g. MBC decreased from 139.4 to 2.1 µg C/g in CO soil and from 906.5 to 580.3 µg C/g soil in VA soil with 10% biochar addition). Biochar additions resulted in slightly increased MBN in the CO soil at the 2.5% biochar level (17.5 to 21.7 mg N/soil), but had no effect on the MBN in VA soil. MBC:MBN ratio declined from 7.9 to 0.5 and from 8.8 to 6.6 in CO and VA soil with 10% biochar addition, respectively; indicating a shift in fungal versus bacterial abundance, especially in the CO soil. Wheat shoot biomass decreased from 17.7 g to 9.1 g with incremental additions of biochar in the CO soil, but was not significantly affected in plants grown in the VA soil. A fatty acid recovery assay indicates that biochar can introduce artifacts in FAME analysis so the results need to be interpreted with caution. Non-corrected total FAME concentration indicate a decline by 45% and 34% with 10% biochar addition in CO and VA soil, respectively; though these differences become non-significant when the correction factor is applied. However, a significant decline in the fungi:bacteria ratio is still evident upon correction in the CO soil with biochar addition. Our results indicate that this switchgrass biochar has the potential to cause short-term negative impacts on plant biomass as well as alter these soils’ microbial community structure.