Can Biochar Improve Soil Function in an Agroforestry System?: Effects of Nutrient Supply, Microbial Activity, and Greenhouse Gases.

J. Taghavimehr^1,2, M.D. MacKenzie¹

¹Department of Renewable Resources, 442 Earth Science Building, University of Alberta, Edmonton, AB, Canada T6G 2E3

²Corresponding author: Jamal Taghavimehr (jamal2@ualberta.ca)

Short rotation coppice (SRC) systems using willow (Salix spp.) grown on marginal soil, amended with biochar may represent a promising source of renewable green energy for rural areas. The Ohaton Wood Energy project, located in Camrose County, is one of several ongoing SRC projects in Alberta. This project examined nutrient availability, microbial activity and community composition, and greenhouse gas (GHG) emissions in Solonetzic soils after biochar application and wastewater irrigation.  Willow and conifer biochar were used at 1 and 2.5% (w/w) application rates. Plant root simulator probes were used to measure soil nutrient availability. Non-metric multidimensional scaling was used to distinguish differences between nutrient and microbial profiles. The nutrient profiles of conifer 2.5% and willow 1% treatments were significantly different from the control in non-irrigated high EC zone. Chloroform fumigation extraction and alkali trap methods were used to assess soil microbial biomass and respiration. Microbial respiration in the irrigated zone was 3 times more than the non-irrigated zone. It increased by 43 µgC-CO₂/g dry soil/Day with addition of conifer biochar at 2.5%. Microbial biomass carbon and nitrogen didn't change drastically in response to biochar addition. Phospholipid fatty-acid (PLFA) analysis and community level physiological profiling (CLPP) methods were used to examine soil microbial community structure and function. Biochar didn't alter PLFA in any of treated soils compared to control, but conifer 2.5% changed CLPP in both high and low EC soils without irrigation. Photoacoustic multi-gas analyzer was connected to static chambers to measure CO₂ and N₂O emissions from soil in the field. Biochar decreased gas emissions from non-irrigated plots in the first 3 weeks. These results indicate that microbial function can change in a short period of time with addition of biochar, but microbial structure might need more time to show changes.