Freeze-thaw effect on soil microbial activity with biochar application in subarctic soils

Sunny M. Castillo
Wed, 22 Apr 2026 17:52:04 PDT

Alaska has limited agricultural production due to extreme climatic conditions and weakly developed soils, which affect productivity. In higher latitudes, freeze-thaw cycles are common and influence soil biology and nutrient dynamics, offering a unique opportunity to investigate the use of soil amendments like biochar to enhance native biota and soil's intrinsic properties. Biochar for this study was produced from locally harvested black spruce (Picea mariana), using a fixed bed pyrolysis unit. The production of biochar was electronically controlled with temperatures kept at 550°C, and residence times manipulated by a mechanical auger, in order to yield five distinct biochar products. Chemical analyses showed differences among the biochar samples, including cation exchange capacity (CEC), micronutrients and pH. To evaluate the influence of each biochar on higher latitude native soils and biota, a response surface model was employed to design a set of experiments that measured CO₂ accumulation during a 15-day freeze -thaw cycle. Microbial activity during this experimental phase was monitored before and after freeze-thaw. Results of this study demonstrated that cultivated soils amended with biochar showed higher microbial activity before and after freeze-thaw. Forest soil on the contrary showed no significant results when amended with biochar. These results on different microbial activity were likely due to the amounts of organic carbon present in each soil type. The study serves as an evaluative tool for determining the impact that biochar may have in subarctic regions of the US that have limited agricultural potential as a result of climatic and native soil conditions.