Biochar Source Interaction with Medicago Truncatula Genotypes Differing in Ethylene Sensitivity.

Biochar properties depend on pyrolysis process and feedstock source and may include potentially physiologically active compounds such as ethylene and polyaromatic hydrocarbons. “Wild” and “sickle” (an ethylene insensitive mutant) genotypes of Medicago truncatula (barrel clover) were used to evaluate the effect of selected biochars on nodule formation and root morphology in a greenhouse study. Four biochars developed from two feedstocks, switchgrass (Panicum virgatum L.) and corn stover (Zea mays) produced using two methods of pyrolysis (fast and slow) were examined.  Biochar treatments at a 1% application rate increased nodule formation and plant biomass across all genotypes. The lack of inhibition by biochar on nodule formation in the “wild” genotype suggests that biochar did not increase ethylene concentration within the plant root to physiologically significant levels. However biochar increased root length of lower order lateral roots (0-1 mm diameter) by 40% compared to the control in the “wild” but not in the “sickle” genotype. There was a significant difference in plant response associated with biochar source. Fast pyrolysis biochar produced from corn stover resulted in the greatest increase in plant dry weight, root surface area, and root volume. These results suggest that generic biochar applications in crop production systems are not likely to produce easily predictable results across a range of field environments and agronomic practices. Further research is needed in order to elucidate mechanisms associated with biochar-microbe-plant interactions.