Evaluation of Biochar Quality Utilizing Standard Germination Test.

Understanding the impact of biochar quality on germination and crop growth is critical to the agronomic acceptance of soil biochar applications.  We hypothesize that some fresh biochars may contain phytotoxic compounds that can suppress germination and plant seedling growth. We further hypothesize that aged biochars may adsorb allelopathic compounds released from corn residue.  We tested these hypotheses using six biochars produced from various feedstocks, pyrolysis processes, and temperatures. In the first half of the study, we evaluated percent germination, seedling growth (coleoptile and radicle lengths) of corn (Zea Maize) germinated in fresh biochar extracts, extracts from leached biochar, and nutrient solutions prepared with the same nutrient composition and pH as the biochar extracts. Results showed that extracts from the six biochars had no effect on germination, but had significant effects on seedling growth relative to DI water and nutrient solution controls.  Extracts from two biochars produced by high temperature gasification inhibited seedling growth whereas biochars produced at lower temperatures by both slow and fast pyrolysis had no effect on seeding growth. Leaching of the biochars before preparing the biochar extracts eliminated the negative effects on seedling growth.  The results suggest that leaching and possibly aging of biochar may be an effective means of removing any phytotoxic compounds from fresh biochar.  In the second half of the study, we evaluated the ability of biochar to reduce the allelopathic effect of corn residue.  Germination of corn in extracts of corn residue suppressed radicle growth by 94%, however, equilibration of corn residue extracts with leached biochar for 24 hours prior to initiating the germination test increased radicle length 6 to 12 times relative to the corn residue extract controls. This finding suggests that biochars have the capacity to adsorb allelochemicals present in corn residue extracts.  Germination tests appear to be a reliable procedure to differentiate between effects of different types of biochar on corn seedling growth; however, additional greenhouse and field studies will be required to relate these laboratory tests to corn production systems.