“Nearly 90% of the total biomass of hemp plants grown for CBD is left to rot in piles, burned, or hauled to landfills post-harvest even though these residues are nutrient-rich. Composting is an option for waste management and nutrient recovery for hemp producers. However, materials, labor costs, time, and space needed to properly construct compost piles pose significant logistic challenges to smallholder farmers who want to manage their waste on-farm. Additionally, the high lignin content of cannabis hurd is often poorly degraded if the compost fails to meet national organic standards for thermophilic conditions.” According to recent research, a potentially more efficient and cost-effective alternative is to convert leftover cannabis waste into bio-fertilizers through a semi-anaerobic process by adding microbial inoculants that specialize in lignin degradation.

Imio Technologies has developed cannabis-specific microbial inoculants designed to optimize the conversion of hemp waste into a bio-available form. “Applied as a liquid culture, Imio microbes colonize wasted stalks and produce organic acids and oxidative enzymes that decompose lignin and release plant nutrients. This study aimed to investigate the ability of Imio microbial inoculants to degrade lignin-rich material into a fertilizer substitute,” the researchers say.

Outcompeting indigenous microbes
The results of the study showed high activity of oxidative enzymes produced by Imio and Effective Microorganisms (EM) inoculants, which suggests the added microbes successfully colonized the wasted stalks and initiated lignin degradation. “Despite this trend, there were exceptions where the negative control (water) produced measurable and even higher activities of oxidases than the prototype inoculants. This activity can be attributed partly to the indigenous microbial community arising from the storage of the post-harvest hemp material outdoors in uncontrolled environmental conditions. It is likely that the established microbes were active prior to inoculation, which would explain the observed enzyme production. Regardless, these activities were much less when compared to the other treatments, indicating the commercial inoculants were successful at out-competing indigenous microbes to some degree,” the researchers say.

Nutrient recovery
According to the results, nutrient analyses performed on the microbially treated hemp waste validate that digested hemp C:N ratios and nutrient values are comparable to that of finished composts. “The digested hemp could be used as an organic fertilizer substitute because it yields relatively high amounts of primary and secondary nutrients. The C:N ratio is also desirable from a composting perspective, which ranges from 19–22, indicating the amendment is stable for fertilizer application.”

Despite these generalizations, liquid formulations produced a slightly higher C:N ratio and lower concentrations of primary and secondary nutrients except when compared to bran formulations, which was likely due to the nutritional and physical properties of the wheat bran itself. “The use of bran as a mode of delivery would provide additional nutrients to the hemp waste and lower the C:N ratio of the resulting fertilizer. This would explain the improved fertility properties of the recycled biomass generated from bran formulations when compared to liquid. Regardless of delivery mode or microbial treatment, amending field soil with digested hemp improved soil fertility, %OM, and pH.”

Phytotoxicity is common in immature composts and bokashi fertilizers that have not been properly cured. “In this study, longer cure phases correlated with increased germination rates of both plant species, suggesting that uncured digested hemp was phytotoxic to a certain extent and the cure phase is necessary to reduce deleterious effects. Our experiments suggest a 2-week cure phase seemed to be sufficient in reducing phytotoxicity, which is consistent with the general recommendations for curing bokashi composts. When properly cured, the digested hemp fertilizer can provide additional benefits to the soil such as improving its physical properties.”

Disease suppression
“Because there is only one pesticide currently approved for use on cannabis plants in the US, pathogen suppression by the digested hemp fertilizer would represent an innovative value-add to farmers who employ the Imio recycling strategy,” the researchers say. Plate competition assay results indicate that cured material was more suppressive against fungal pathogen growth than uncured material. This suggests that the curing phase is not only necessary to reduce phytotoxic effects but also to stabilize decomposition processes and inhibit disease. “Other researchers have reported that the level of decomposition of organic material is related to its antagonistic effects against R. solani, with more decomposed material generally being more effective at controlling pathogen growth. Despite these findings, even the hemp waste treated with water (negative control) suppressed the growth of R. solani, comparable to the other treatments. This result indicates that decomposing hemp, in general, could be used as a method to control certain soilborne pathogens regardless of microbial treatment.”

Read the full study at: www.tandfonline.com