Insect frass composition and potential use as an organic fertilizer in circular economies

Authors: AMORIM, HELEN - University Of Arkansas; Ashworth, Amanda; Arsi, Komala; Rojas, Maria - Guadalupe; Morales Ramos, Juan; Donoghue, Ann - Annie; Robinson, Kelsy

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2023
Publication Date: 1/3/2024
Citation: Amorim, H., Ashworth, A.J., Arsi, K., Rojas, M.G., Morales Ramos, J.A., Donoghue, A.M., Robinson, K. 2024. Insect frass composition and potential use as an organic fertilizer in circular economies. Journal of Economic Entomology. Article toad234. https://doi.org/10.1093/jee/toad234.
DOI: https://doi.org/10.1093/jee/toad234

Interpretive Summary: Insect farms are expanding worldwide in response to growing demands for sustainable protein sources for both animal feed and human consumption. Insect rearing, also called a "mini livestock", needs less land and water and can utilize food waste as feed, which can reduce production costs and help lessen the negative impacts of landfills on the environment. The insect excreta or "frass" contains nutrients that can help boost soil health and benefit crop production. To date, few researchers have investigated the properties of this novel, value added manure. Thus, in the present study, scientists analyzed the chemical composition and presence of pathogens in insect frass compared to poultry litter, one of the most common nutrient sources used in agriculture. They found that insect frass had approximately 2 times more carbon and nitrogen, similar phosphorus levels, and virtually no toxic elements compared to poultry litter. In turn, poultry litter had more potassium, calcium, and micronutrients (nutrients that plants require in small amounts). Scientists argued that the different chemical properties and presence of pathogens are related to the feed and supplements used in the insect and poultry production systems, and concluded that insect frass is a promising, eco-friendly novel nutrient source. Moving forward, researchers plan to feed insects with different diets, and mix insect frass with other fertilizer sources (e.g., poultry litter and mineral fertilizers) to develop a more enriched, cheaper, and cleaner fertilizer, as well as conduct field experiments to evaluate the impacts of insect frass applications on soil health and crop yield and nutrition.

Technical Abstract: Insect manure or “frass” has emerged as an alternative nutrient source to alleviate the dependence on mineral fertilizers, reduce food waste, and promote food security. Yet, research on insect frass chemical composition is in its infancy. Here, we assessed the chemical properties of yellow mealworm (Tenebrio molitor L.) frass compared to poultry litter (PL). Insect frass was obtained from the National Biological Control Laboratory (NBCL; IF-L) and from an insect rearing company (IF-C). Poultry litter was collected from facilities in Arkansas (PL-AR) and North Carolina (PL-NC). Samples were analyzed for pH, electrical conductivity (EC), macro- and micronutrients, potentially toxic elements, pathogens, and indicator microorganisms. On average, insect frass had 43 and 47% higher C and N than PL, respectively (p < 0.05). Considering a 5 Mg ha-1 application rate, IF-C can supply 159 kg N ha-1, twice the N supply of PL-AR (78 kg ha-1). IF-L had a 53% higher P supply than PL-NC. Mean K, Ca, S, and micronutrient contents were higher in PL than frass (p < 0.05), whereas As, Cd, Cr, and Pb were nearly absent in frass. Chemical composition and pathogens in fertilizer sources are largely affected by insect rearing substrate and supplements used in poultry and insect production. Insect frass utilized in this study had optimum C and N rates relative to PL, suggesting a promising soil amendment for improving soil health and C sequestration, thus contributing to sustainable agricultural intensification and mitigation of food waste in circular economies.