Plant Nitrogen Uptake From Insect Frass Is Affected by the Nitrification Rate as Revealed by Urease and Nitrification Inhibitors

Abstract

Insect protein production is considered a sustainable alternative to livestock protein which furthermore utilizes waste streams. Its production can have positive but also potentially negative environmental effects, which require evaluation. Frass, the byproduct of insect production, is regarded an efficient organic fertilizer or soil amendment. However, several studies report negative frass effects on plant growth and nitrogen (N) cycling. Therefore, a pot trial was carried out which sought to understand N release from frass and subsequent growth and nutrient uptake of Italian ryegrass. Mealworm frass (MWF) or buffalo worm frass (BFW) was applied at two rates (1.5 and 3% w/w) to a soil-sand mix. To evaluate N release processes, frass was applied alone, with a nitrification inhibitor (NI), a urease inhibitor (UI), or both (NI+UI). Plant N, nutrient uptake and soil inorganic N were measured at the experiment's end. To gauge whether altered N fluxes induced changes in the microbial community, soil microbial biomass, bacterial/archaeal abundances and ergosterol content as a fungal biomarker, were determined. Both frass types and application rates stimulated microbial growth and N mineralization. The 3% rate inhibited seed germination, possibly due to salinity or ammonia toxicity. At the 1.5% rate, both frass types were effective fertilizers. MWF led to higher biomass and nutrient uptake, owing to its higher extractable nutrient concentrations. The 3% rate caused nitrite accumulation in the absence of NI. NI improved plant biomass, nutrient uptake, stimulated archaeal and bacterial abundances and prevented nitrite accumulation. UI reduced N mineralization, showing that a substantial fraction of frass organic N is ureic. UI enhanced fungal contribution to the microbial biomass, revealing the importance of bacteria in frass N mineralization processes when UI is not applied. NI and UI combined, induced greater N release from frass than UI or NI alone. Our study demonstrated the usefulness of NI and UI in studying N release from frass. NI can improve plant N uptake and minimize N losses following frass application, reducing its potentially negative effects. UI can retard N release from frass, allowing its application as a slow-release fertilizer, but should not be used concurrently with NI.

Opportunities and challenges in upcycling agri-food byproducts to generate insect manure (frass): A literature review

“…This suggests that phytotoxicity could be due to oxidizable compounds, such as NH 4 , and/or adsorbable on organic matrices (Hénault-Ethier 2020). Higher concentrations of mealworm frass (3% w/w) were associated with the inhibition of ryegrass seedling germination, possibly due to ammonia or salinity (Watson, Preißing and Wichern 2021).…”

“…BSF frass also seem to be a fast-acting fertilizer, with most N present in an organic form, and a variable ammonia content (Elissen, van der Weide and Gollenbeek 2023). The uptake of frass Nitrogen by plants is affected by the nitrification rate (Watson, Preißing and Wichern 2021). Frass can also affect soil pH, which in turn can influence bacterial activity and bioavailability of nutrients and minerals (Choi and Hassanzadeh 2019).…”

The Impacts of Black Soldier Fly Frass on Nitrogen Availability, Microbial Activities, C Sequestration, and Plant Growth

“…The very limited studies available to date have shown that the application of frass increases yield (Rosmiati et al, 2017;Houben et al, 2020Houben et al, , 2021, activates plant defense responses against abiotic (Poveda, 2021) and biotic stress (Quilliam et al, 2020), and improves soil microbial activities (Gebremikael et al, 2020). On the contrary, few other studies found negative effects of BSF frass and other commercially available frass on soil quality and plant growth, such as phytotoxicity (Alattar et al, 2016;Watson et al, 2021a,b) and excessive nitrite accumulation in soil (Watson et al, 2021a).…”

Fresh aquaculture sludge management with black soldier fly (Hermetia illucens L.) larvae: investigation on bioconversion performances

“…Frass are the secondary material generated by insect-based waste management system. They consist of a nutrient rich material that, whether not correctly handled, may results in an important source of environmental impact 43 , 44 . Current practices include use of the frass as soil conditioner/fertilizer in agriculture.…”