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Article

Investigating Black Soldier Fly Larval (Hermetia illucens) Frass Applications as a Partial Peat Replacement and Liquid Fertilizer in Brassicaceae Crop Production

by
Maria Y. Chavez
1,*,
Armando Villa Ignacio
2,
Joshua K. Craver
2 and
Jennifer Bousselot
2
1
Department of Plant and Environmental Sciences, New Mexico State University Agricultural Science Center, Farmington, NM 87401, USA
2
Department of Horticulture and Landscape Architecture, Colorado State University, Fort Collins, CO 80526, USA
*
Author to whom correspondence should be addressed.
Agrochemicals 2025, 4(2), 8; https://doi.org/10.3390/agrochemicals4020008
Submission received: 31 January 2025 / Revised: 2 April 2025 / Accepted: 19 May 2025 / Published: 29 May 2025
(This article belongs to the Section Fertilizers and Soil Improvement Agents)
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Abstract

:
Insect frass is the left-over side stream from mass rearing insects as food and feed. Research indicates that black soldier fly, Hermetia illucens, larvae (BSFL) frass can improve the yield of leafy greens while also increasing nutrient uptake. Two studies evaluated the impact of BSFL frass on two Brassicaceae crops: kale (Brassica oleracea) and mustard (Sinapis alba). In Study 1, greenhouse potting mixes comprised of 10% BSFL frass produced kale and mustard fresh and dry weights, relative chlorophyll concentrations, and nitrogen concentration in plant tissues that were comparable to a 100% peat mix control. In mustard tissue, phosphorus and potassium concentrations were higher in the BSFL 10% treatment compared to the control. This provides further motive for incorporating frass into peat-based substrates to reduce peat consumption and extraction. In Study 2, Liquid BSFL frass tea was applied to kale in an outdoor container study. The frass tea only treatment produced the worst outcomes for yield. However, a mixture of frass tea and traditional fertilizer resulted in comparable yield to a control provided the same volume in solely fertilizer. With further research, frass tea could be supplemented to reduce conventional fertilizers.

1. Introduction

Growing insects for food and feed presents an interesting opportunity to redirect waste from other producers and minimize gaps in a circular economy model [1]. Waste serves as feed for the larvae and the excrement, or frass, is a bio-enriched substrate or additive suitable for horticultural crop production [2]. Frass can be used for peat replacement or fertility applications in specialty food crop production [2].
Black soldier fly larvae (BSFL), Hermetia illucens, (Diptera: Stratiomyidae) are high in protein [3] and efficient in reducing waste, reducing dry matter by up to 50% [4]. Therefore, BSFL frass, specifically, has the potential to utilize agriculturally valuable nutrients from existing waste streams and reduce inorganic fertilizer application during crop production [5].
Other studies have found that at low concentrations in a peat-based substrate, 10-20% frass can have positive impacts on lettuce, arugula, tomato, basil, and ryegrass [6,7,8,9]. Although these prior studies have been conducted to investigate the uses of BSFL frass as a peat replacement in horticultural production, they do not address how the incorporation of frass may impact nutrient loss or flux through the system.
When introduced to new environments, frass may influence soil and substrate decomposition and fertility by altering soil properties and introducing new microbes [10,11,12,13]. These impacts may vary based on the type of frass applied or the additional steps taken by insect producers to improve their frass products, such as liquid frass applications. Compost tea is an organic, aqueous product formed from the fermentation of solid compost. The fermentation process can decrease the antagonistic microbes and increase the beneficial microbes. Compost tea applications are notable for stimulating an induced systemic response [14], which may increase a plants’ ability to defend themselves against pathogens.
Kale (Brassica oleracea) is a common crop in the PNW because of its tolerance for colder temperatures and yellow mustard (Sinapis alba) is a common cover crop used in rotation during fall plantings. While some studies have examined the impacts of granular frass on kale [15,16,17], studies have not yet considered a partial replacement for peat or a liquid frass for kale production. Additionally, insect frass has been utilized in ‘field mustard’ (Brassica rapa) [18] and ‘black mustard’ (Brassica nigra) [19] production, but it has not yet been studied in ‘yellow’/’white’ mustard (Sinapis alba) or other cover crops.
Based on past studies [20] it is possible that frass that has additional steps of bioconversion, or fermentation, can result in positive or neutral outcomes for plant productivity. However, more studies are needed to evaluate the best practices for liquid frass application.

2. Materials and Methods

The objectives of this two part study were to (1) determine an effective frass to peat ratio as an alternative substrate for the production of kale and mustard in a greenhouse environment; and (2) evaluate the impacts of a liquid frass product, or tea, on kale growth and production.
Study 1 Frass amended soilless substrate: Kale ‘Winterbor’ and yellow mustard seeds were sown on 2 April 2024. Seedlings were transplanted on 17 May 2024, into 500 mL pots using varying ratios of a commercial peat mix comprised of (by vol.) 85% sphagnum peat and 15% perlite (Greenhouse Potting Soil, Plantorium Greenhouse and Nursery, Fort Collins, CO, USA) and BSFL frass (Chapul Farms, LLC, McMinnville, OR, USA). Three treatments of different peat mix to BSFL frass mixtures, and a 100% peat mix control were established for this experiment (Table 1).
An analysis of the BSFL frass was conducted by the CSU Soil, Water, and Plant Testing Lab (Denver, CO) (Table 2). Pots were placed in a common greenhouse environment at the Colorado State University (CSU) Horticulture Center (Fort Collins, CO, USA) with an air temperature set point of 21 °C. Plants were irrigated as needed using a water soluble fertilizer with a concentration of 0.65 g∙L−1 (All-purpose Miracle-Gro 24N–6P–18K, The Scotts Company LLC, Marysville, OH, USA).
Ten replicates per treatment and species were evaluated for this experiment. Plants were harvested 38 days after transplant on 24 June 2024. Leachate samples were collected from 5 replicates of each treatment prior to harvest using a standard pour through analysis as described in Camberato et al. (2009) [21] and sent to the CSU Spur Soil, Water, and Plant Testing Lab for chemical analysis. Plant size at harvest (PSH) was determined by measuring the height (H; cm), width at the widest point (W1; cm), and width perpendicular to W1 (W2; cm), and calculated using Equation (1).
(W1 + W2 + H)/3 = PSH
Chlorophyll concentration was collected on the most recently fully expanded leaf for each plant using a handheld meter (atLEAFCHL BLUE, atLEAF, Wilmington, DE, USA). Values were converted to SPAD units and then mg/cm2 using an online conversion tool “https://www.atleaf.com/SPAD (accessed on 1 November 2024)”.
Fresh weight (FW; g) of all vegetative biomass was collected and weighed using a balance (Mettler Toledo, Denver, CO, USA). Roots were separated from the growing media by washing with water, and both root and vegetative plant material were dried in a forced air oven (Heratherm, Thermo Fisher Scientific, Waltham, MA, USA) maintained at 70 °C for 72 h prior to determining shoot (SDW; g) and root dry weight (RDW; g). Five representative samples of dried kale tissue from each treatment were further analyzed by the CSU Spur Soil, Water, and Plant Testing Lab to determine macro- and micronutrient content.
Statistical Analysis. Statistical analysis was conducted using JMP®, Pro 16 (SAS Institute Inc., Cary, NC, USA, 1989–2022). Percent data was converted to proportions and transformed with the logit function before analysis. To evaluate, the Anderson-Darling test for normality and Levene’s test for equal variance were conducted to determine if the assumptions for an ANOVA were met. An alpha threshold of p < 0.05 indicates statistical significance. Tukey HD pair wise comparisons were conducted to assess and test for post hoc differences between treatments.
Study 2 Frass tea fertilizer applications: Since this study was meant to explore the use of fertilizer applications for production purposes, only the vegetable crop from Study 1 was selected to investigate in Study 2. Kale ‘Winterbor’ seedlings were sown in 50-cell trays on 24 June 2024 and transplanted into 500 mL pots using a commercial peat mix (Greenhouse Potting Soil, Plantorium Greenhouse and Nursery, Fort Collins, CO, USA) on 6 August 2024. Pots were placed in an outdoor environment with a mean ± SD air temperature and relative humidity of 22.91 ± 5.50 °C and 48.57 ± 22.37%, respectively, monitored using a data logger (Onset HOBO, Bourne, MA, USA). Plants received one of three fertilizer treatments applied weekly (Table 3), with 10 replicates per treatment.
Using the same BSFL frass as Study 1, fresh BSFL frass tea (FT) was brewed aerobically each week in a living soil tea brewer (Rocky Mountain Soil Stewardship, Fort Collins, CO, USA). An aeration system comprised of one motor and two hoses was placed at the bottom of an 18.93 L container, filled with 11.36 L of water. The aeration system was operated for thirty minutes to remove any remnant chlorine from the tap water. One L of frass was wrapped in cheese cloth and suspended in the water. The container was covered, and the tea brewer was left to run for 24 h. After 24 h it was then applied as a liquid fertilizer directly onto the soil surface. A water soluble fertilizer with a concentration of 3.74 g∙L−1 (All-purpose Miracle-Gro 24N–6P–18K) served as the inorganic fertilizer control.
Plants were harvested 30 days after transplant on September 5, 2024. Data collection methods were similar to Study 1 and included PSH, chlorophyll concentration, FW, SDW, and RDW. Additionally, percent dry weight (%DW) was determined from SDW and FW, and calculated using Equation (2).
(SDW/FW) × 100 = %DW
Root to shoot ratio (R:S) was determined from RDW and SDW and calculated using Equation (3).
RDW/SDW = R:S
Statistical design and analysis were similar to Study 1 and described previously.

3. Results

3.1. Study 1 Frass Amended Soilless Substrate

3.1.1. Plant Growth Characteristics and Other Parameters

Plant size at harvest (Figure 1a) was the lowest in BSFL 30% treatment for both crops. In kale, PSH was similar between the control, BSFL 10%, and BSFL 20%; while in mustard, PSH was smaller for BSFL 20% compared to BSFL 10% and the control.
Fresh weight (Figure 1b) of kale (p ≤ 0.0001) and mustard (p ≤ 0.0001) were highest in the control and BSFL 10% treatment and lowest in the BSFL 30% treatment (Figure 1b). Fresh weight for the BSFL 20% treatment was comparable to BSFL 30% treatment in mustard, but this was not the case in kale.
Shoot dry weight (Figure 1c) of kale (p ≤ 0.0001) and mustard (p ≤ 0.0001) were the highest in the control and BSFL 10% and lowest in the BSFL 30%. Shoot dry weight for BSFL 20% was similar to BSFL 30% in mustard, but this was not the case in kale.
No difference in chlorophyll concentration (Figure 1d) among treatments was observed in kale (p = 0.56); while in mustard, a higher chlorophyll concentration was observed under BSFL 10% compared to BSFL 20% and BSFL 30% (p ≤ 0.0001). Chlorophyll concentration was comparable for the control and BSFL 10% in mustard.
There was limited root growth in the BSFL 30% treatment, resulting in undetectable RDW values. Thus, RDW under BSFL 30% for both species is not included for this analysis. Root dry weight (Figure 1e) was lowest under BSFL 20%, with no difference between the control and BSFL 10% observed for both kale (p = 0.003) and mustard (p ≤ 0.0001).
Due to limited FW for BSFL 30% in both species and BSFL 20% in mustard, leachate samples were unable to be collected and have been removed from this analysis. Nitrates (Figure 1f) from leachate samples were lowest in the control for kale (p = 0.008) and mustard (p = 0.02). For kale, nitrates in BSFL 10% were similar to the control, while BSFL 20% produced the highest concentration of nitrates found in the leachate. For mustard, higher nitrate concentrations were observed in BSFL 10% compared to the control. While the concentration of ammonium was also chemically analyzed, detection in samples was limited and the limited values excluded from this analysis.

3.1.2. Macronutrient Concentrations

Similar to leachate samples, limited FW for BSFL 30% in both species and BSFL 20% in mustard prevented their inclusion for macro- and micronutrient analysis. For kale, N (p = 0.25), P (p = 0.79), S (p = 0.26), Ca (p = 0.06), and Mg (p = 0.78) concentrations (Table 4) were mostly similar between the control, BSFL 10%, and BSFL 20%. However, K (p = 0.01) was highest in the control and lowest in BSFL 20%, while BSFL 10% was similar to both. For mustard, N (p = 0.20), S (p = 0.36), and Mg (p = 0.61) concentrations (Table 4) were similar between the control and BSFL 10%, while P (p = 0.03) and K (p = 0.0004) were highest in BSFL 10% compared to the control. However, Ca (p = 0.01) was higher in the control compared to BSFL 10% for mustard.

3.1.3. Micronutrient Concentrations

For kale, B (; p = 0.65), Cu (p = 0.11), Mn (p = 0.40), and Mo (p = 0.13) concentrations (Table 5) were similar between the control, BSFL 10%, and BSFL 20%, while Na (p < 0.0001) was higher in BSFL 10% and BSFL 20% compared to the control. The concentration of Zn (p = 0.025) and Fe (p = 0.04) was higher in the control compared to BSFL 20% and BSFL 10%, respectively. For mustard, B (p = 0.36), Cu (p = 0.49), Fe (p = 0.15), Mn (p = 0.76), Zn (p = 0.24), and Mo (p = 0.30) concentrations (Table 5) were similar between the control and BSFL 10%. Na (p ≤ 0.0001) was higher in BSFL 10% compared to the control for mustard.

3.2. Study 2 Frass Tea Fertilizer Applications

Plant size at harvest (p = 0.90), DW (p = 0.58), and chlorophyll concentration (p = 0.0004) were similar for all treatments (Figure 2a,c,e). While FW was lowest in the FT treatment, the FT + MG treatment produced comparable yield to the MG control (p = 0.04) (Figure 2b). Percent dry weight (p ≤ 0.0001), RDW (p = 0.003), and R:S (p = 0.0004) were higher in the FT treatment compared to the FT + MG and MG treatments (Figure 2d,f,g).

4. Discussion

4.1. Study 1 Frass Amended Potting Media

In other studies, BSFL frass has been applied to kale as a partial and complete fertilizer and compared to a conventional fertilizer control. Fresh weight (yield) and chlorophyll (SPAD) were highest in the 100% BSFL frass treatment and statistically comparable to the control [16,17]. Trends in our results for PSH, FW, SDW, and RDW were similar for both species. The control was statistically comparable to the BSFL 10% treatment, both of which were generally higher than the BSFL 20% and 30% treatments. Root weight is an effective predictor for shoot weight [22], so it’s likely the increased root growth in the lower frass treatments and control resulted in positive outcomes for above ground biomass in those same treatments. Clearly a threshold exists for crop tolerance of insect frass as a potting media and this threshold varies per species. These results are consistent with observations in studies with tomato plants and seedlings grown in BSFL frass [7,23].
Leaf tissue concentrations of both P and K were higher in the BSFL 10% treatment compared to the control for mustard. Mustard is a cover crop known for its ability to remove nutrients from the soil and prevent nutrient leaching [24]. The additional P and K from the provided frass treatments may have been more accessible to mustard given this trait. Kale exhibited the opposite trend, where the control had the highest leaf tissue concentration of K and the BSFL 20% treatment had the lowest. Root production is a primary factor in determining nutrient availability and uptake [22]. For kale, RDW was lowest under the BSFL 20% treatment, which mirrored the reduction in leaf issue concentration of K. Thus, it is likely that as RDW decreased, so did nutrient uptake of K to the plant tissue. S, Mg, B, Cu, Mn, and Mo concentrations in both species’ tissues were not significantly different across treatments and control. However, other studies observed increases in Mg and Mn concentrations in kale tissue in both frass treatments compared to the control [17]. So, the nutrients in our frass may not have been high enough to increase availability to the crops for uptake.
There were no differences in relative chlorophyll concentration for kale, and results varied without trend in mustard. Relative chlorophyll concentration is correlated with the greenness of a plant, which can also be related to plant quality or leaf N content [25]. This supports the plant tissue results, which reveal no significant differences in N concentrations across treatments in both crops.
Nitrates found in the leachate were lowest in the control for both crops. Since frass contains nitrates, it is reasonable to discern that the higher concentrations of frass produced higher concentrations of nitrate leachate. However, in kale, the BSFL 10% treatment resulted in comparable nitrate concentrations to the control. While results were not significant, a trend of increased leaf tissue concentration for N was observed for both species in the BSFL 10% treatment compared to the control. Thus, it is plausible that the increased nitrates from the incorporation of BSFL frass were utilized by kale, resulting in a similar leachate concentration between BSFL 10% treatment and the control. However, this increased nitrate availability is not reflected in biomass accumulation, as the fresh and dry weights for both kale and mustard were similar between BSFL 10% and the control. This lack of increased yield is likely due to the accumulation of Na in the leaf tissue, as concentrations were higher in both species when BSFL frass was incorporated. Increase in Na uptake was also observed in lettuce and arugula plant tissues grown in BSFL frass [6]. Other studies have reported high Na levels in the frass, often to the detriment of crop growth [23]. Thus, it is likely that the presence of Na in BSFL frass limited potential impacts from increased nitrate availability in the present study.
Other studies [26] discovered increases in ammonium with frass applications. There was little to no ammonium in all our leachate samples (Figure 1f) or frass analysis (Table 2). This could be due to the timing and frequency of testing. We took leachate samples right before final harvest, when much of the ammonium could have already gone through nitrification [27] or leached out of the container. Future studies should also include multiple collections throughout the duration of the experiment. Starting diet for the larvae may also have a large impact on nitrogen in the system. Grasshoppers with diets high in N excreted frass with higher N as well [28]. A study [29] utilized frass from BSFL that were reared on high carbohydrate and protein diets, both of which were supplemented with a concentration of low or high N. These were applied to native soils and compared to an untreated soil control. Soil nitrate and ammonium was highest in the high protein, high N diet. However, this study also observed higher CO2, N2O, and NO fluxes in all frass treatments compared to the control. While increases in N can be valuable for plant uptake of nutrients, it can also pose potential greenhouse gas emissions, so understanding how N moves through the frass incorporated systems will be essential in meeting circular economy principles.
Acidification of soils, which can often be exacerbated by N fertilizer applications, is an increasing concern for growers in certain areas of the world, particularly the Pacific Northwest [30]. This occurs during nitrification by decreasing the pH and therefore increasing the acidity of soil [27]. Soil acidity may also be responsible for decreasing crop productivity. For example, wheat yield stagnates and eventually declines once soil pH drops below 5 [30]. Decreasing N leaching can slow the rate of acidification through methods such as crop rotations and precision nutrient management [31]. A major limitation to this study was our lack of data on pH. Studies with insect frass incorporation have observed small increases in pH over time [32] and this seemed to be mostly impacted by crop type. If the interaction of frass application and crop selection can increase pH, and therefore decrease acidity, future research examining pH of soils and substrates with frass applications could have an important impact on the field.
Based on the results from the present study, BSFL frass at a ratio of 10% could serve as a suitable substitute to peat for greenhouse substrates. While it is possible that higher rates of frass incorporation could reduce the amount of conventional fertilizers required, the presence of excess Na may limit viability. Regardless, increases in soil organic matter and nutrients have been observed in BSFL amended soils [18] which may increase nutrient uptake by the plant [6]. Additionally, the replacement of inorganic fertilizers with a carbon-based source may reduce the risk of surrounding environments to infiltration and leaching [33], similar to what has been seen in other arthropod by products, such as vermicompost [34].

4.2. Study 2 Frass Tea Liquid Applications

Fresh weight was lowest under the FT treatment. This could be due to the lack of sufficient macro- and micronutrients available to support growth, as no supplemental source of fertilization was provided. Based on compost analysis, P and K concentrations were low in the frass utilized to make the tea (Table 2), limiting the availability of these macronutrients throughout production. While FW was lower in the FT treatment, RDW, R:S, and %DW increased compared to MG and FT + MG treatments. Generally, plants will put resources into root growth when substrate nutrient availability is limited [35] (e.g., P and K for the FT treatment). Additionally, since FT was applied directly to the substrate surface, impacts to root growth may have been more prevalent than vegetative growth. Luu et al. (2023) [36] applied vermicompost tea as a foliar spray to Chinese kale grown in three different growing medias and compared these plants to those grown in the three different medias without tea applications. The weight and height of the Chinese kale plants was higher in the tea treatments compared to those without. Thus, the location of FT applications could be an important consideration and warrants further research.
Shoot dry weight is an indicator of increased net primary productivity in leafy plants [37]. While FW was lower in the FT treatment, no difference in SDW was observed between treatments. The resulting increases in %DW in the FT treatment could indicate that BSFL FT applications can alter the water content of vegetative tissues, possibly imposing changes to crop quality or stress resistance (due to less succulent growth).
The partial frass tea treatment (FT + MG) resulted in similar yield and morphology compared to the MG control. These results indicate that FT could be supplemented to reduce or replace conventional fertilizers. Similar results were observed when chicken manure and insect frass were transformed into a nitrate-rich organic liquid fertilizer using a proprietary bioreactor and compared to an inorganic fertilizer control [20]. The fresh weight of basil grown in bioconverted insect frass was comparable to the control. In a study evaluating aquaponics, [38], sweet potato slips and banana peppers provided a liquid frass treatment resulted in increased biomass and productivity. Additionally, similar results have been observed with the utilization of compost teas to reduce fertilizer applications while also providing microbial diversity [39,40]. However, responses to the incorporation of liquid frass appear to be species-, production system-, and product-specific, as both lettuce [41] and sweet potato [42] displayed negative impacts to growth when provided liquid frass as a fertilizer alternative.
A limitation of the present study is lack of a full factorial design. Two positive controls and a treatment were selected to understand the presence/absence of conventional fertility and/or frass tea on kale growth. One treatment comprised of both fertilizer and frass was included to explore how frass tea might impact growth in combination with reduced conventional fertility practices. We selected the specific 100 mL frass tea/100 mL fertilizer treatment to keep the volume consistent across treatments because most growers fertigate based on volume. Future research should explore incorporating a full factorial design of all possible factors (frass tea and conventional fertilizer) and levels (0, 100 and 200 mL) to provide greater context and understanding to possible interactions. Additionally, compost teas have incredibly short shelf lives, so we were unable to test the fermented product for nutritional characteristics. Since the same frass tested and utilized in Study 1 was fermented to make the frass tea in Study 2, we can make assumptions based on those results, but cannot definitively determine how the nutritional composition may have changed.

5. Conclusions

While research on incorporation of insect frass products for horticultural crop production is limited, results generally show moderate additions of frass products result in positive or neutral impacts to yield and other growth parameters. Based on the results from the present study, BSFL frass provides potential benefit as both a substrate and fertilizer alternative. A 10% BSFL frass replacement in a peat-based substrate produced neutral impacts on yield and morphology of both kale and mustard. Similarly, liquid FT applications produced neutral impacts to kale yield and growth when combined with a reduced conventional fertilizer. However, while 10% BSFL frass augmentation in kale did not increase nitrate concentrations in the leachate, the opposite effect occurred in mustard.
Future studies should evaluate the impact of insect frass on pH and cation exchange capacity in tandem with nitrate and ammonium leachate. Further reductions of inorganic fertilizer input in conjunction with solid and liquid frass applications will also be valuable next steps. Creative approaches to frass application methods must be thoroughly examined as this field of inquiry continues to grow.

Author Contributions

Conceptualization, M.Y.C. and A.V.I.; methodology, M.Y.C.; software, M.Y.C. validation, M.Y.C.; formal analysis, M.Y.C.; investigation, M.Y.C. and A.V.I.; resources, J.K.C. and J.B.; data curation, M.Y.C. and A.V.I.; writing—original draft preparation, M.Y.C.; writing—review and editing, A.V.I., J.K.C. and J.B.; visualization, M.Y.C.; supervision, M.Y.C., J.K.C. and J.B.; project administration, J.B. and J.K.C.; funding acquisition, J.B. and J.K.C. All authors have read and agreed to the published version of the manuscript.

Funding

The research materials were funded by Chapul Farms, LLC.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Acknowledgments

CSU Extension Internship; Mike Hazlet and the CSU Horticulture Center; Chapul Farms; CSU Spur; CSU OURA Program; Rebekah Buena, Xenia Rivera Guardado, and Bertha Mendoza for help during data collection.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Agrochemicals 04 00008 g001
Figure 1. Plant Size at harvest (a), Fresh Weight (b), Dry Weight (c), Chlorophyll concentrations (d), Root Weight (e), and Nitrates (f) ± SEM of kale and mustard grown in BSFL frass. Kale and mustard were grown in a 100% peat mix control (CP 100%: white columns) and three treatments with BSFL frass in partial peat mix replacements (BSFL 10% treatment: yellow columns, BSFL 20%: green columns, and BSFL 30%: blue columns). Different letters (Kale a-c and Mustard x-z) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
Figure 1. Plant Size at harvest (a), Fresh Weight (b), Dry Weight (c), Chlorophyll concentrations (d), Root Weight (e), and Nitrates (f) ± SEM of kale and mustard grown in BSFL frass. Kale and mustard were grown in a 100% peat mix control (CP 100%: white columns) and three treatments with BSFL frass in partial peat mix replacements (BSFL 10% treatment: yellow columns, BSFL 20%: green columns, and BSFL 30%: blue columns). Different letters (Kale a-c and Mustard x-z) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
Agrochemicals 04 00008 g001
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Figure 2. Plant Size at Harvest (a), Fresh Weight (b), Dry Weight (c), Percent Dy Weight (d), Chlorophyll concentrations (e), Root Weight (f), and Root to Shoot ratio (g) ±SEM of kale grown with or without BSFL frass tea. Kale was grown in three treatments: BSFL Frass Tea (FT, red columns), Frass Tea and Miracle Gro (FT + MG, violet columns), and Miracle Gro (MG, blue columns). Different letters (a,b) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
Figure 2. Plant Size at Harvest (a), Fresh Weight (b), Dry Weight (c), Percent Dy Weight (d), Chlorophyll concentrations (e), Root Weight (f), and Root to Shoot ratio (g) ±SEM of kale grown with or without BSFL frass tea. Kale was grown in three treatments: BSFL Frass Tea (FT, red columns), Frass Tea and Miracle Gro (FT + MG, violet columns), and Miracle Gro (MG, blue columns). Different letters (a,b) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
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Table 1. Study 1 Experimental Design: Treatment ratios (10, 20, and 30%) of black soldier fly larvae (BSFL) added to a peat-based mix for kale and mustard was compared to a 100% peat control (CP 100%).
Table 1. Study 1 Experimental Design: Treatment ratios (10, 20, and 30%) of black soldier fly larvae (BSFL) added to a peat-based mix for kale and mustard was compared to a 100% peat control (CP 100%).
TreatmentBSFL FrassPeat
CP 100%0% (0 mL)100% (500 mL)
BSFL 10%10% (50 mL)90% (450 mL)
BSFL 20%20% (100 mL)80% (400 mL)
BSFL 30%30% (150 mL)70% (350 mL)
Table 2. Chemical analysis of the BSFL frass that was applied as a partial peat replacement in Study 1 and as fermented liquid product in Study 2. Conventional fertilizer, Miracle Gro, was applied in Study 1 as a standard management practice and in Study 2 as a treatment.
Table 2. Chemical analysis of the BSFL frass that was applied as a partial peat replacement in Study 1 and as fermented liquid product in Study 2. Conventional fertilizer, Miracle Gro, was applied in Study 1 as a standard management practice and in Study 2 as a treatment.
ParameterDry Basis Fertilizer
Dry Matter-Total Solids (%)46.26-
Moisture (%)53.74-
Soluble Salts (mmhos/cm)4.00-
pH8.80-
Organic Nitrogen (%)20.20 -
Ammonium (%)0.05 -
Nitrate (%)0.00 -
Total Nitrogen (%)20.26 24
Phosphorus (%P2O5)1.30 8
Potassium (%K2O)1.7016
Sulfur (%)3.15 -
Calcium (%)4.23 -
Magnesium (%)2.68-
Sodium (%)0.08-
Zinc (ppm)0.0010.12%
Iron (ppm)0.65 0.3%
Manganese (ppm)0.020.1%
Boron (%)-0.02
Copper (%)-0.14
Table 3. Study 2 Experimental Design: Treatments applied weekly for kale grown with a frass tea (FT) treatment application, a Miracle Gro (MG) control, a combined FT + MG treatment.
Table 3. Study 2 Experimental Design: Treatments applied weekly for kale grown with a frass tea (FT) treatment application, a Miracle Gro (MG) control, a combined FT + MG treatment.
TreatmentFrass Tea (mL)Inorganic Fertilizer (mL)
Frass tea (FT)2000
Miracle Gro (MG)0200
FT + MG100100
Table 4. Kale and Mustard Plant Tissue Macronutrient Concentrations ± SE. Kale and mustard were grown in a 100% peat control (CP 100%) and treatments with BSFL frass in partial peat replacements (BSFL 10, 20, and 30%). Different letters (kale: a–b, mustard: x–y) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
Table 4. Kale and Mustard Plant Tissue Macronutrient Concentrations ± SE. Kale and mustard were grown in a 100% peat control (CP 100%) and treatments with BSFL frass in partial peat replacements (BSFL 10, 20, and 30%). Different letters (kale: a–b, mustard: x–y) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
TreatmentN (%)P (%)K (%)S (%)Ca (%)Mg (%)
Kale
CP 100%5.29 ± 0.080.63 ± 0.153.17 ± 0.28 a0.91 ± 0.061.53 ± 0.101.08 ± 0.05
BSFL 10%5.7 ± 0.080.52 ± 0.152.42 ± 0.28 ab0.97 ± 0.061.08 ± 0.100.48 ± 0.05
BSFL 20%6.23 ± 0.080.47 ± 0.150.73 ± 0.28 b1.05 ± 0.061.15 ± 0.100.45 ± 0.05
Mustard
CP 100%5.2 ± 0.040.44 ± 0.04 y2.65 ± 0.09 y1.05 ± 0.051.11 ± 0.09 x0.37 ± 0.06
BSFL 10%5.61 ± 0.040.50 ± 0.04 x5.29 ± 0.09 x0.99 ± 0.050.76 ± 0.09 y0.36 ± 0.06
Table 5. Kale and Mustard Plant Tissue Micronutrient Concentrations ± SE. Kale and mustard were grown in a 100% peat control (CP 100%) and treatments with BSFL frass in partial peat replacements (BSFL 10, 20, and 30%). Different letters (kale: a–b, mustard: x–y) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
Table 5. Kale and Mustard Plant Tissue Micronutrient Concentrations ± SE. Kale and mustard were grown in a 100% peat control (CP 100%) and treatments with BSFL frass in partial peat replacements (BSFL 10, 20, and 30%). Different letters (kale: a–b, mustard: x–y) indicate significant differences between treatments (α = 0.05), ANOVA followed by Tukey’s HSD.
TreatmentNa (%)B (ppm)Cu (ppm)Fe (ppm)Mn (ppm)Zn (ppm)Mo (ppm)
Kale
CP 100%0.36 ± 0.07 b111.50 ± 40.947.55 ± 0.29139.65 ± 16.86 a65.17 ± 4.37118.19 ± 6.83 a0.01 ± 0.003
BSFL 10%1.17 ± 0.07 a58.52 ± 40.948.48 ± 0.2974.45 ± 16.86 b73.15 ± 4.3792.99 ± 6.83 ab0.002 ± 0.003
BSFL 20%1.37 ± 0.07 a98.24 ± 40.948.06 ± 0.2982.17 ± 16.86 ab 66.27 ± 4.37 90.06 ± 6.83 b0.006 ± 0.003
Mustard
CP 100%0.38 ± 0.05 y134.30 ± 50.0915.60 ± 2.64304.10 ± 80.7850.52 ± 5.08147.75 ± 6.150.028 ± 0.01
BSFL 10%1.19 ± 0.05 x65.18 ± 50.0912.94 ± 2.64124.36 ± 80.7852.76 ± 5.08158.88 ± 6.150.008 ± 0.01
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Chavez, M.Y.; Villa Ignacio, A.; Craver, J.K.; Bousselot, J. Investigating Black Soldier Fly Larval (Hermetia illucens) Frass Applications as a Partial Peat Replacement and Liquid Fertilizer in Brassicaceae Crop Production. Agrochemicals 2025, 4, 8. https://doi.org/10.3390/agrochemicals4020008

AMA Style

Chavez MY, Villa Ignacio A, Craver JK, Bousselot J. Investigating Black Soldier Fly Larval (Hermetia illucens) Frass Applications as a Partial Peat Replacement and Liquid Fertilizer in Brassicaceae Crop Production. Agrochemicals. 2025; 4(2):8. https://doi.org/10.3390/agrochemicals4020008

Chicago/Turabian Style

Chavez, Maria Y., Armando Villa Ignacio, Joshua K. Craver, and Jennifer Bousselot. 2025. "Investigating Black Soldier Fly Larval (Hermetia illucens) Frass Applications as a Partial Peat Replacement and Liquid Fertilizer in Brassicaceae Crop Production" Agrochemicals 4, no. 2: 8. https://doi.org/10.3390/agrochemicals4020008

APA Style

Chavez, M. Y., Villa Ignacio, A., Craver, J. K., & Bousselot, J. (2025). Investigating Black Soldier Fly Larval (Hermetia illucens) Frass Applications as a Partial Peat Replacement and Liquid Fertilizer in Brassicaceae Crop Production. Agrochemicals, 4(2), 8. https://doi.org/10.3390/agrochemicals4020008

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