The research team, led by Sylvie Skalickova and Pavel Horky, set out to test whether two commercially available and fast-growing bacteria could unlock the nutritional potential locked inside milling waste. They chose Lactiplantibacillus plantarum, a homofermentative lactic acid bacterium equipped with enzymes capable of degrading cellulose-rich polysaccharides, and Bacillus subtilis, a sporulating species whose enzymatic repertoire includes proteases, amylases and lipases. Both organisms can also produce secondary metabolites such as organic acids, phenolic compounds and flavonoids, which could enrich the fermented material beyond simple nutrient release. Prior work on fermentation-based biofertilizers had focused mostly on rice bran, fruit pomace, olive waste and other substrates rich in readily digestible nutrients, leaving heterogeneous grain milling waste largely unexplored.

In the first stage of the experiment, the researchers optimized the fermentation process in vitro. Substrates of wheat bran, feed-grade wheat flour and mill dust were mixed in three ratios, submerged in water, pre-treated with xylanase at 45 degrees Celsius for 24 hours, and then inoculated with either bacterial species at two different doses. Cultivation proceeded aerobically at 37 degrees Celsius under mild agitation for 48 hours. The team then measured markers of microbial activity, including glucose, lactic acid, total polyphenols and total protein, alongside the bioavailability of phosphorus and micronutrients in both the liquid supernatant and the solid pellet.

The results were striking. Fermented milling waste showed a two-fold increase in total protein concentration and a 6.5-fold increase in lactic acid concentration compared with the unfermented control. Free phosphorus availability doubled, and soluble mineral ions rose significantly across the board: calcium increased by 3 to 9 milligrams per liter, iron by 4.5 to 9.9 milligrams per liter, magnesium by 7.5 to 13 milligrams per liter, manganese by 13 to 15 milligrams per liter and zinc by 8.5 to 9.3 milligrams per liter. Importantly, these effects were not strictly dose-dependent, and the outcome depended on both the bacterial strain and the substrate composition. Most microelements accumulated in the liquid fraction, while calcium concentrated in the pellet, a pattern the authors attribute in part to microbial acidification of the medium, which promotes the release of mineral ions from polysaccharide complexes.

The substrate ratios mattered too. Bacillus subtilis fermentation of the bran-heavy 6:3:1 mixture produced a sharp rise in lactic acid alongside a steep drop in free glucose, whereas L. plantarum continued to consume glucose without being inhibited by rising acidity. The authors note that the elevated acid readings in the Bacillus treatments may reflect other organic acids interfering with the lactic acid assay rather than lactic acid itself. Fermentation also significantly increased total polyphenol content in all treatments, consistent with microbial hydrolysis of cell-wall components releasing bound phenolic compounds. Based on the combined in vitro data, the team selected L. plantarum and the 6:2:2 substrate ratio for the next stage, because this combination maximized the inclusion of hard-to-use mill dust while delivering strong mineral solubilization and high lactic acid production, which can also help protect plants against pathogens.

With the fermented material, or FMW, in hand, the researchers moved to a greenhouse pot experiment with maize (Zea mays). FMW was applied in three ways: incorporated directly into the soil, sprayed onto leaves as a foliar treatment, or poured onto the soil as a drench. Each route was benchmarked against mineral NPK fertilizer, compost, vermicompost and an unfertilized control, with fertilizer doses converted from an intensive field rate of 250 kilograms of nitrogen per hectare. Over three 14-day sampling intervals, the team tracked aboveground biomass, leaf chlorophyll as a proxy for nitrogen status, soil mineral nitrogen, soil pH and the concentrations of macro- and micronutrients in both soil and plant tissue.

The growth results revealed a clear hierarchy. NPK fertilizer produced the highest and statistically most significant biomass at every sampling date, as expected from its instantly soluble nutrients. Direct soil incorporation of FMW, by contrast, yielded the lowest biomass, between 9 and 25 percent below the unfertilized control, likely because the carbon-rich substrate stimulated rapid microbial proliferation that temporarily immobilized nitrogen needed by young plants. Yet the liquid application routes told a different story. Foliar FMW produced the relatively highest dry weight gains in the first two sampling terms, at 12 and 9 percent above control, while soil drenching with FMW delivered a 21 percent biomass advantage by the final harvest. The authors suggest that foliar and drench applications bypass soil microbial competition altogether, delivering amino acids and bioactive compounds directly through the leaf cuticle or the root zone.

The soil chemistry data added further nuance. Among the organic treatments, FMW consistently provided the highest soil mineral nitrogen, reaching 22.2 milligrams per kilogram in the final sampling compared with 12.95 for the control, 13.37 for compost and 13.23 for vermicompost. FMW also produced the highest ammonium nitrogen fractions among the organic treatments in every term, a form of nitrogen that persists longer in soil and serves as a reserve against leaching. Correlations between soil mineral nitrogen and leaf chlorophyll were strong to very strong, with Pearson coefficients ranging from 0.79 to 0.94. Soil drenching with FMW also produced the highest soil pH values at every sampling, a buffering effect the authors link to basic cations such as calcium and magnesium displacing exchangeable hydrogen and aluminum ions, in welcome contrast to the acidifying tendency of mineral fertilizers.

Plant tissue analysis underscored the biostimulant potential of the fermented waste. FMW applied to soil or as a drench produced the second-highest concentrations of phosphorus, calcium, iron and copper after NPK, and delivered statistically the highest tissue levels of magnesium and zinc of any treatment. Relative to the unfertilized control, FMW soil application or drenching raised plant content of phosphorus by 23 percent, potassium by 50 percent, calcium by 31 percent, sulfur by 36 percent, iron by 40 percent and manganese by a remarkable 86 percent. The authors attribute this micronutrient mobilization to chelation by organic acids and humified compounds released during fermentation, which keep metals soluble and plant-available even in near-neutral soils.

The study’s conclusion is deliberately measured: fermented milling waste is not a replacement for mineral fertilizer, which remains unmatched for short-term yield, but rather a complementary organic amendment with a genuine biostimulant dimension whose value depends heavily on how it is applied. Compared with compost and vermicompost, which take weeks to months to produce, controlled fermentation offers a far faster route from waste to usable product, fitting neatly into circular bioeconomy goals. The authors caution that pot experiments cannot be directly extrapolated to the field, and that environmental and safety questions, including salt accumulation, phytotoxic compounds, pathogen contamination and heavy-metal loading, remain to be assessed. Multi-year field trials will be needed to quantify cumulative effects on soil organic carbon, microbial activity and yield stability. Still, the prospect of turning one of agriculture’s most stubborn waste streams into a liquid amendment that feeds soils, nourishes crops and buffers acidity marks a compelling step toward more sustainable cereal processing.

Subject of Research: Microbial fermentation of grain milling waste as an organic soil amendment and biostimulant for crop nutrition

Article Title: Utilization of grain milling waste for plant growth and nutrient availability in soil

Article References: Skalickova, S., Antosovsky, J., Ridoskova, A., Ryant, P., & Horky, P. (2026). Utilization of grain milling waste for plant growth and nutrient availability in soil. Frontiers in Sustainability, 7, Article 1958097. https://doi.org/10.3389/frsus.2026.1958097

Image Credits: AI Generated

DOI: 10.3389/frsus.2026.1958097

Keywords: grain milling waste, fermentation, Lactiplantibacillus plantarum, Bacillus subtilis, biofertilizer, soil health, plant nutrition, biostimulant, circular economy, wheat bran, organic amendment, maize