The research, led by Andrii Dankevych of the National University of Food Technology in Kyiv together with colleagues from Ukraine, Lithuania and Uganda, set out to test whether sunflower husk ash, or SHA, could serve as a genuine secondary mineral resource within a circular economy. The logic is elegantly simple. Sunflower plants draw potassium, phosphorus, calcium, magnesium and sulfur out of the soil as they grow. When the husks are burned for energy, those minerals are not destroyed; they are concentrated in the ash. Returning that ash to farmland effectively closes a nutrient loop that industrial agriculture has traditionally left wide open, sending minerals off-site and replacing them with mined, energy-intensive synthetic fertilizers.

The chemistry of the ash-based fertilizer is central to the story. According to the study, the SHA fertilizer contained 30 percent potassium oxide, 5 percent phosphorus pentoxide, 9 percent calcium oxide, 10 percent magnesium oxide and 4 percent sulfur. Notably, it contained no chlorine at all. That composition matters for two reasons. First, the high potassium fraction makes it a credible alternative or supplement to conventional potash fertilizers, which are among the most geopolitically sensitive and price-volatile inputs in modern farming. Second, the absence of chloride is an advantage for crops such as potato, tomato and cucumber, which are known to be sensitive to chloride accumulation in soil.

To test the fertilizer under real field conditions rather than in pots or greenhouses, the team conducted experiments during one growing season at the Slobozhanske Experimental Field of the National Scientific Center O.N. Sokolovsky Institute for Soil Science and Agrochemistry Research in Ukraine. The soil was a typical heavy loam chernozem, the famously fertile black earth that underpins much of Eastern Europe’s agricultural output. Seven crops were evaluated side by side: barley, maize, sunflower, potato, tomato, table beet and cucumber. Each crop occupied a plot of 0.1 hectares, allowing the researchers to observe how the ash-based fertilizer performed across a genuinely diverse rotation of cereals, oilseeds, tubers and vegetables.

The experimental design compared four treatments for each crop: an unfertilized control, a conventional NPK 16:16:16 mineral fertilizer, and the SHA-based fertilizer applied at two rates, 200 and 300 kilograms per hectare. The ash fertilizer was delivered in two ways, as a basal application and during pre-sowing cultivation, so the researchers could see whether timing and placement influenced performance. Yield, soil agrochemical properties and selected quality parameters of the harvested products were then measured, and the data were processed using descriptive and comparative statistical methods, including arithmetic means and absolute and relative differences between treatments.

The headline result is that plots treated with the SHA-based fertilizer yielded approximately 10 to 18 percent more than the unfertilized controls. Just as important for long-term soil health, the content of mobile phosphorus and exchangeable potassium in the soil rose by roughly 10 to 22 percent following treatment. Soil pH shifted by approximately 0.3 to 0.5 units, a change consistent with the liming-like effect of the calcium and magnesium oxides in the ash, which can help buffer acidity in intensively farmed soils. Beyond quantity, the researchers also recorded improvements in quality parameters of the produce itself, including higher dry matter, protein and fat content in the harvested crops, suggesting that the ash-derived nutrients were genuinely feeding the plants rather than merely sitting in the soil.

The authors are careful, and rightly so, about the limits of what a single-season, single-site trial can prove. Because all the data came from one growing season at one experimental station, the results reflect the specific soil, climatic and experimental conditions of the study and should be interpreted descriptively rather than as statistically significant effects. That caveat is standard scientific caution, but it is also a roadmap: the team explicitly calls for further studies in different natural and climatic zones and on soils with different properties to establish whether the yield gains and soil improvements hold up more broadly. Multi-year trials would also be needed to confirm that repeated ash application does not lead to unwanted accumulations of trace elements, a question that remains open for many waste-derived fertilizers.

Even with those caveats, the scale of the opportunity is hard to ignore. Ukraine is one of the world’s largest sunflower producers, and the husk that remains after oil extraction is widely burned in boilers as biomass fuel. That combustion, while renewable in energy terms, produces ash streams exceeding 100 thousand tonnes per year that currently must be landfilled or otherwise disposed of, at cost to processors and with no agronomic return. If even a fraction of that ash were diverted into fertilizer production, it would simultaneously reduce waste disposal volumes, displace demand for imported or mined potassium and phosphorus, and return nutrients to the very fields that grew the crop. This is the circular economy in its most literal form: minerals harvested from the soil, used in processing, burned for energy, and then sent home again.

The study also carries broader implications for the bioeconomy beyond Ukraine. Sunflower is grown commercially across Europe, the Black Sea region, Argentina and elsewhere, and husk ash is a ubiquitous by-product of the oilseed industry wherever husks are used as fuel. The Ukrainian findings provide initial field evidence that this ash stream, rather than being a niche curiosity, can function as a standardized fertilizer input with a defined nutrient profile. Because the ash is essentially a concentrated, chlorine-free potassium source with secondary phosphorus, calcium, magnesium and sulfur, it could be blended or granulated with other materials to create tailored formulations for chloride-sensitive crops, organic-adjacent production systems, or regions where conventional potash supplies are expensive or unreliable.

What makes the work resonate beyond agronomy is its framing of waste as a design flaw rather than an inevitability. The researchers argue that valorizing sunflower processing residues can contribute to added value, increased agricultural production and the implementation of environmental initiatives all at once, turning a disposal liability into a revenue stream and a soil amendment in a single move. As fertilizer prices remain volatile and the environmental footprint of synthetic nutrient production draws increasing scrutiny, studies like this one point toward a pragmatic middle path: not a rejection of mineral fertilizers, but a smarter, more circular sourcing of them. The next seasons of field trials will determine whether sunflower husk ash can graduate from promising one-site evidence to a dependable ingredient of sustainable agriculture. For now, the message from the chernozem of eastern Ukraine is clear: the minerals that leave the farm in a sunflower seed do not have to be gone for good.

Subject of Research: Use of sunflower husk ash as a secondary mineral resource for fertilizer production in circular-economy agriculture

Article Title: Agricultural waste valorization in the circular economy using sunflower husk ash as a secondary resource

Article References: Dankevych, A., Nitsenko, V., Dankevych, V., Ogbu, E. F., Lastauskaitė, A., & Kapelista, I. (2026). Agricultural waste valorization in the circular economy using sunflower husk ash as a secondary resource. Discover Sustainability. https://doi.org/10.1007/s43621-026-04879-y

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04879-y

Keywords: sunflower husk ash, circular economy, agricultural waste valorization, fertilizer, crop yield, soil nutrients, chernozem, potassium, biomass energy, sustainable agriculture, Ukraine, bioeconomy

The research team, led by Kseniia Bondar of the Institute of Geophysics at the Polish Academy of Sciences, collected PBR as a magnetic extract from surface deposits at Stari Petrivtsi, a demolition site in the Kyiv region where controlled detonations of various munitions have been carried out since 2013. The magnetic fraction made up roughly one percent of the surface material by weight, so the researchers mixed the same proportion into natural Chernik Phaeozem soil sampled from an unploughed site in the Kharkiv region, replicating the contamination levels expected on frontline agricultural land subjected to prolonged shelling.

Under the scanning electron microscope, the residue revealed a two-part architecture. Angular metal fragments and spherical particles ranging from one to one hundred micrometres across were both built around a core of nearly pure metallic iron, sheathed in a corroded outer layer of iron oxides. Energy-dispersive X-ray analysis showed that the spherules carried a cocktail of potentially toxic elements, including copper, tin, lead, chromium, manganese and zinc, while the fragments additionally contained tungsten, molybdenum, aluminium, vanadium and antimony. Some spherules were dominated instead by antimony and lead, a reminder that munition alloys leave a varied chemical fingerprint in the ground.

To test how this debris behaves in a living soil, the team sealed the contaminated and control soils in containers with water, reproducing the waterlogged conditions that follow spring snowmelt or heavy summer rain on the heavy clay-rich chernozems of the region. For twenty days they tracked pH, redox potential, bacterial growth, dissolved organic carbon and the composition of gases in the sealed headspace, alongside colorimetric measurements of soluble ferrous and ferric iron. In the plain soil and the soil-plus-residue treatments, microbial metabolism stayed modest: oxygen drifted down from twenty-one to a few percent, pH eased from 7.8 to 7.0, and soluble iron never climbed above roughly fifty to eighty-five milligrams per litre.

The picture changed dramatically when the researchers added potato as a carbon and energy source, simulating the organic inputs that roots and crop residues provide in a real field. Fermenting microbes rapidly consumed the remaining oxygen, drove the redox potential from plus 420 down to minus 205 millivolts, and dropped the pH to 4.2. Hydrogen and carbon dioxide surged to fifty-eight and seventy-two percent of the gas phase respectively, while dissolved organic carbon jumped from 140 to 1200 milligrams per litre. Against this backdrop of intense anaerobic fermentation, soluble Fe(II) peaked at 960 milligrams per litre and Fe(III) at 420 milligrams per litre on day twelve, an order of magnitude above the low-activity treatments.

The mechanism the authors propose is a two-step partnership between biology and chemistry. Microorganisms cannot oxidise metallic iron directly, because the redox potential of the Fe(0) oxidation reaction sits below that of even hydrogen fermentation. Instead, iron metal is attacked abiotically by protons derived from water. What the microbes do is strip away the protective rust. Fermentation generates organic acids and protons that chelate and dissolve the iron oxide and hydroxide coatings on the fragments, exposing fresh metal and accelerating the chemical conversion of Fe(0) to soluble Fe(II). Vigorous gas release also stirs away reaction products from particle surfaces. In effect, the soil microbiome acts as a biocatalyst for the corrosion of its own contamination.

Magnetic measurements told a parallel story. Adding one percent PBR raised the soil’s mass-specific magnetic susceptibility by roughly thirty to fifty percent, and thermomagnetic analysis confirmed the presence of both magnetite and metallic iron in the residue. Yet waterlogging selectively dissolved the fine-grained, superparamagnetic magnetite produced naturally in the soil, halving the anhysteretic remanence in both control and contaminated samples. Unmixing of isothermal remanence acquisition curves showed that the highly coercive rust coating on the fragments, with coercivities near one hundred to one hundred sixty millitesla, decayed under waterlogged conditions, while the intermediate-coercivity signature of the spherules, between forty-seven and fifty-five millitesla, remained essentially untouched. After microbial stimulation, the coarse multidomain magnetite of the spherules came to dominate the entire magnetic spectrum, echoing the remarkable persistence of industrial fly-ash particles in peat bogs and lake sediments.

The biological consequences were assessed with seed germination and seedling growth assays using wheat and three Brassicaceae species: white mustard, radish and garden cress. Germination proved remarkably insensitive, staying above ninety-five percent in wheat, radish and cress regardless of contamination. Early seedling growth was a different matter. In radish, root elongation fell by eighteen percent and shoot growth by about twenty-one percent; in garden cress, roots shortened by twenty-two percent and shoots by nineteen percent, differences confirmed as statistically significant by Mann-Whitney tests. Wheat, by contrast, showed no measurable inhibition, and water extracts of the contaminated soil were nearly harmless, pointing to processes at the soil-root interface rather than bulk solution chemistry as the driver of toxicity.

Iron accumulation data reinforced the species-specific nature of the response. Wheat roots sequestered enormous quantities of iron, up to 6401 milligrams per kilogram in contaminated soil, while keeping shoot concentrations low, a classic excluder strategy that immobilises excess metal in the root apoplast and vacuoles. White mustard, in contrast, loaded its shoots with more than 1000 milligrams per kilogram of iron, whereas radish and cress actually transported less iron to their shoots under contamination, apparently throttling translocation through regulatory systems such as the IRT1 transporter and FRO2 reductase. Notably, the degree of growth inhibition did not track tissue iron levels, indicating that rhizosphere availability of Fe(II) during a transient window of mobilisation, roughly days eight to twenty-one of incubation, matters more than the iron ultimately stored in the plant.

The authors caution that their findings come from closed laboratory systems and must be validated in the field, where open mass exchange and repeated wetting cycles could amplify or dilute these effects. Even so, the study offers the clearest picture yet of how war debris ages in fertile farmland: rusted fragments slowly dissolve under microbial pressure, releasing pulses of bioavailable iron that stress sensitive seedlings, while the explosion-derived spherules persist as a durable magnetic fingerprint. For the vast agricultural regions of Ukraine awaiting demining and recovery, the message is that the environmental legacy of shelling is not static. It is a living geochemical process, driven by the smallest inhabitants of the soil, and its full consequences for crop safety and food-chain transfer are only beginning to come into focus.

Subject of Research: Microbial and magnetic transformation of post-blast weapons residue and its phytotoxic effects in Ukrainian chernozem soils

Article Title: Fate of post-blast residue in soils from an armed conflict zone determined by magnetic, microbiological, and ecotoxicological assessments

Article References: Fate of post-blast residue in soils from an armed conflict zone determined by magnetic, microbiological, and ecotoxicological assessments. (n.d.). https://doi.org/10.1007/s10653-026-03497-x

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03497-x

Keywords: post-blast residue, soil contamination, armed conflict, iron mobilization, soil microbiome, magnetic susceptibility, phytotoxicity, chernozem, waterlogging, seedling growth, Ukraine, biogeochemistry