The study, published in the journal Discover Soil, set out to answer a deceptively simple question: does the way a chicken is raised change the pollution profile of its manure? The answer, according to the team led by Oladele Abdulahi Oguntade, is a clear yes. Commercial chicken manure, or CCM, collected from more than three thousand ISA Brown laying hens fed on maize and groundnut cake concentrates, contained more than four times the manganese and copper found in free-range manure. Zinc and cadmium were also elevated in the commercial product. Only iron and nickel ran counter to the trend, with free-range manure containing more than seven times the iron, likely because the birds pecked at small stones and pebbles in the surrounding soil.

The origin of these toxic elements lies in the poultry diet itself. Concentrate feeds, mineral supplements and veterinary drugs given to caged birds contain additives rich in copper, cadmium and manganese, and because chickens do not fully digest these elements, the residues pass straight into their droppings. When that manure is spread on fields as fertilizer, the metals ride along. Elements with densities above five grams per cubic centimeter and long biological half-lives, such as cadmium, are particularly concerning because they persist in soil and can enter the food chain, with documented damaging effects on the brain, lungs, liver and kidneys.

To quantify the risk, the researchers ran a carefully controlled pot experiment. Thirty buckets, each holding five kilograms of acidic loamy sand collected from the university’s Teaching and Research Farm at Ayetoro, were amended with either commercial or free-range manure at four rates: 4, 6, 8 and 10 tonnes per hectare, equivalent to 11.39 to 28.46 grams of dry manure per pot. An unamended control completed the design, and each treatment was replicated three times in a completely randomized layout. After two weeks of equilibration, cockscomb seeds were sown, seedlings were thinned to one per pot, and the plants were grown for six weeks under screen-house conditions before harvest.

Chemical analysis told a consistent story. Concentrations of copper, manganese and zinc in the soil rose with manure rate and were significantly higher in plots treated with commercial manure than with free-range product. At the lowest application rate of four tonnes per hectare, cadmium in the soil jumped by 103.8 percent with commercial manure and 66.8 percent with free-range manure compared to unfertilized soil. The team then applied a battery of pollution indices, including the contamination factor, degree of contamination, elemental pollution index and pollution load index, all standard tools for grading soil contamination. By these measures, commercial manure pushed the soil into severe and even extreme contamination categories at the highest rate, with a pollution load index at or above five, while manganese remained the least problematic element with contamination factors below one.

Interestingly, the amendments did not simply dump metals into an inert system. The manure raised soil pH, organic carbon and effective cation exchange capacity, the latter by 92.7 percent, and these changes altered how the metals behaved. Higher pH and abundant organic matter encouraged cadmium, copper and manganese cations to bind at cation exchange surfaces and onto organic ligands, reducing their dissolution and immediate bioavailability. The researchers found that the pollution load index itself modified soil pH by about 2.29 units, a feedback that helped restrain the transfer of metals from root to shoot. In other words, the same organic matter that fertilizes the crop also acts as a partial chemical buffer, at least in the short term.

But buffering has limits, and the cockscomb plants revealed them. The team calculated three phytoextraction metrics for each metal: the bioconcentration factor, comparing root concentration to soil concentration; the bioaccumulation coefficient, comparing edible shoot to soil; and the translocation factor, comparing shoot to root. Copper and manganese accumulated significantly more in both roots and shoots of plants grown with commercial manure than with free-range manure. Copper proved the more mobile traveler, with phytoextraction exceeding that of manganese, and its bioaccumulation coefficient climbed steadily at rates of six tonnes per hectare and above, a pattern the authors attribute to soluble metal-organic complexes forming in the soil solution at high manure doses.

The translocation story added a twist. Free-range manure actually promoted greater copper movement from root to shoot than commercial manure, despite containing less copper overall, while commercial manure favored manganese mobility. This shows that the journey of a toxic element through a plant depends not just on how much is present in the soil but on the chemistry of the amendment itself, particularly the dissolved organic carbon it releases and the pH shifts it induces. Manganese translocation, by contrast, dropped with rising manure rates, suggesting that at high doses the amendments effectively immobilized manganese in the root zone, with uptake peaking at eight tonnes per hectare and declining thereafter.

For farmers and consumers, the practical message is a dose threshold. Growth and yield of the cockscomb responded strongly to manure, with the best performance at eight tonnes per hectare for commercial manure and ten for free-range, yet the yields achieved at four tonnes per hectare were statistically comparable. Since the edible shoots carried potentially risky levels of copper and manganese above six tonnes per hectare, the authors argue that lower application rates deliver nearly the same agronomic benefit with far less contamination. Applying chicken manure above that threshold, especially the commercial variety, should be avoided to keep metals out of the food chain.

The study has clear boundaries. It was a pot experiment under controlled conditions, and the authors themselves call for field trials that track metals through topsoil and subsoil layers, for broader pollution indicators, and for health risk assessments of people who actually consume the crop in the region. Still, the findings land at an uncomfortable moment for organic agriculture, which leans heavily on animal manures worldwide. They suggest that organic is not automatically clean, that the industrial feed and drug regime behind battery-cage eggs leaves a metallic fingerprint in the fertilizer it produces, and that even a humble leafy green like cockscomb can become an unwitting courier of that fingerprint to the dinner plate. Sustainable farming, the study implies, needs to count not only nutrients but contaminants, gram by gram, in every scoop of manure it spreads.

Subject of Research: Accumulation of potentially toxic elements from chicken manure amendments in soil and cockscomb vegetables

Article Title: Accumulation of potentially toxic elements in cockscomb (Celosia argentea Linn) grown in soil amended with chicken manure

Article References: Oguntade, O. A., Yisa, N. M., Olagunju, S. O., Odelana, T. B., Adewusi, K. M., Odusanya, O. A., & Abifarin-Adegbenro, R. O. (2026). Accumulation of potentially toxic elements in cockscomb (Celosia argentea Linn) grown in soil amended with chicken manure. Discover Soil, 3(1), Article 154. https://doi.org/10.1007/s44378-026-00311-z

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00311-z

Keywords: chicken manure, potentially toxic elements, cockscomb, soil contamination, heavy metals, organic farming, pollution load index, bioaccumulation, copper, cadmium, manganese, soil amendment

The research team, led by Wojciech Jerzak of AGH University of Krakow, pyrolyzed both materials at 700, 800 and 900 degrees Celsius in a fixed-bed reactor flushed with high-purity nitrogen. Each 1.5-gram sample was held at the target temperature for one hour, after which the resulting chars were ground, sieved and subjected to a battery of analytical techniques including Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nitrogen sorption analysis. Carbon dioxide uptake was then measured at 20 degrees Celsius across pressures ranging from 0.5 to 110 kilopascals.

The starting materials could hardly have been more different. Chicken manure, collected from a poultry farm in southern Poland, contained just 8 percent fixed carbon but a hefty 26.4 percent ash, along with 4.1 percent nitrogen. Onion peels from a processing facility in the Kuyavian-Pomeranian Voivodeship were richer in combustible material, with 56.4 percent volatile matter, 14.9 percent fixed carbon and a lignocellulosic structure containing substantial cellulose and hemicellulose. X-ray fluorescence showed that calcium oxide dominated the ash of both feedstocks, at 48.8 percent for the manure and 40.8 percent for the peels, but the manure also carried elevated potassium, phosphorus, magnesium and sulphur, while the peels were unusually rich in silica at 33.8 percent.

As pyrolysis temperature climbed, both feedstocks lost mass, moisture and volatile components while their ash fractions concentrated in the solid residue. Manure biochar ash content soared from 26.4 percent in the raw material to 65.2 percent at 900 degrees Celsius, while onion peel biochar ash rose from 14.9 to roughly 41.8 percent. Hydrogen contents in both biochars fell below 1 percent, and nitrogen in the manure chars dropped from 4.1 to between 1.1 and 1.8 percent, reflecting the thermal cracking of volatile compounds and the release of small nitrogenous molecules. Onion peel biochars, by contrast, concentrated carbon to around 50 to 52 percent, more than the manure chars managed, thanks to their lower initial mineral burden.

Spectroscopy traced the chemical evolution in fine detail. Infrared spectra showed the progressive disappearance of hydroxyl, aliphatic and carbonyl bands with rising temperature, signalling dehydration, decarboxylation and the growth of a condensed aromatic carbon matrix. Yet phosphate and carbonate signals persisted in the manure-derived chars, underscoring the thermal stability of their inorganic constituents. X-ray diffraction revealed dramatic mineral reorganisation: at 700 degrees Celsius the manure char held quartz, portlandite and rutile, but by 800 and 900 degrees Celsius the ash had transformed into calcium oxide, whitlockite-type calcium-magnesium phosphates, magnesite, oldhamite and eventually sulfoapatite. The onion peel chars followed a different path, developing graphitic carbon alongside quartz, kalsilite, sodium carbonate and, at the highest temperature, the stable alkali aluminosilicate sanidine.

Electron microscopy captured the morphological consequences. Manure biochars remained dense, heterogeneous aggregates with no well-defined pore network, their high mineral content apparently filling or masking the developing carbon porosity. The onion peel chars told a more elegant story: at 700 degrees Celsius they retained elongated, layered fragments of the original plant tissue, and at 800 degrees Celsius they developed a striking channel-like structure the authors liken to a fish skeleton, with aligned, interconnected spaces carved out by devolatilisation. At 900 degrees Celsius, however, that ordered architecture began to fragment and partially collapse, a warning that excessive heat can destroy the very structure adsorbent designers hope to build.

Porosity measurements quantified these visual impressions. The onion peel biochar produced at 900 degrees Celsius achieved the highest specific surface area of the entire study, 109.8 square metres per gram—more than three times that of its 800-degree counterpart and nearly 6.5 times that of the 700-degree sample—with micropores contributing up to 60 percent of the internal surface in the intermediate-temperature samples. Manure biochars reached more modest areas between 14.0 and 36.2 square metres per gram, but their average pore diameter also shrank steadily with temperature, indicating progressive micropore refinement.

The carbon dioxide adsorption results upended the expectation that bigger surface area always means better capture. Among the onion peel chars, the 700-degree sample—despite its modest 17 square metres per gram—delivered the highest uptake, 26.6 cubic centimetres per gram at 100 kilopascals, while the 900-degree sample with the largest surface area actually adsorbed less. The researchers attribute this to pore widening and a shrinking population of narrow ultramicropores, those cavities below 0.7 nanometres whose dimensions closely match the kinetic diameter of CO2 and which nitrogen adsorption at cryogenic temperatures cannot fully resolve. Residual oxygen-containing surface groups may also enhance CO2-surface interactions in the cooler char.

The manure biochars behaved in almost mirror-image fashion, with CO2 uptake rising steadily as pyrolysis temperature increased, tracking the growth of microporosity and surface area. But texture alone could not explain the performance of the 900-degree manure char, which captured substantial CO2 despite a smaller surface area than its onion peel rivals. X-ray diffraction and fluorescence pointed to the missing piece: calcium oxide and calcium-rich phosphate phases that furnish basic adsorption sites with a strong affinity for acidic CO2 molecules, potentially even fixing some of the gas chemically as carbonate or bicarbonate species. In these mineral-rich chars, capture is a partnership between physical pore-filling and mineral-assisted interaction.

The practical lesson is that biochar design must be matched to feedstock chemistry. For lignocellulosic wastes like onion peels, the goal should be preserving narrow micropores rather than maximising total surface area, and avoiding the pore widening and structural collapse that come with excessive heat. For manures, engineers should exploit the inherent calcium, magnesium and potassium phases that add a chemical dimension to capture. Converting two problematic wastes into tailored carbon sorbents in a single thermal step offers a double dividend—waste valorisation and carbon management—grounded not in exotic chemistry but in a careful reading of what heat does to the organic and mineral halves of agricultural residue.

Subject of Research: Thermal conversion of chicken manure and onion peels into biochars for carbon dioxide adsorption

Article Title: Effect of thermal treatment on the structure and CO2 adsorption capacity of biochar from chicken manure and onion peels

Article References: Effect of thermal treatment on the structure and CO2 adsorption capacity of biochar from chicken manure and onion peels. (n.d.). https://doi.org/10.1007/s10098-026-03598-2

Image Credits: AI Generated

DOI: 10.1007/s10098-026-03598-2

Keywords: biochar, pyrolysis, CO2 capture, chicken manure, onion peels, carbon adsorption, microporosity, mineral phases, waste valorisation, X-ray diffraction, Raman spectroscopy, surface area