Brazil cultivates coffee across approximately 2.25 million hectares, and the crop’s famously high productivity rests on heavy applications of mineral fertilizers, particularly nitrogen. Nitrogen is the engine of plant metabolism, forming the structural backbone of proteins, nucleic acids, and chlorophyll, and coffee plants grown in full-sun monocultures demand enormous quantities of it during vegetative growth, flowering, and fruit filling. But synthetic nitrogen inputs are notoriously inefficient: a large fraction is lost to leaching, volatilization, and denitrification before the plant can use it, driving up production costs while polluting waterways and warming the atmosphere. That inefficiency has pushed scientists to look beneath their feet for alternatives.

The research team focused on two adjacent coffee-producing areas in the municipality of Araponga, in the state of Minas Gerais, both planted with the Catuaí Vermelho variety at roughly 900 meters altitude and both cultivated for more than fifteen years. One farm followed conventional mineral fertilization, receiving 1,250 kilograms per hectare of NPK fertilizer split into two doses, along with lime. The other practiced organic fertilization, applying 400 kilograms per hectare of urea together with 6,000 kilograms per hectare of composted chicken litter. Soil samples were collected in November 2023 during the flowering stage, with ten composite samples gathered per farm from bulk soil around the tree trunks.

To coax out bacteria capable of living without fixed nitrogen, the team plated soil dilutions onto two nitrogen-free culture media, LGI and JMV, traditionally used to enrich diazotrophic bacteria. In total, thirty-eight morphologically distinct bacterial isolates were purified—nineteen from each farm—and identified by Sanger sequencing of the 16S rRNA gene, the standard molecular barcode for bacteria. The isolates spanned four phyla and fifteen genera, with members of Pseudomonadota and Actinomycetota dominating both farms. Intriguingly, isolates from the phyla Bacillota and Bacteroidota emerged exclusively from the organically fertilized soil, hinting that compost inputs had opened ecological niches that mineral fertilizer alone could not.

Only three genera—Pseudomonas, Streptomyces, and Acinetobacter—were shared between the two management systems. The organic farm exclusively yielded Paraburkholderia, Priestia, Flavobacterium, Curtobacterium, and Dyella, while the conventional farm alone harbored Burkholderia, Ralstonia, Luteibacter, Kosakonia, and Rhizobium. The researchers attribute these management-specific profiles to differences in carbon inputs and nutrient dynamics, noting that organic amendments generally increase soil organic carbon and niche heterogeneity, whereas mineral fertilization favors fast-growing copiotrophic microbes that exploit sudden nutrient pulses. The recovery of Rhizobium and Luteibacter under conventional fertilization was particularly noteworthy, expanding knowledge of these genera’s distribution in coffee agroecosystems.

The functional screening was where the study’s biotechnological promise crystallized. Eleven isolates from the organic farm and nine from the conventional farm grew in nitrogen-free semi-solid NFb medium, forming the subsurface microaerophilic pellicles and alkalinizing the indicator dye that signal a putative diazotrophic phenotype—the ability to convert atmospheric nitrogen into biologically usable forms. Even more striking, every single isolate recovered from the organically fertilized soil could solubilize tricalcium phosphate in vitro, dissolving an otherwise inaccessible mineral pool of phosphorus into forms plants can absorb. Standout performers included Streptomyces, Bacillus, Flavobacterium, and Acinetobacter strains with solubilization indices above 3, the threshold for classification as high-efficiency solubilizers.

Phytohormone production added a third dimension to the isolates’ toolkit. Quantified spectrophotometrically after growth in tryptophan-supplemented medium, indole-3-acetic acid—the principal auxin that stimulates root development—was produced by isolates from both farms, with no statistically significant difference between the two management systems. The most prolific producers included Priestia, Dyella, Paraburkholderia, and Bacillus from the organic soil, and Streptomyces and Luteibacter from the conventional soil. One Streptomyces isolate reached concentrations of up to 68.82 micrograms per milliliter, exceeding values previously reported for well-characterized plant growth-promoting Streptomyces strains, a result the authors describe as reinforcing the biotechnological potential of these genera.

What makes these findings compelling is the convergence of multiple traits within single isolates. A bacterium that simultaneously fixes nitrogen, unlocks phosphorus, and secretes auxins is a candidate for multifunctional microbial inoculants—living fertilizers that could reduce the environmental footprint of coffee cultivation while lowering input costs for farmers. The authors caution that their assays represent an initial in vitro screening. Confirming true diazotrophy will require quantitative nitrogen fixation assays such as acetylene reduction or nitrogen-15 isotope dilution, molecular detection of nitrogenase genes like nifH, and ultimately greenhouse and field inoculation trials to verify agronomic performance under real conditions.

Nevertheless, the study fills an important gap. While culture-independent metagenomic studies have catalogued the vast microbial diversity of coffee plantations across Latin America, cultivable isolates remain indispensable for experimentally validating microbial functions and translating ecological knowledge into practical agricultural products. By demonstrating that both organic and conventionally managed coffee soils harbor a resilient core microbiota alongside management-specific taxa with valuable plant growth-promoting traits, the research establishes a foundation for developing microbial consortia adapted to local edaphoclimatic conditions. For an industry confronting rising fertilizer prices, nitrogen losses, and mounting environmental scrutiny, the humble bacteria of Minas Gerais may prove to be coffee’s most valuable untapped resource.

Subject of Research: Cultivable plant growth-promoting bacteria in Brazilian Coffea arabica soils under organic and conventional mineral fertilization

Article Title: Cultivable diversity and plant growth-promoting traits of free-living bacteria from coffee soils under contrasting fertilization systems

Article References: Guimarães, C. V., Velozo, T. G. R., da Luz, J. M. R., Públio, G. C., da Silva, J. P. T., Pereira, L. L., & de Cássia Soares da Silva, M. (2026). Cultivable diversity and plant growth-promoting traits of free-living bacteria from coffee soils under contrasting fertilization systems. International Microbiology. https://doi.org/10.1007/s10123-026-00893-2

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00893-2

Keywords: coffee, plant growth-promoting bacteria, nitrogen fixation, phosphate solubilization, indole-3-acetic acid, soil microbiome, organic fertilization, mineral fertilization, Coffea arabica, microbial inoculants, Brazil, sustainable agriculture

The research, published in Scientific Reports, focuses on a challenge shared by many farmers in regions where access to expensive synthetic fertilizers is limited. Onion production depends heavily on the availability of essential nutrients, particularly nitrogen, phosphorus and potassium. Yet fertilizer performance is not determined only by the amount applied. Soil structure, moisture, microbial activity, climate and the distance between plants all influence how efficiently onions convert nutrients and sunlight into leaves and bulbs. The Bonga study brings these factors together in an effort to understand how organic manure and field geometry work as a combined production system.

Chicken manure is more than a waste product. Properly handled, it contains organic matter and plant nutrients that can improve soil fertility over time. As microorganisms decompose the manure, nutrients are gradually released into the soil, making them available for uptake by plant roots. This process, known as mineralization, is influenced by temperature, moisture and the chemical composition of the manure. Nitrogen released during decomposition supports leaf growth, while phosphorus contributes to root development and energy transfer within the plant. Potassium helps regulate water movement, enzyme activity and the transport of sugars into developing bulbs.

The timing and balance of those nutrients are particularly important for onions. The crop must first establish a healthy canopy of leaves, because each leaf contributes to the photosynthetic machinery that eventually feeds the bulb. If nutrition is inadequate, the plants may remain weak and produce undersized bulbs. If nitrogen is excessive or supplied too late, onions may continue producing leaves instead of shifting efficiently toward bulb enlargement, potentially affecting maturity, storage life and quality. By examining chicken manure within an onion production system, the study addresses not only how much the crop grows, but also how nutrient release may influence the biological transition from vegetative growth to bulb formation.

Spacing adds a second layer of complexity. When onion plants are established too close together, they compete for light, water and nutrients. Dense stands can produce a larger number of bulbs per unit of land, but individual bulbs may be smaller because resources are divided among more plants. Wider spacing can reduce competition and allow each plant greater access to soil resources, potentially promoting larger bulbs. However, excessively wide spacing may leave valuable field area unused and reduce total yield even if individual onions become heavier. The most productive arrangement therefore depends on the balance between bulb size and the number of bulbs harvested.

This distinction is critical because “yield” is not a single concept in agricultural science. Researchers may assess total biological production, marketable yield, average bulb weight, bulb diameter and the proportion of onions that reach commercially desirable grades. Quality can also include attributes such as bulb firmness, uniformity, moisture content and the concentration of compounds responsible for onion flavor and pungency. These traits matter to farmers, traders and consumers in different ways. A field with the greatest total weight may not generate the highest income if much of the harvest consists of small, damaged or poorly stored bulbs.

At Bonga, the study’s experimental design is centered on comparing chicken-manure management with different distances between onion plants. Such trials allow researchers to separate the effects of fertilization from the effects of plant density and, crucially, to examine whether the two factors interact. An interaction occurs when the response to one treatment changes depending on the level of another. For example, a spacing arrangement that performs poorly in nutrient-depleted soil might become highly productive when organic matter and nutrients are improved. Conversely, applying more manure may not deliver its full benefit if plants are crowded and cannot access enough space, water or light.

The importance of this work extends beyond a single field in southwestern Ethiopia. Smallholder farmers often operate under tight financial constraints, making locally available organic inputs especially valuable. Poultry production is expanding in many agricultural communities, generating manure that can either become an environmental burden or be returned to the soil as a resource. Using it effectively could reduce dependence on purchased fertilizers, improve soil organic matter and support more circular farming systems. But manure is not automatically safe or uniform: its nutrient concentration varies, immature manure can injure roots, and poor handling may introduce pathogens or cause nutrient losses. Scientific guidance is needed to turn a readily available material into a reliable farm input.

The Bonga investigation also highlights why agricultural recommendations cannot always be transferred directly from one region to another. Onion performance is shaped by local altitude, temperature, rainfall patterns, soil texture, fertility status and farming practices. A spacing recommendation developed for one climate may not produce the same result elsewhere, just as a manure rate that works in one soil may be insufficient or excessive in another. Field-based experiments therefore provide essential evidence for location-specific production, particularly in regions where farmers must make decisions with limited irrigation, variable weather and restricted access to laboratory soil testing.

By linking a locally available fertilizer with a practical crop-management decision, the study offers a pathway toward more precise and sustainable onion production. Its central message is not simply that chicken manure can improve a field, or that spacing can change bulb size, but that these choices must be considered together. The way plants are arranged determines how efficiently they use the nutrients released into the soil, while the fertility of that soil influences how strongly plants respond to the space available to them. For Ethiopian growers and agricultural advisers, the findings could help refine recommendations aimed at producing more uniform, marketable onions without relying exclusively on costly external inputs. More broadly, the research illustrates a principle increasingly shaping modern agriculture: the future of food production may depend not on one miracle input, but on carefully engineered combinations of biology, resource recycling and field design.

Subject of Research: Chicken manure and plant spacing effects on onion yield and quality at Bonga, Ethiopia.

Article Title: Chicken manure and spacing effects on onion yield and quality at Bonga, Ethiopia.

Article References: Aga, G.W., Merga, B.B., Gitima, G. et al. “Chicken manure and spacing effects on onion yield and quality at Bonga, Ethiopia.” Scientific Reports (2026). https://doi.org/10.1038/s41598-026-65425-4

Image Credits: AI Generated

DOI: 10.1038/s41598-026-65425-4

Keywords: onion production, chicken manure, plant spacing, crop yield, bulb quality, soil fertility, organic fertilizer, Ethiopia, sustainable agriculture, Bonga.