Waste mica plus bacteria unlocks potassium in alluvial and black soils

Potassium is the quiet workhorse of agriculture. It is the second most abundant element in plant tissues, driving enzyme activation, protein synthesis, photosynthesis, nutrient transport, osmoregulation, and stress tolerance, yet it is chronically underapplied compared with nitrogen and phosphorus, especially in developing countries where imported potash is expensive and domestic deposits are scarce. A new 60-day incubation study from Rajasthan, published in Discover Soil, reports that a bacterium called Enterobacter wuhouensis, working alongside farmyard manure and waste mica, can substantially raise the amount of plant-available potassium in two contrasting Indian soils. The combination of 75 percent mica and 25 percent farmyard manure inoculated with the potassium-solubilizing strain reached 322.67 kilograms of available potassium per hectare in alluvial soil and 398.00 kilograms per hectare in black soil at 60 days, the highest values recorded across all treatments.

The problem the researchers set out to address is both chemical and economic. India has no high-grade potassium mineral deposits and relies heavily on imported muriate of potash, which supplies readily soluble but transient potassium that is prone to leaching losses. A nationwide survey of 371 Indian districts found that roughly 21 percent of soils are low in potassium and 51 percent have medium availability, indicating widespread deficiency. Meanwhile, India is one of the world’s largest mica producers, and districts such as Munger and Koderma generate substantial waste mica during mining and processing. This discarded material contains 8 to 12 percent potassium oxide, and the mica used in the experiment itself measured 8.91 percent total potassium, but its low solubility has long restricted direct agronomic use because the nutrient remains locked inside mineral structures unavailable for immediate plant uptake.

Only a tiny fraction of soil potassium is actually accessible to crops. The water-soluble and exchangeable forms together constitute less than 2 percent of total soil potassium, while the vast majority is fixed within mineral lattices. Certain microorganisms, however, can tap this mineral-bound reservoir by producing organic acids and other biochemical agents. Bacteria such as Bacillus mucilaginosus, Paenibacillus species, and Pseudomonas species have recognized potassium-solubilizing potential, and the fungus Aspergillus niger has been reported to extract potassium from feldspar and mica under both laboratory and field conditions. The strain deployed here, KSB-13 (Enterobacter wuhouensis), was obtained from the Department of Molecular Biology and Biotechnology at Maharana Pratap University of Agriculture and Technology in Udaipur and applied at 650 milliliters per hectare.

The experimental design was deliberately comparative. Alluvial soil was collected from the bank of the Banas River in Chittorgarh District of Rajasthan, and black soil came from the southern part of the same district. The alluvial soil had a sandy loam texture, a water-holding capacity of 42 percent, a slightly alkaline pH, low electrical conductivity, medium available nitrogen, phosphorus, and potassium, and low iron. The black soil was a clayey loam with a 52 percent water-holding capacity, slightly alkaline pH, medium electrical conductivity, medium available nutrients, and low iron. Both soils were air-dried, sieved through a 2-millimeter sieve, and incubated at 28 plus or minus 2 degrees Celsius with moisture maintained at roughly 60 percent of water-holding capacity. A completely randomized design with nine treatments and three replications varied the proportions of mica and farmyard manure on a potassium contribution basis equivalent to 60 kilograms of potassium oxide per hectare, with and without the bacterial inoculant.

The treatment structure ranged from a control through combinations of 25, 50, 75, and 100 percent mica with farmyard manure, each also tested with the added solubilizer. Farmyard manure analyzed at 1.0 percent total nitrogen, 0.42 percent total phosphorus, and 0.81 percent total potassium, providing both a nutrient substrate and an organic carbon source for microbial metabolism. The researchers measured soil pH, available potassium extracted with ammonium acetate and quantified by flame photometry, microbial populations by the dilution plate technique on selective media, dehydrogenase enzyme activity using triphenyl tetrazolium chloride reduction, and potassium-solubilizing power in liquid Aleksandrov medium, where sterilized and non-sterilized soils were compared to isolate the microbial influence on soluble potassium release.

Available potassium rose significantly in both soils, with black soil showing more pronounced increases attributed to its higher cation exchange capacity. The control treatment showed minimal variation over the 60 days, while the inoculated treatments consistently achieved higher potassium levels, peaking in the 75 percent mica plus 25 percent manure plus solubilizer combination at 322.67 kilograms per hectare in alluvial soil and 398.00 kilograms per hectare in black soil. The critical difference values confirmed these differences were statistically significant. The authors caution, however, that a strong correlation between the solubilizers and available potassium does not by itself establish causation, since soil texture, cation exchange capacity, manure quality, and indigenous microflora all likely contributed to the observed trends alongside the applied bacterium.

Soil pH told a parallel story about mechanism. Treatments with farmyard manure produced a progressive pH reduction, with the sharpest decline in alluvial soil, where the inoculated treatment reached pH 6.81 at 60 days, while black soil showed a more moderate drop to pH 7.45. The researchers attribute this difference to the alluvial soil’s lower clay content and cation exchange capacity, which left it more susceptible to pH change, whereas the black soil’s higher clay content and buffering capacity dampened the acidification. The acidification itself matters because microbial decomposition of organic matter releases organic acids such as citric and acetic acids, and the solubilizing bacterium accelerates the process by producing low-molecular-weight acids, including gluconic, citric, and oxalic acids, that dissolve mica interlayers and release potassium ions from the mineral lattice.

Microbial dynamics responded dramatically to the integrated amendments. Bacterial counts peaked at 50.00 times ten to the sixth colony-forming units per gram in alluvial soil and 123.30 times ten to the sixth in black soil, representing 146 percent and 228 percent increases in inoculated treatments. Fungal populations in black soil rose by 250 percent, actinomycetes increased by 45 percent in alluvial and 67 percent in black soils, and the solubilizing bacterium’s own population climbed to 55.33 times ten to the fourth colony-forming units per gram in alluvial soil and 75.00 times ten to the fourth in black soil in the top treatment. Dehydrogenase activity, a key indicator of microbial oxidative metabolism measured as micrograms of triphenyl formazan per gram of soil per hour, reached 25.34 in alluvial soil and 75.33 in black soil in the same treatment, compared with baseline values of 17 and 23 respectively, while potassium-solubilizing power peaked at 9.77 micrograms of potassium per 0.03 milligrams of soil in black soil.

The authors propose five parallel mechanisms to explain the steady potassium release. Acidification from bacterial organic acids dissolves the mica interlayers. Chelation by those acids binds iron and aluminum ions, displacing potassium ions into solution. Enzymatic stimulation, particularly through dehydrogenase, promotes microbial metabolism and nutrient turnover. Carbon mineralization from microbial respiration generates carbonic acid that accelerates mineral breakdown. Finally, surface complexation, in which microbial exudates adsorb to mineral surfaces and alter surface charge, enhances mica weathering. Unlike conventional muriate of potash, which delivers a transient soluble pulse, this bio-solubilization approach promotes slow, sustained release that reduces leaching losses while recycling locally available mica waste and manure and supporting soil biological health.

The black soil outperformed the alluvial soil across nearly every measure, a contrast the researchers link to its superior clay content, moisture retention, organic matter, and cation exchange capacity, which provided a more favorable environment for microbial colonization and nutrient cycling. The alluvial soil’s sandier texture, reduced microbial habitat, and lower buffering capacity explain its weaker response, underscoring that the effectiveness of potassium solubilizers is not uniform but shaped by soil physicochemical properties. The findings suggest that integrating potassium-solubilizing bacteria with waste mica and farmyard manure offers a viable, eco-friendly, and low-cost route to enhance soil potassium availability, but the study was conducted under controlled laboratory conditions, and the authors state plainly that field-level efficacy, long-term effects on soil health, and economic viability remain to be validated through field-scale experiments before this integrated strategy can be recommended for potassium-deficient regions.

Subject of Research: Microbial and organic enhancement of potassium mineralization from waste mica in alluvial and black soils

Article Title: A comparative assessment of potassium mineralization from waste mica by application of potassium solubilizers and FYM in alluvial and black soils

Article References: Sani, S., Bairwa, R., Abdulkadir, A. I., Lawal, A. U., Gurjar, O. P., Regar, C. L., Meena, V. S., & Alhassan, S. (2026). A comparative assessment of potassium mineralization from waste mica by application of potassium solubilizers and FYM in alluvial and black soils. Discover Soil, 3(1), Article 96. https://doi.org/10.1007/s44378-025-00120-w

Image Credits: AI Generated

DOI: 10.1007/s44378-025-00120-w

Keywords: potassium solubilization, waste mica, Enterobacter wuhouensis, farmyard manure, alluvial soil, black soil, dehydrogenase activity, soil incubation, potassium availability, sustainable agriculture, soil microbiology, organic acids