Integrated Microdosing Selected Basal Fertilizers and Lime Modulates Fungal and Bacterial Populations in Acidic Soils under Maize Production in the Meru Highland, Kenya
Mbaka K. Felister, H. O. Ndukhu, G. O. Oloo-Abucheli, Muindi, Esther Mwende, J. K. Kiramana, Emmanuel R. Mwakidoshi
International Journal of Plant & Soil Science September 26, 2026 DOI: 10.9734/ijpss/2026/v38i106349 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Randomized complete block split-plot field experiment Peer reviewed |
|---|---|
| Population | Acidic maize-growing soils of the Kenyan highlands, sampled before the experiment and after each of two cropping seasons |
| Interventions | DAP NPK 23:23:0 calcite lime dolomitic lime farmyard manure (FYM) |
| Dose | Microdosing (MD): 7.5 t FYM ha-1, 106.0 kg DAP ha-1, 212.0 kg NPK ha-1 and 0.225 t ha-1 of either calcite or dolomitic lime (75% of recommended rates); no microdosing (NMD): 10 t FYM ha-1, 141.3 kg DAP ha-1, 282.6 kg NPK ha-1 and 0.3 t ha-1 of either calcite or dolomitic lime (100% of recommended rates) |
| Duration | Two cropping seasons: October 2024-January 2025 and March-July 2025 |
| Measures | culturable fungal and bacterial populations expressed as colony-forming units (CFU) g-1 soil, determined by serial dilution and spread-plate method |
| Topics | Microdosing |
| Key findings | Microdosing (75% of recommended fertilizer and lime rates) combined with calcite + NPK 23:23:0 + farmyard manure produced the highest culturable fungal and bacterial populations, significantly exceeding the same treatment at full rates and the untreated controls. The authors attribute the improved microbial populations to localized nutrient supply, organic carbon addition and amelioration of soil acidity, and propose microdosing as a way to improve nutrient use efficiency while supporting soil microbes in acidic maize soils. |
Abstract
The biological component of soil health, particularly bacteria and fungi, plays a central role in organic matter decomposition, nutrient cycling and mineralization, thereby contributing to the maintenance of soil fertility and overall soil functioning. However, continuous cultivation, inadequate nutrient replenishment and inappropriate fertilizer management can lead to soil degradation. Soil acidification can further constrain biological functioning by reducing microbial activity, increasing aluminium toxicity and limiting the availability of essential nutrients. Addressing these challenges requires integrated, resource-efficient soil management approaches that enhance soil fertility, support biological functioning and promote environmental sustainability. The combined use of mineral fertilizers, lime and farmyard manure (FYM), together with efficient nutrient placement through microdosing, may provide an effective approach for improving soil chemical and biological conditions. Information on the effects of fertilizer and lime microdosing on soil microbial populations, particularly bacteria and fungi, in strongly acidic maize-growing soils of the Kenyan highlands remains limited. A two-season field experiment was conducted from October 2024-January 2025 and March-July 2025 using a randomized complete block design arranged in a split-plot layout with three replications. The main-plot factor comprised microdosing (MD; 75% of recommended fertilizer and lime rates) and no microdosing (NMD; 100%), while the subplots comprised eighteen (18) fertilizer and lime treatments involving DAP, NPK 23:23:0, calcite lime, dolomitic lime, FYM, their combinations and a control, replicated three times, giving 108 experimental units. Under no microdosing (NMD), all inputs were applied once at 100% of the recommended rates: 10 t FYM ha⁻¹, 141.3 kg DAP ha⁻¹, 282.6 kg NPK ha⁻¹ and 0.3 t ha⁻¹ of either calcite or dolomitic lime. Under microdosing (MD), inputs were applied at 75% of the recommended rates: 7.5 t FYM ha⁻¹, 106.0 kg DAP ha⁻¹, 212.0 kg NPK ha⁻¹ and 0.225 t ha⁻¹ of either calcite or dolomitic lime. Soil sampling and analysis were conducted before the experiment and after each cropping season. Culturable fungal and bacterial populations were determined using the serial dilution and spread-plate method and expressed as colony-forming units (CFU) g⁻¹ soil. Data were log₁₀-transformed before pooled split-plot ANOVA, and significant means were separated using Tukey's Honestly Significant Difference (HSD) test at 5%. Pooled analysis of variance showed that microdosing significantly affected both fungal and bacterial populations (P < 0.01), while the microdosing × treatment interaction was also highly significant for both fungal and bacterial populations (P < 0.001). The highest fungal population was recorded under MD with calcite + NPK 23:23:0 + FYM, with 1.36 × 10⁷ CFU g⁻¹ soil (Log₁₀ = 7.134) in Season 1 and 1.41 × 10⁷ CFU g⁻¹ soil (Log₁₀ = 7.149) in Season 2. These values were significantly higher (P < 0.05) than the corresponding NMD treatment, which recorded 1.28 × 10⁷ CFU g⁻¹ soil (Log₁₀ = 7.107) and 1.33 × 10⁷ CFU g⁻¹ soil (Log₁₀ = 7.124) in Seasons 1 and 2, respectively. The highest bacterial populations were similarly recorded under MD with calcite + NPK 23:23:0 + FYM, reaching 1.89 × 10⁸ CFU g⁻¹ soil (Log₁₀ = 8.276) in Season 1 and 1.95 × 10⁸ CFU g⁻¹ soil (Log₁₀ = 8.289) in Season 2. These were significantly higher (P < 0.05) than the corresponding NMD values of 1.81 × 10⁸ CFU g⁻¹ soil (Log₁₀ = 8.258) and 1.84 × 10⁸ CFU g⁻¹ soil (Log₁₀ = 8.264), respectively. The controls consistently recorded the lowest microbial populations. For fungi, the MD and NMD controls recorded 3.97 × 10⁶ and 4.00 × 10⁶ CFU g⁻¹ soil (Log₁₀ = 6.598 and 6.602) in Season 1 and 4.00 × 10⁶ and 4.07 × 10⁶ CFU g⁻¹ soil (Log₁₀ = 6.602 and 6.609) in Season 2 with the two control treatments reported as statistically similar (P < 0.05). The results demonstrate that combining microdosing with calcite, NPK 23:23:0 and FYM enhanced culturable fungal and bacterial populations compared with both the corresponding NMD treatment and the untreated controls. The improved microbial populations were likely associated with localized nutrient supply, organic carbon addition and amelioration of soil acidity. Microdosing therefore has potential to improve nutrient use efficiency while creating favourable conditions for soil microbial proliferation in acidic maize growing soils.
Comparable studies
Other randomized controlled trials on microdosing, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Use of microdosing to predict pharmacokinetics at the therapeutic dose: Experience with 5 drugs Volunteers | 2006 | Crossover study | |
| Self-blinding citizen science to explore psychedelic microdosing. Participants who microdose psychedelics | 2021 | Self-blinding citizen science initiative with placebo control | n = 191 |
| Microdosing with psilocybin mushrooms: a double-blind placebo-controlled study Individuals starting to microdose with psilocybin mushrooms (Psilocybe cubensis) | 2022 | Double-blind placebo-controlled experimental design | n = 34 |
| Preliminary Report on the Effects of a Low Dose of LSD on Resting-State Amygdala Functional Connectivity. Healthy young adults, 18 to 35 years old | 2019 | Randomized controlled trial | n = 20 |
| Acute Mood-Elevating Properties of Microdosed Lysergic Acid Diethylamide in Healthy Volunteers: A Home-Administered Randomized Controlled Trial. Healthy male volunteers | 2023 | Randomized controlled trial | n = 80 |