The study, carried out by Habtamu Admas and Tesfahun Kassahun of Injibara University and published in Environmental Earth Sciences, tested two complementary strategies for reclaiming salt-affected soils across two experimental sites in Asaita District, roughly 670 kilometers northeast of Addis Ababa. The first strategy was biological: growing salt-tolerant forage species, alone and in combination with filter-cake compost, a byproduct of sugar processing rich in organic matter and nutrients. The second was chemical-organic: applying gypsum, a calcium sulfate mineral, at rates of zero, five, and ten tonnes per hectare, factorially combined with the same compost rates. Both experiments were laid out in randomized complete block designs with three replications, producing 54 plots in total under genuine farmers’ field conditions rather than the more forgiving environment of a research station.

The chemistry behind the approach is elegantly simple. Salinity, measured as electrical conductivity, reflects the concentration of soluble salts, chiefly chlorides and sulfates of sodium, calcium, and magnesium, that raise the osmotic stress on plants and impair their ability to take up water. Sodicity is a different problem altogether: an excess of sodium ions clinging to the soil’s cation-exchange sites, where they cause clay particles to disperse, aggregates to collapse, and water infiltration to grind to a halt. Gypsum attacks the sodic half of the problem directly. When it dissolves, its calcium ions swap places with sodium on the exchange complex, releasing sodium into the soil solution, where a well-managed irrigation and drainage system can flush it below the root zone. Compost, meanwhile, works on the physical side, feeding microbes, building aggregates, improving porosity, and releasing its own basic cations that help displace sodium.

The results at the second experimental site, where baseline conditions were more severely degraded with an electrical conductivity of 7.1 decisiemens per meter and an exchangeable sodium percentage of 19.2 percent, delivered the study’s most striking numbers. The combined application of ten tonnes per hectare of gypsum and ten tonnes per hectare of filter-cake compost reduced electrical conductivity from 6.56 to 2.85 decisiemens per meter, a drop of 56.6 percent, and cut the exchangeable sodium percentage from 13.17 to 5.79 percent, a reduction of 56.0 percent. Soil pH fell by 0.60 units, from 8.25 to 7.65, pushing the soil out of strongly alkaline territory. Exchangeable sodium dropped from 9.64 to 4.61 centimoles of charge per kilogram, and bulk density, a key indicator of soil compaction, fell from 1.37 to 1.01 grams per cubic centimeter, signaling a soil that had reopened its pore spaces to water and roots.

Just as importantly, the integrated treatment improved the soil’s capacity to hold and exchange nutrients. Cation exchange capacity, a measure of the soil’s ability to retain positively charged nutrients, rose from 73.2 to 79.6 centimoles of charge per kilogram under the combined gypsum-compost treatment. Total nitrogen, organic carbon, available phosphorus, and available sulfur all increased relative to the untreated control, and extractable micronutrients including iron, manganese, zinc, copper, and boron rose in parallel, a critical finding in alkaline soils where these elements are often locked away from plant roots. The authors attribute these gains to the mineralization of nutrients from the compost by soil microbes and to the improved root environment created as sodium was displaced and leached.

At the first experimental site, where the biological approach was tested, Blue panic grass (Panicum antidotale) combined with ten tonnes per hectare of compost proved the standout performer, producing the lowest bulk density at 1.01 grams per cubic centimeter and the lowest pH at 7.77, compared with 1.31 grams per cubic centimeter and 8.32 in the untreated control. Plots planted with Sesbania sesban and the same compost rate recorded the lowest electrical conductivity among the forage treatments, at 3.17 decisiemens per meter against 9.5 in the control, alongside the lowest exchangeable sodium percentage at 6.29 percent. The mechanism is part extraction and part facilitation: deep-rooted, salt-tolerant plants absorb sodium and other salt ions through their tissues, while their roots and the decomposing compost open channels for water to move dissolved salts downward, out of the root zone.

The broader context makes these findings more than an academic curiosity. Soils developed from volcanic and lacustrine deposits in the Awash valley include substantial areas of Solonetz, Solonchaks, and other salt-affected units, and agriculture in Asaita depends almost entirely on irrigation because rainfall is too erratic to support reliable rain-fed cropping. Mean monthly evapotranspiration in the area ranges from 222 millimeters in November to 375 in July, a relentless evaporative pump that concentrates salts at the soil surface. In a region where roughly 90 percent of the Afar population depends on livestock and small-scale irrigated cropping along river basins, each hectare lost to salinity directly undermines household income and regional food security. The forage-based reclamation route carries a bonus: the grasses and legumes themselves become fodder for penned animals, turning a remediation cost into a source of income.

The study is also candid about its limits. The researchers calculated gypsum requirements using a standard formula based on cation exchange capacity, actual and target exchangeable sodium percentages, bulk density, and reclamation depth, applying rates appropriate to the upper 30 centimeters of soil. Adequate drainage was maintained throughout, which the authors stress is essential; without it, the sodium displaced by gypsum would simply accumulate again. They note that available phosphorus actually declined at the highest gypsum rates, likely because abundant calcium ions react with phosphate to form less-soluble calcium phosphate compounds, a trade-off that farmers and agronomists will need to manage. The irrigation water’s own electrical conductivity and sodium adsorption ratio were not recorded, and no combined statistical analysis across the two sites was possible because the experiments had different treatment structures.

Perhaps the most important caveat concerns scale. The authors explicitly warn that the findings should not be generalized to the entire Afar Region, since soil properties, irrigation conditions, and agro-ecological characteristics vary considerably from place to place. They also flag that the economic assessment in the study is qualitative rather than a formal cost-benefit analysis, and that the viability of hauling gypsum and compost to remote fields will depend on local prices, transport distances, and labor. Still, both raw materials have appealing characteristics: filter cake is an agro-industrial residue that would otherwise require disposal, it contains 1.5 to 2.0 percent nitrogen, 0.8 to 1.2 percent available phosphorus, and 1.2 to 1.8 percent potassium with a favorable carbon-to-nitrogen ratio, and its low electrical conductivity and near-neutral pH make it safe for use on already salt-stressed land.

For a world losing farmland to salt at an accelerating pace as irrigation expands and climates dry, the Asaita results offer a concrete, field-verified recipe: where salinity and sodicity co-occur, neither gypsum alone nor compost alone is enough, but ten tonnes per hectare of each, applied together under sound irrigation and drainage, can push a degraded saline-sodic soil back toward productivity within a single growing season. The recommendation carries a condition, not a promise. It works where water can be applied in the right amounts and drained away, carrying the displaced sodium with it. In the Lower Awash Basin, where the river supplies the water and the desert supplies the heat, that combination of chemistry, biology, and careful water management may be the most practical lifeline available to the farmers watching their fields turn white.

Subject of Research: Field evaluation of gypsum and compost amendments for reclaiming saline-sodic soils in Asaita District, Northeastern Ethiopia

Article Title: Application of compost and gypsum to improve physicochemical properties of saline-sodic soil conditions in Asaita District, Northeastern Ethiopia

Article References: Admas, H., & Kassahun, T. (2026). Application of compost and gypsum to improve physicochemical properties of saline-sodic soil conditions in Asaita District, Northeastern Ethiopia. Environmental Earth Sciences, 85(16), Article 408. https://doi.org/10.1007/s12665-026-13143-5

Image Credits: AI Generated

DOI: 10.1007/s12665-026-13143-5

Keywords: soil salinity, sodicity, gypsum, compost, saline-sodic soil, soil reclamation, phytoremediation, Lower Awash Basin, Ethiopia, soil physics, soil chemistry, irrigated agriculture

The scale of the underlying waste problem in Uganda provides essential context for the results. The country’s eleven major cities are home to roughly 5.5 million residents and visitors, about 12.1 percent of the national population, and this urban concentration has driven a sharp rise in solid waste generation. Kampala Capital City alone produces approximately 28,000 tons of municipal solid waste every month, a figure that has more than doubled over the past two decades. Globally, the World Bank projects that waste generation could reach 27 billion metric tons per year by 2050, and developing countries with limited collection infrastructure and low recycling rates face the steepest challenges. In Uganda, the waste stream is dominated by food scraps, paper, cloth, plastic bags and bottles, glass, medical waste, and metals, with plastics accumulating across all landfills in forms that include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polycarbonate, polyurethane, and polyvinyl chloride.

Composting has been embraced as a practical response to this mounting waste burden. By converting biodegradable material into nutrient-rich manure, composting reduces waste volume, recycles organic matter back into farmland, lessens dependence on commercial fertilizers, and improves soil quality. The technology adopted at Ugandan landfill sites is conventional and simple, consisting mainly of open windrows in which mixed waste is left to decompose. The trouble is that very little of the incoming waste is segregated. Only three of the eleven sites studied, Mukono, Lira, and Fort Portal, perform any manual pre-treatment to remove non-compostable materials before composting begins, and even that removal is incomplete. When plastic-laden mixed waste enters the windrows, mechanical weathering, oxidation, and photocatalytic breakdown progressively fragment the larger plastic items into microplastics, defined as synthetic polymer particles smaller than 5,000 micrometers.

To quantify this contamination, the research team designed a sampling campaign that controlled for both spatial and temporal variability. All samples were collected during a single two-week window in the dry season of June 2025. At each site, three mature compost piles were independently sampled, with each pile divided into top, middle, and bottom sections sampled at a depth of 5 to 15 centimeters using a stainless-steel shovel. The sections were homogenized, and material from the three piles was combined into a single composite sample of 300 grams per site, which was then sieved through a 5-millimeter stainless-steel mesh, sealed in airtight paper bags, and transported in a cool box to the laboratory. Compost maturity was verified before analysis: every sample exceeded a germination index of 70, showed a carbon-to-nitrogen ratio below 20, total nitrogen below 3.0 percent dry weight, and a pH between 7 and 9, confirming that the material analyzed was genuinely finished compost rather than raw waste.

The laboratory extraction followed an adapted wet peroxide oxidation protocol. Twenty grams of sieved, oven-dried compost were digested with Fenton reagent, a mixture of 20 milliliters of 30 percent hydrogen peroxide and 20 milliliters of 0.05 molar acidified ferrous sulphate, heated to approximately 75 degrees Celsius in a laminar flow fume hood until the organic matter disappeared. Density separation followed, using a saturated zinc chloride solution at 700 grams per liter with a density of 1.7 grams per cubic centimeter. After an hour of settling, the supernatant was filtered through a glass microfiber filter with an 11-micrometer pore size, and the captured particles were air-dried for three to four days before examination under a ZEISS Stemi 508 stereomicroscope fitted with an Axiocam 208 color camera. The researchers distinguished genuine plastic from natural particles using the hot needle and break tests, and rigorous quality controls, including blank tests with distilled water, non-plastic sampling equipment, cotton lab clothing, and glassware cleaned three times with distilled water, confirmed that no contamination was introduced during handling. Statistical comparisons across sites used a one-way ANOVA followed by Tukey’s HSD test at a significance threshold of 0.05.

The results painted a picture of pervasive but uneven contamination. Hoima’s compost site exhibited the highest microplastic abundance, more than double the eleven-site average, and was identified as a statistical outlier, significantly exceeding Jinja (p = 0.030), Mbale (p = 0.013), Soroti (p = 0.012), Kabale (p = 0.010), and Fort Portal (p = 0.0027). Jinja, which deploys an advanced Komptech Cribus 3800 mobile screening machine for post-composting processing, recorded a high abundance of 3,050 ± 304.63 particles per kilogram with relatively low variation, suggesting that mechanical screening without upstream segregation may actually break plastics down further and distribute them through the compost. At the low end, Mukono (1,250 ± 312.77 particles/kg) and Kasese (1,300 ± 316.58 particles/kg) showed statistically indistinguishable levels (p = 0.86), while Gulu and Hoima displayed the greatest variability, pointing to intermittent plastic inputs. The Ugandan average sits close to figures reported elsewhere: 2,400 ± 358 particles per kilogram in rural domestic waste compost in Zhejiang Province, China, and 2,800 ± 616 particles per kilogram in municipal organic waste compost in the Netherlands.

Perhaps the most telling result concerned particle shape. Fibres dominated at every site, accounting for 54.98 percent of all identified microplastics, followed by pellets at 15.37 percent, fragments at 15.15 percent, films at 6.06 percent, filaments at 5.41 percent, and foams at just 3.03 percent. Fibrous particles are strongly associated with synthetic textiles, ropes, and sacks, and Soroti’s profile was almost entirely fibrous, suggesting a single dominant source such as woven packaging material. Pellets, which are industrially manufactured primary microplastics often used in personal care products, featured prominently in Jinja, Fort Portal, Gulu, and Mbale. Fragments arise from the degradation of hard plastics such as high-density polyethylene, while films trace back to plastic bags and food packaging. The overwhelming presence of secondary microplastics, particles formed by the breakdown of larger plastic items, led the authors to conclude that poor waste management and inadequate segregation practices are the root cause of the contamination, rather than any single industrial source.

The environmental implications extend well beyond the compost pile itself. Previous research has shown that microplastics alter soil physical properties, including porosity, water-holding capacity, structure, and bulk density, and that polypropylene additions to loess soils can raise concentrations of nitrogen, phosphorus, and dissolved organic matter. Microplastic surfaces also adsorb hydrophobic organic compounds and heavy metals, acting as vectors that transport toxic chemicals through soil, and they can host distinct microbial communities that facilitate the spread of pathogens. Because compost is applied directly to farmland, the particles it carries enter the soil-plant system, where they may influence crop growth rates and nutrient uptake. Studies in both China and Europe have further demonstrated that the composting process itself can increase microplastic abundance by fragmenting larger plastics, with one study recording a rise from 5,133 particles per kilogram in raw material to as much as 11,200 particles per kilogram in finished compost, which helps explain why even screened compost retains substantial plastic loads.

The human health dimension adds urgency to the findings. Microplastics in compost can enter the food chain, and growing research interest now focuses on how these particles are absorbed, distributed, metabolized, and excreted in the human body. Continuous exposure has been linked to inflammation, and microplastics are suspected of interfering with metabolic processes. The authors of the Ugandan study acknowledge important limitations, including the compositing of three piles into a single site-level sample, which prevented assessment of within-site variability, the reliance on stereomicroscopy and the heated needle test rather than advanced techniques such as micro-Raman spectroscopy, FTIR, or pyrolysis-GC/MS for polymer verification, and the absence of recovery-efficiency testing. They also note the lack of standardized protocols for microplastic sampling and extraction. Even so, the central message is unambiguous: compost from municipal solid waste sites across Uganda is considerably contaminated with microplastics, and the most effective remedy lies upstream. Enhancing source segregation at the household and municipal levels, the researchers argue, would reduce the plastic entering composting facilities in the first place and lower microplastic concentrations in the final product applied to the nation’s farmland.

Subject of Research: Microplastic contamination of compost produced from municipal landfill waste in Uganda

Article Title: Identification and quantification of microplastics in compost from municipal landfills in Uganda

Article References: Tumwebaze, A., Twinomujuni, D., Baluku, E., Ogwal, F. S., Akankwasah, B., & Komakech, R. (2026). Identification and quantification of microplastics in compost from municipal landfills in Uganda. BMC Environmental Science, 3(1), Article 22. https://doi.org/10.1186/s44329-026-00064-8

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00064-8

Keywords: microplastics, compost, Uganda, municipal solid waste, landfills, waste management, soil contamination, food chain, plastic pollution, composting, environmental science, zinc chloride density separation