Zinc oxide nanoparticles boost shallot yields in semi-arid field trials

Zinc oxide nanoparticles have outperformed conventional zinc sulfate fertilizer in a rare multi-site field test of nano-fertilizer chemistry, raising bulb yields of a semi-arid-adapted shallot by more than half compared with untreated crops. The one-year trial, conducted at two locations in Isfahan Province, Iran, found that foliar and bulb-priming applications of zinc oxide nanoparticles at 450 milligrams of zinc per liter lifted bulb yield by 57 to 61 percent over the untreated control and by 18 to 27 percent over an ionic zinc sulfate treatment applied at 900 milligrams of zinc per liter. The study, published in the journal Bioscience Nanotechnology, is among the relatively few evaluations of nano-scale zinc fertilizers carried out under realistic open-field conditions rather than in greenhouses, pots, or hydroponic systems.

The crop at the center of the experiment was shallot (Allium hirtifolium Boiss.), a perennial member of the Amaryllidaceae family cultivated widely across Asia and the Middle East. The plant is valued not only as a food but also for its content of vitamins, micronutrients, organosulfur compounds, flavonoids, and phenolics, compounds that have been associated in the literature with reduced risks of cardiovascular disease, diabetes, and several cancers. Like many crops grown on calcareous soils, shallot is frequently limited by zinc availability. In alkaline soils with a pH above 7.5, zinc rapidly precipitates, adsorbs onto clay minerals, or complexes with organic matter, leaving crops deficient even when total soil zinc is adequate. Conventional zinc sulfate suffers from the same chemistry: ionic zinc is immobilized shortly after soil application, cutting nutrient use efficiency and driving up fertilizer inputs.

Nanoparticles offer a different delivery profile. Because of their nanoscale dimensions and high surface-area-to-volume ratio, zinc oxide nanoparticles adhere to and penetrate leaf surfaces through stomatal and cuticular pathways more effectively than dissolved ions, and they dissolve more slowly, potentially sustaining zinc release through critical growth stages. The researchers tested this proposition in the field using bulbs of the Fereydounshahr ecotype supplied by local farmers. The nanoparticles, purchased from Nanosany in Iran, were characterized before use: electron microscopy confirmed a mean particle size of 20 nanometers with a distribution of 20 to 30 nanometers, dynamic light scattering gave a mean hydrodynamic diameter of roughly 100 nanometers and a zeta potential of minus 45 millivolts, and X-ray diffraction confirmed crystallinity and purity.

The field design was deliberately simple but geographically contrasted. Two semi-arid sites with different soils hosted simultaneous, one-year randomized complete block experiments with three replicates and six plants per treatment. Zardfahreh, at 2,391 meters elevation, has sandy loam soil with lower organic carbon and higher electrical conductivity; Bonehkamar, at 2,524 meters, has clay loam soil with higher organic carbon and lower electrical conductivity. Bulbs were planted in late October 2023 and grown through October 2024. Each treatment combined bulb priming with one milliliter of solution per bulb and a foliar spray of two milliliters per plant at 194 days after planting, a stage chosen because nutrient demand, photosynthetic activity, and assimilate translocation are all elevated as the crop moves from vegetative growth into bulb development. Treatments comprised 50, 150, and 450 milligrams of zinc per liter as nanoparticles, 900 milligrams of zinc per liter as zinc sulfate, and a distilled-water control.

The physiological results were consistent across both sites. Chlorophyll-a rose by 37 to 63 percent over control with increasing nanoparticle concentration, and by 29 to 47 percent with zinc sulfate; at the highest nanoparticle rate, chlorophyll-b exceeded the sulfate treatment by 71 percent at Bonehkamar and 116 percent at Zardfahreh. Carotenoids, the accessory pigments that protect the photosynthetic apparatus from excess light, climbed by 37 to 114 percent over control at Bonehkamar and by a striking 206 percent at Zardfahreh under the 450 milligram per liter nanoparticle treatment. Leaf relative water content, a measure of plant hydration under water-limited conditions, increased by 12 to 19 percent with the highest nanoparticle dose compared with control and sulfate treatments, suggesting improved osmotic regulation and water retention.

Those biochemical gains translated into measurable growth. Plants receiving the highest nanoparticle dose stood 41 to 50 percent taller than controls and 11 to 20 percent taller than sulfate-treated plants, and carried up to 8.2 leaves per plant at Bonehkamar compared with 3.2 to 4.3 leaves under control and sulfate treatments. Leaf fresh weight rose by up to 56 percent over the sulfate treatment, sister bulb counts per plant increased by as much as 250 percent over sulfate at Bonehkamar, and bulb diameter grew in a dose-dependent fashion, measuring 7 to 33 millimeters larger than sulfate-treated bulbs at Bonehkamar and 3 to 21 millimeters larger at Zardfahreh. The yield peak came at Bonehkamar, where the 450 milligram per liter nanoparticle treatment produced 18.66 megagrams per hectare, against 16.03 megagrams per hectare at Zardfahreh.

Bulb quality changed as well. Total phenol content rose by 77 to 103 percent over control at Bonehkamar and 39 to 66 percent at Zardfahreh, and exceeded sulfate treatments by 35 to 54 percent and 20 to 42 percent respectively. Flavonoid levels peaked at 2 and 1.5 milligrams quercetin equivalents per gram at the two sites under the highest nanoparticle dose. Antioxidant activity, measured with a DPPH free-radical assay on methanol extracts of bulb tissue, increased by 1.1 to 28 percent over sulfate treatment at Bonehkamar and by 20 percent at Zardfahreh at the highest dose. Bulb zinc concentration, quantified by inductively coupled plasma optical emission spectrometry, rose by 261 percent over control at Bonehkamar and 160 percent at Zardfahreh with the top nanoparticle rate, although the sulfate treatment raised bulb zinc to statistically similar levels, indicating that both formulations biofortify the crop effectively.

Transmission electron microscopy of leaf tissue offered a cellular-scale view of the response. Control plants showed thin cell walls, long elongated chloroplasts with compact grana, and large mitochondria. Nanoparticle-treated plants instead displayed shorter, wider chloroplasts, thicker cell walls, more starch granules and plastoglobules distributed on the grana surface, and no visible mitochondrial changes. Electron-dense structures appeared within cell walls and chloroplasts, hinting at nanoparticle uptake and translocation into leaf tissues, but the authors could not confirm elementally that these structures contained zinc, because energy-dispersive X-ray analysis was not available. The team proposes that improved foliar adhesion, gradual zinc release, and enhanced intracellular zinc availability explain why the nanoparticles outperformed the ionic fertilizer, possibly aided by phloem-mediated redistribution of foliar-absorbed zinc into developing bulbs.

The two sites also revealed how strongly environment shapes nano-fertilizer performance. Responses were consistently stronger at Bonehkamar, which the authors attribute to its higher organic carbon, lower salinity, and clay loam texture, whereas reduced organic matter, elevated salinity, and cooler seasonal temperatures at Zardfahreh likely constrained nutrient availability and metabolic activity. The authors note that nanoparticle effects are concentration-dependent, and that excessive accumulation can induce oxidative damage and phytotoxicity under some conditions, making dose optimization essential. Statistical analysis detected moderate variance heterogeneity between sites, which the researchers judged acceptable given the balanced design and equal group sizes.

The study’s scope carries clear limits: it covers a single growing season, one ecotype, and two Iranian locations, and the mechanistic claims about foliar penetration and sustained release rest partly on prior literature rather than direct measurement in this crop. The authors themselves flag the unresolved identity of the electron-dense intracellular structures and call for further work on terpenoid biosynthesis and the molecular basis of nanoparticle-plant interactions. Even so, the trial adds field-scale evidence to a growing body of greenhouse and pot studies suggesting that nano-scale zinc formulations can couple biofortification with improved photosynthetic performance, water status, and secondary metabolism.

Subject of Research: Field testing of zinc oxide nanoparticle fertilizer effects on shallot growth, physiology, and yield in semi-arid soils

Article Title: Multi-site field validation of improved morpho-physiological responses and yield in Allium hirtifolium with zinc oxide nanoparticle treatments in semi-arid soils

Article References: Moguee, S., Fallah, S., Pokhrel, L. R., Adavi, Z., & Berkuta, J. (2026). Multi-site field validation of improved morpho-physiological responses and yield in Allium hirtifolium with zinc oxide nanoparticle treatments in semi-arid soils. Bioscience Nanotechnology, 2(1), Article 26. https://doi.org/10.1186/s44331-026-00032-8

Image Credits: AI Generated

DOI: 10.1186/s44331-026-00032-8

Keywords: zinc oxide nanoparticles, nanofertilizer, shallot, Allium hirtifolium, semi-arid agriculture, zinc biofortification, chlorophyll, antioxidant activity, bulb yield, foliar application, calcareous soil, field trial