Zn and Cu accumulation in bulb onion (Allium cepa L.) under different mineral fertilization regimes on grey forest soils

Abstract

Purpose. To assess the effect of mineral fertilizers (ammonium nitrate, potassium chloride, single superphosphate, and the combined fertilization N60P60K90) on zinc and copper accumulation in bulb onion (Allium cepa L.), cv. Radar, grown on grey forest soils. Methods. A field experiment was conducted in 2024–2025 within a vegetable crop rotation of the Right-Bank Forest-Steppe on grey forest soils using a randomized design with four replications (five treatments: unfertilized control, N60 (ammonium nitrate), K90 (potassium chloride), P60 (single superphosphate) and N60P60K90). Planting was performed in autumn at a 45 × 6 cm spacing, top-dressing was applied at the three-true-leaf stage and at the onset of bulb formation. Soil samples were collected by the envelope method from a depth of 22–24 cm, while plant samples were taken using the point sampling method. The Zn and Cu contents in onion were determined by atomic absorption spectrophotometry the accumulation coefficient and hazard coefficient were calculated according to DSTU 3234-95.
Results. The study showed that in all fertilized treatments, the Zn content in onion was slightly higher than in the control: by 1.1% under N60, 7.0% under K90, 3.5% under P60, and 7.0% under N60P60K90. The measured Zn concentrations ranged from 1.70 to 1.82 mg/kg with an MPC of 10 mg/kg, while Cu ranged from 0.25 to 0.49 mg/kg with an MPC of 5 mg/kg. Application of ammonium nitrate reduced Cu content by 26.5%, whereas K90, P60, and N60P60K90 increased Cu content by 10.0%, 12.5% and 17.5%, respectively, compared with the control. Accumulation coefficients ranged from 1.41 to 1.52 for Zn and from 0.9 to 1.17 for Cu. Hazard coefficients were substantially below 1.0: 0.162–0.182 for Zn and 0.05–0.098 for Cu, the lowest Cu hazard coefficient was recorded under the combined fertilization N60P60K90 – 0.05.
Conclusions. Mineral fertilization alters the intensity of Zn and Cu accumulation in onion, however, under the conditions of the experiment, the concentrations of both elements in the harvested product remained markedly below the MPC, and the risk indicators based on the hazard coefficient did not reach the threshold level. The combined fertilization N60P60K90 showed the lowest Cu hazard value, confirming that the elemental composition of onion can be managed by optimizing the plant nutrition system.