Combined application of nano-magnesium oxide and humic acid improves potato drought tolerance and soil health

BACKGROUND: Drought is a major threat to crop production. Although different biostimulants and nano-fertilizers have shown potential to mitigate drought stress, their combined effects remain poorly understood. METHODS: This study investigated the effects of soil-applied humic acid (HA) and foliar nano-magnesium oxide (Nano-MgO) to alleviate drought stress in potato (Solanum tuberosum L.). A pot experiment was conducted under two irrigation regimes, well-watered conditions maintained at 80% field capacity (FC) and drought stress conditions maintained at 40% FC; two HA levels (0 and 2000 mg kg⁻¹ soil); and four foliar Nano-MgO concentrations (0, 20, 40, and 60 mg L⁻¹). RESULTS: The results demonstrated that drought stress significantly reduced plant height, stem diameter, biomass, chlorophyll content, and tuber starch and protein content while increasing oxidative stress markers like malondialdehyde (MDA). The combined application of HA and Nano-MgO (60 mg L⁻¹) significantly counteracted these detrimental effects. This treatment enhanced chlorophyll retention, increased antioxidant enzyme activities, reduced oxidative damage, and improved osmotic regulation. As a result, tuber yield, starch, and soluble sugar content under drought were significantly improved compared to untreated drought-stressed plants, although values remained below well-watered plants. Soil enzyme activities were also significantly improved, indicating enhanced soil health. The improved plant performance is attributed to HA amendment and efficient foliar Mg delivery by Nano-MgO, which together strengthen photosynthesis and antioxidant defense. CONCLUSIONS: The combined use of humic acid and Nano-MgO is a sustainable and highly effective approach to enhance drought resilience in potato.