Objectives Rainfall leads to a high loss rate of traditional zinc fertilizers sprayed on the leaf surface, greatly reducing the effectiveness of zinc fertilizers. Based on the characteristics of nanomaterials, such as small size, surface and interface effects, and strong adsorption effects, exploring the efficacy and mechanisms of foliar application of nano zinc fertilizers under rainfall conditions has significant application value.

Methods The experiment was setup with 5 treatments: CT₁, complete nutrient solution treatment; CT₂, control reatment, spraying 0.1% Tween; CT₃, spraying ZnSO₄·7H₂O; CT₄, spraying EDTA-Zn; CT₅, spraying Nano-Zn. Adopting the method of indoor hydroponic experiments to compare the zinc nutritional effects of foliar application of nano zinc fertilizer (ZnO-NPs) with traditional zinc fertilizers (ionic zinc fertilizer ZnSO₄·7H₂O and chelated zinc fertilizer EDTA-Zn) on peanut leaves under simulated rainfall conditions. By measuring the effects of three types of zinc fertilizer treatments on peanut plant growth, biomass, net photosynthetic rate, antioxidant enzyme activity, as well as zinc content and distribution in leaves, the physiological mechanisms causing these differences in effects were explored.

Results Under non-rainfall conditions, foliar application of traditional zinc fertilizer was more effective for peanuts than nano zinc fertilizer. However, under rainfall conditions, foliar application of nano zinc fertilizer effectively promoted the growth of peanuts. The plant height of peanuts was significantly increased by 16.80%, 9.68%, and 12.85% compared to the blank control group CT₂ and traditional zinc fertilizers CT₃, CT₄, respectively. The above-ground biomass and leaf zinc content reached 2.48 g/plant and 0.078 mg/plant, respectively, which were increased by 75.05% and 466% compared to the blank group, 20.97% and 19.54% compared to ionic zinc fertilizer, and 24.37% and 9.22% compared to chelated zinc fertilizer. Moreover, compared to non-rainfall conditions, leaf zinc content of peanuts under rainfall conditions was increased by 77.36%, antioxidant enzyme activity was slightly increased, and malondialdehyde content was slightly decreased. In contrast, ionic zinc fertilizer ZnSO₄·7H₂O and chelated zinc fertilizer EDTA-Zn reduced aboveground biomass by 8.17% and 23.70%, and decreased leaf zinc content by 25.53% and 34.28% under rainfall conditions, with a greater decrease in photosynthetic efficiency compared to nano zinc fertilizer. Analysis using synchrotron X-ray fluorescence microscopy (XFM) showed that the signal intensity in leaves treated with nano zinc fertilizer under rainfall conditions was significantly higher than that in other zinc fertilizer treatments. In terms of rain resistance, the leaching amount of nano zinc fertilizer is only 0.01 mg/plant, which was 45%−50% of that of traditional zinc fertilizer, while the zinc content adhered to the leaves was 0.02 mg/plant, 4−5 times that of traditional zinc fertilizer. This depended on the contact area and surface tension between the fertilizer and the leaves. Contact angle measurements of the three zinc fertilizers showed that the contact angle of nano zinc fertilizer was smaller than that of traditional zinc fertilizers, with a greater surface tension, and its adhesion work (27.95 mN/m) was increased by 37.48% and 28.98% compared with traditional zinc fertilizers CT₃’s 20.33 mN/m and CT₄’s 21.67 mN/m, respectively.

Conclusions Foliar application of nano zinc fertilizer can effectively enhance the adhesion between fertilizer and leaves during the rainy season and other extreme weather conditions, thereby reducing leaching losses, promoting the absorption of zinc by plant leaves, and significantly increasing the zinc nutrition levels in peanuts.