Foliar fertilization with zinc in reproductive stages of soybean cultivars for grain biofortification

ABSTRACT The goal was to assess the impact of foliar fertilization with zinc (Zn) at different phenological stages of plants on the biofortification of soybean cultivar grains. The experimental design was a split-plot factorial design over time. Eight soybean cultivars (BMX Foco IPRO, BMX Desafio RR, BMX Bônus IPRO, DM 68i69 IPRO, NEO 680 IPRO, DM 80i79 IPRO, BMX Única IPRO and NEO 710 IPRO), and three moments of Zn application via foliar (first: application of 2 kg ha–1 of Zn at sowing; second: application of 2 kg ha–1 of Zn at sowing and 1.0 kg ha–1 in R3; third: application of 2 kg ha–1 of Zn at sowing and 0.5 kg ha–1 in R3 and 0.5 kg ha–1 in R5) evaluated in the 2021-2022 and 2022-2023 harvests. The following was evaluated: chlorophyll indexes; plant height; leaf Zn content (LZn); number of pods; weight of one hundred grains; productivity (PROD), and Zn content in grains (ZnG). The responses varied depending on the cultivars, with the BMX Bônus IPRO and BMX Única IPRO being the most responsive to foliar application of Zn, especially during the R3 and R3 + R5 stages. Yield and ZnG were higher when the foliar application of Zn was divided between the R3 and R5 stages. Application of Zn at R3 and R5 proved to be an effective strategy for biofortification of soybeans, significantly increasing ZnG (exceeding 1 mg kg–1) and productivity (surpassing 316 kg ha–1).