EDTA Shuttle Effect vs. Lignosulfonate Direct Effect Providing Zn to Navy Bean Plants (Phaseolus vulgaris L 'Negro Polo') in a Calcareous Soil

Zn-Lignosulfonates (LS) fertilizers are used as an eco-friendly alternative to chelate formulations. The mechanisms of Zn release in the rhizosphere by both types of products are compared. The ability to provide Zn to Phaseolus vulgaris L of non-modified and chemically modified ZnLS and ZnEDTA is compared in a hydroponic assay. Stable isotope ⁶⁷Zn was used to study Zn source (fertilizer, Zn_Fer, or native, Zn_Nat) uptake and distribution in plants in two soil pot experiments. ZnEDTA was the best treatment to provide both Zn_Fer and Zn_Nat to navy bean plants. A shuttle effect mechanism and an isotopic exchange may occur. ZnLS from eucalyptus (ZnLSE) provides more Zn to the plant than LS from spruce. Chemical modifications of ZnLSE does not improve its efficiency. A double dose of ZnLSE provides similar Zn_Fer in leaves and similar soluble Zn_Fer content in soil than ZnEDTA. A model for the Zn fertilizers behavior in the soil and plant system is presented, showing the shuttle effect for the synthetic chelate and the direct delivery in the rhizosphere for the ZnLS complex.