Controlled release studies of boron and zinc from layered double hydroxides as the micronutrient hosts for agricultural application

Two forms of zinc-aluminium layered double hydroxides (ZnAl-LDH) with borate association (iZA and cZA) were prepared by ion-exchange process and in-situ co-precipitation. The received materials were examined using several characterization techniques, e.g. x-ray diffraction (XRD), scanning- and transmission-electron microscopy (SEM and TEM). The XRD diffractograms suggested that only monoborate ions (possibly trigonal and tetrahedral forms) were involved in the intercalation and adsorption. Elemental analyses, i.e. inductive coupled plasma-optical emission and atomic absorption spectroscopies, were used to determine the starting zinc and boron compositions, and the contents after the dissolution experiment in water, soil, and plant growth study. The iZA and cZA samples were found to controlled-release Zn and B contents which can be used as micronutrient sources in agricultural application. The releases of the two nutrients are suggested to initiate from the anionic exchange of BO3(3-) and the transformation of Zn2+ from LDH basal plane. The plant experiments treated with these iZA and cZA exhibit improvements in plant growth, evidently attributed to the controlled and sustainable releases of boron and zinc for assisting macronutrient uptakes when used with the NPK fertilizer.