Manganese-Exchanged Smectite Clays as a Potential Controlled-Release Fertilizer for Mn Nutrition: Comparative...

To mitigate the negative effects of conventional fertilization, a novel concept of clay-based controlled-release manganese (Mn) fertilizers was investigated. Three Mn-exchanged smectites were synthesized via cation exchange: one montmorillonite (Mn(NO3)2) and two laponites (Mn(NO3)2 and MnCl2). Their composition, stability, and Mn-release behavior were assessed in saline medium across pH 5.5-8.2. A hydroponic experiment with barley (Hordeum vulgare cv. Antonia), a Mn-sensitive species, was conducted at pH 8.2 using sand amended with Mn-clays and compared with MnSO4 and MnEDTA. All treatments rapidly corrected Mn deficiency. At 8 weeks, biomass under Mn-laponite2, Mn-montmorillonite, and conventional fertilizers was comparable to or higher than that of the deficient control. Mn-laponites provided rapid Mn availability, whereas Mn-montmorillonite exhibited slower, sustained release. Smectite type thus controls Mn-release dynamics, supporting the use of synthetic clays as fertilizers in calcareous systems, though field validation is still pending.