Micronutrient Seed Coatings of Layered Double Hydroxides Overcome Seedling Toxicity and Improve Micronutrient Uptake in Comparison with Soluble Micronutrient Coatings

Zinc (Zn), boron (B), and molybdenum (Mo) are micronutrients, essential to crops, which can be efficiently applied to crops via seed coatings. However, fast micronutrient release from soluble seed coatings brings seedling toxicity risks. Hence, this study developed novel Zn-B-Mo slow-release seed coating compounds, i.e., nanostructured Zn₂Al or Zn₃Al-layered double hydroxides (LDHs) loaded with (poly)borate and molybdate. Assessment of the micronutrient release properties showed that both LDH compounds gradually dissolved at a pH of ∼ 4.5, releasing Zn, B, and Mo, while Zn₃Al-B-Mo released Mo more slowly than Zn₂Al-B-Mo through anion exchange (pH ∼ 7). Finally, in a seedling establishment trial with coated chickpea seeds, at elevated micronutrient doses, the Zn₃Al-B-Mo LDH coating prevented adverse effects on seed emergence and seedling yield that were observed with a corresponding soluble coating due to seedling toxicity. Taken together, micronutrient LDHs prove to be promising compounds for controlling micronutrient supply from seed coatings.