Transfer and water-retention properties of seed-pelleting materials

Until now, the choice of materials for seed pelleting has been mostly empirical. We have analysed coating materials (silicate powder A, clay B and hydrophobic clay C) and their water-transfer properties. Seed-pelleting materials were studied with conventional soil-analysis techniques. An original device for studying water transfer through a thin layer of powder was designed to simulate the transfer of water from the soil to the seed, through the pelleting material. Different parameters were studied: particle-size distribution, water-retention curve of materials, thickness of powder, influence of concentration of adhesive in pelleting, etc. The sintered glass on which the powders were placed in the device constituted a limiting factor. The major component, a silicate powder (A), consisting of large particles, is responsible for the general structure of the pelleting. Introduction of clay (B) gave intermediate properties between A and C to water-transfer capacity. Hydrophobic clay (C) can be used to control the incoming flow. The particle-size distribution and wettability of materials have a direct impact on the transfer capacity of the powder. High adhesive concentration had a negative effect on water transfer. These parameters and the formulation have a direct impact on imbibition of pelleting materials. Objective tools, like the analytical methods used in this study, enable water-transfer parameters and consequences on imbibition of coated seed to be understood.