Study On Permeability Of NPK Nutrients Through Polymer Membrane From Aqueous Solution Of Compound Fertilizer

With the polymer-coated slow/controlled release fertilizer, the addition effects of P or K fertilizer into the urea-water solution on the urea permeation characteristics through the polystyrene membrane that was previously prepared with the solution cast method were investigated by measuring the urea permeability from the solutions of urea-water, urea-NaH2PO4-water, urea-KCl-water, urea-NaCl-water, and urea-CaH2PO4-water at nominal temperature of 298 K using the Ussing chamber method. It was found out that the effects of P or K fertilizer addition on N permeability were substantial, which could be promotion or suppressing depending on the addition amount.At the same time, the permeability of N, P, K fertilizer nutrients through the PS membrane from the solutions of KH2PO4-water and urea-KH2PO4-water at nominal temperature of 298 K using the same experiment method was measured. It was found out that the N, P, K permeability were increase with the concentration of fertilizer for most of the solutions investigated. According to the "solution-diffusion" model, there existed two competing effects for the nutrient permeability. With the increase of the fertilizer nutrient concentration, the solubility of nutrient in the polymer membrane was increased and the diffusion coefficient in the polymer membrane was decreased due to formation of associated complexes resulted from molecule-molecule and molecule-ion interactions in the aqueous compound fertilizer solutions. At low fertilizer nutrient concentration, the increase of solubility of nutrients in the polymer membrane played a more important role on the nutrient permeability; while at high nutrient concentration, the decrease in the diffusion coefficient dominated.