Preparation of single-material carrier formulation fertilizer made by material extrusion three-dimensional printing and its controlled release effect

As a processing technology that can rapidly fabricate customized products in small batches, three-dimensional (3D) printing has great application potential in horticultural gardens. On the basis of existing studies on controlled releasing materials for 3D printing, the carrier materials for solo nutrition were developed after a range of formulation screening. The new formulations were suitable for material extrusion 3D printing and the single-material carrier formulation fertilizer contained sodium alginate or xanthan gum as a binder, mannitol as a filler, ethanol/water with fixed ratio as a solvent, sepiolite as a thickening agent, and urea as the core fertilizer. It was confirmed that the maximum adding ratio of urea could reach 1∶4 [m (urea)∶V (solvent)] when using sodium alginate as a binder, while the maximum adding ratio could reach 3∶4 [m (urea)∶V (solvent)] when using xanthan gum as a binder. It was confirmed that the developed formulation could also be used as the carrier of other types of nutrients including KCl, K₂HPO₄, and ZnSO₄. This work also demonstrated that it was possible to combine different nutrients and achieve element couplings by using multi-material extrusion 3D printing technology. Through the printing parameter adjustment experiment, the optimal printing was achieved when the printing speed was 200 mm/min, and the extrusion speed was 0.02 mm/s, and the extrusion height was 1 mm, and the nozzle diameter was 1 mm. The controlled release period of different formulations were further studied by the sand column leaching method. There were significant differences between the controlled release period of single-material carrier formulation fertilizers under different formulations and their post-treatments. The modified formulation with sepiolite can obviously change the release rate of single-material carrier formula fertilizer and the longest controlled release period reached 30 d.