Synthesis of potassium/ammonium phosphates and alumina composites through a mechanochemical approach is presented for the first time. gamma-alumina and the phosphate are coground and the ground products are characterized by X-ray diffraction and infrared spectroscopy. Quantitative evaluation of the remaining soluble part of the prepared amorphous phase at a low percentage around 10% demonstrates a potential use of the ground samples as slow-release fertilizers.