Evaluation of phosphate in fertilizers by means of the alkaline ammonium citrate extraction according to Petermann.

  • R. Boxma


The phosphate extraction with alkaline ammonium citrate solution for the control of phosphate in fertilizers was subjected to a critical examination. The contribution of inferior phosphate forms such as tricalcium phosphates and apatites to the available P2O5 percentage can be excluded to a great extent by using a narrow sample solvent ratio. However, the dissolution rate of dicalcium phosphate in alkaline ammonium citrate solution limits the narrowing of the ratio. The dissolution rate of dicalcium phosphate can be increased, if instead of intermittent manual shaking, mechanical shaking is applied. Extraction of 1.0 g sample with 200 ml of alkaline ammonium citrate solution at 65 deg C under mechanical shaking for 1.5 hours is preferred to other methods for quality control of phosphate in fertilizers. The extraction method with neutral ammonium citrate solution is not reliable, because this method makes little or no distinction between high quality and low quality fertilizers. (Abstract retrieved from CAB Abstracts by CABI’s permission)