This paper reports the\ study of the total phosphorus determination in fertilizers by volumetric (phosphomolybdate) and by the differential spectrophotometric (Beckman, model B) method using the molybdovanadate reagent. This paper also presents the data obtained of the soluble phosphorus in 2% citric acid determined in fertilisers by the volumetric method and by the differential spectrophotometry and colorimetric (Klett-Summerson) methods. Ih was possible to conclude that the differential spectrophotometry and colorimetric methods presented a good precision and are faster than the volumetric method.