The aim of the paper was to determine changes in the content of total phosphorus and its selected forms in soil under maize treated with mineral fertilization. The activity of enzymes participating in transformations of this bioelement was also investigated. In October 2008, soil was sampled from a field experiment set up at the Agricultural Experimental Station in Grabów nad Wisłą, conducted by the IUNG Institute in Puławy. The experiment involved the application of nitrogen in the form of ammonium nitrate at rates of 0, 50, 100, 150, 200 and 250 kg N ha–1 and concomitant P, K, Mg, Ca and S fertilization. The following determinations were made on the soil samples: the content of total phosphorus, phosphorus in organic compounds and available phosphorus as well as the activity of alkaline and acid phosphatases. The analysis of variance showed a significant effect of the experimental factors on changes in the content of total phosphorus and its selected forms. The content of available phosphorus was 55.85 mg PE-R kg–1, which classified the soil to class III, that is with a moderate content of this nutrient. The lack of phosphorus fertilization (KMgCaS variant) as well as the use of high nitrogen rates changed the soil phosphorus abundance class from average to low. The soil content of phosphorus in organic compounds was about 25% of the total phosphorus content, but when nitrogen fertilization had been applied at the rates above 100 kg N ha–1, Porg decreased to about 15%. The activity of phosphomonoesterases was the highest in soil from the treatments not fertilized with phosphorus (KMgCaS). A close dependence was found between the activity of acid phosphatase and the total phosphorus content or the content of its examined forms. The value of the coefficient of correlation between the AcP activity and the PE-R content in soil was r=-0.83, p

18.3.2013