Nitrogen release from hydroxyapatite compounds as potential foliar fertilizers

Abstract

This thesis studies the nitrogen release from a Hydroxyapatite (Hap) compound loaded with urea. The aim is to determine how the presence of ureases may affect the rate of release at two different temperatures. For comparison, a Hap compound loaded with NH4+ is subjected to the same factors. Kinetic studies were performed, and N concentration was fitted to selected mathematical models. A modified Langmuir model was selected as the most representative of the kinetic models studied. It allowed a better analysis of the results. It was concluded that the higher temperature promotes urea release from the Hap compound and, in the presence of ureases, the transformation of urea into ammonium.