Ornamental lawns and sports turfs are a major field of application for slow release fertilizers. With a lower burning potential compared to soluble forms, the required amount of fertilizer can be applied with a reduced number of applications providing a longer lasting release of nutrients while minimising their loss by leaching (Carrow et al., 2001). The products of polymerization of urea (urea formaldehyde and methylene urea) have been used for decades as slow release nitrogen fertilizers (Christians, 2004). The release of mineral nitrogen available for plants from these insoluble sources depends on the breakdown of the polymeric molecules with the eventual release of ammonium in the soil. The process, referred to as “mineralization”, occurs naturally in soil and it is the result of the soil microbial activity. As such it is greatly affected by soil type (Stanford and Smith, 1972) and environmental conditions such as soil moisture content and temperature (Cassmann and Munns, 1980). In order to consider the effects of soil type and actual microbial activity on the release rate of mineral nitrogen from polymeric slow release fertilizers, incubation methods have been developed (Koivunen and Horwath, 2004). The aim of the research was to determine the release of plant available nitrogen from different polymeric sources by a laboratory incubation method where the conditions occurring in a newly constructed sand-based growing medium are reproduced