In this study, five different slow-release fertilizers were incubated in two soils, and their nitrogen (N) dynamics was followed for 4 months. Four of the fertilizers used were organic: two were hydrolyzed fur, one was made by hydrolyzed fur, farmyard manure, horn, and hoofs (Endurance), and one contained synthetic organic N [isobutylidendiurea (IBDU)]. The fifth, on the contrary, was a mineral fertilizer (Entec 26) containing both nitrate (NO 3 2 ) and ammonium (NH 4 þ ) and a nitrification inhibitor (3,4 DMPP). The two soils used were a sandy loam (SL) and a clay loam (CL). The fertilizer-N release was conditioned by both the fertilizers and the soil characteristics. The highest accumulation of mineral N as NO 3 2 was observed in the SL soil for all the treatments. The lowest net N release was observed in both soils with End, which was found to be the most resistant to microbial attack and degradation. The two fur-based fertilizers released similar amounts of N, which was higher in the SL soil than in the CL soil. The highest accumulation of fertilizer-derived N in the CL soil resulted from IBDU; however, the net accumulation of N in the SL soil with this fertilizer was even higher than the amount of N initially added. This fact was attributed to an increase in mineralization of the soil's native organic N. A real positive "priming effect" was also observed in the SL soil with E26. On the contrary, E26 caused a low level of N accumulation in the CL soil.

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