Dynamics of Mineral Nitrogen in Soils Treated with Slow‐Release Fertilizers

Abstract

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 (NO₃ ⁻) and ammonium (NH₄ ⁺) 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 NO₃ ⁻ 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.

Keywords:

• Slow‐release fertilizers
• nitrification inhibitor
• mineral nitrogen
• “priming effect”

Acknowledgments

This research has been funded by the “Ispettorato Centrale delle Repressioni Frodi” of the Italian Board of Agricultural and Forestry Policy, and by the Alma Mater Studiorum University of Bologna (ex quota 60%). We thank Andrea Simoni for the technical support.