Effect of urea pellet size and dicyandiamide on residual ammonium in field microplots

Abstract

Abstract Nitrification of urea can be slowed by adding a nitrification inhibitor or by fertilizer localization. The purpose of this research was to compare the effects of urea pellet size (0.01, 0.1, and 1.0 g) and level of dicyandiamide (DCD) addition (0, 1, 2, 5, and 10% of N as DCD‐N) on residual ammonium in field microplots. Trials were conducted at ten locations in North Dakota during 1988 and 1989. Adding DCD to 0.01 g urea pellets slowed nitrification at all locations and the lower rates of DCD (1–2% of N as DCD‐N) often performed as well as higher rates. Increasing urea pellet size to 1.0 g was more effective in inhibiting nitrification than adding DCD to 0.01 g pellets. Increased pellet size plus addition of DCD led to a very slow nitrification. A 1.0 g urea pellet containing 1–2% of N as DCD‐N should be a practical fertilizer formulation where a very slow nitrification is required.