Effect of dicyandiamide‐treated urea on furrow‐irrigated rice yield and nitrogen uptake

Abstract Furrow‐irrigated rice (FIR; Oryza sativa L.) has been grown in the upper Mid‐South since the 1980s. Nitrogen use in FIR is less efficient than direct‐seeded, delayed‐flood rice due to the lack of a flood, which ultimately protects applied nitrogen (N) from nitrification and subsequent denitrification. If urea applied to FIR fields could be protected from nitrification, N use efficiency could be increased. To address this issue, a test was initiated in 2018 to determine the utility of a blended‐urea product that included < 0.1% N ‐butyl‐thiophosphoric triamide (NBPT), a urease inhibitor that is recommended on most urea applications to rice, and 0.85% dicyandiamide (DCD), a nitrification inhibitor. A control with no supplemental N application plus six different N management programs were tested as urea + NBPT with or without DCD. Analyses across six sites over 2 years suggested that DCD did not affect any of the variables measured, including total N uptake, recovery efficiency of N, rice grain yield, and rice milling yield. While this is contrary to some previous studies, the product used in the current study contained approximately 10 times less DCD than previous studies in rice. Therefore, out of the products tested, the authors recommend purchasing the lowest cost option.