Relative Phytotoxicity of Dicyandiamide and Availability of its Nitrogen to Cotton, Corn, and Grain Sorghum

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Abstract
The nitrification inhibitor, dicyandiamide (cyanoguanidine) (DCD), can improve fertilizer N efficiency; however, yield reductions and phytotoxicity from the use of DCD have been reported. A greenhouse experiment was designed to determine the effect of DCD on growth, chlorophyll concentration and nutrient concentration of corn (Zea mays L.), cotton (Gossypium hirsutum L.), and grain sorghum [Sorghum bicolor (L.) Moench.]. Dicyandiamide‐N/urea‐N combinations of 0:60, 5:55, 10:50, 20:40, 30:30, 40:20, 50:10, and 60:0 mg kg−1 soil were applied to pots containing a Norfolk sandy loam (fine‐loamy, siliceous, thermic, Typic Paleudults) cropped to each of the three species. Increasing the proportion of N as DCD decreased plant dry weight and leaf chlorophyll concentration and increased stem‐leaf N concentrations. Nitrogen recovery decreased curvilin‐early from 103% to 4%, from 64% to −6%, and from 72% to 4% for corn, cotton, and sorghum, respectively, with increasing proportion of N as DCD‐N. The effects of DCD‐N on stem‐leaf tissue concentraitons of P, K, Ca, Mg, Fe, Mn, Zn, and Cu varied with DCD‐N concentration, plant species, and nutrient element. At lower DCD‐N concentrations, most nutrient element concentrations were affected by uptake of NH+4‐N derived from urea; while higher concentrations of DCD‐N resulted in increased nutrient element concentrations as a result of reduced plant growth.