EFFECT OF MIXING VARYING QUANTITIES OF DICYANDIAMIDE WITH AMMONIUM FERTILIZERS ON NITRIFICATION OF AMMONIA IN SOILS

Abstract

A series of laboratory experiments were conducted to evaluate the effect of dicyandiamide on the transformation of fertilizer nitrogen in Georgia soils. These studies indicated that dicyandiamide inhibited nitrification of ammonium sulphate at all rates utilized. The inhibitory action of dicyandiamide was attributed to its toxic effect on the nitrifying organisms which failed to function in the presence of dicyandiamide. Complete nitrification eventually occurred but only after a long period.Decomposition of dicyandiamide was more rapid in fine-textured Cecil sandy loam containing relatively more organic matter than on the coarse-textured and low organic matter Lakeland sandy soil. Soil texture and organic matter content are two factors that must be considered in evaluating the length of time that dicyandiamide will inhibit nitrification in any given soil.Sucrose apparently provided a quickly available source of energy for soil microorganisms that utilized the dicyandiamide as a source of nitrogen and preventing its inhibiting effect on nitrification. The nitrogen from the dicyandiamide was eventually mineralized as indicated by the higher total ammonium and nitrate nitrogen found at the end of incubation period.