THE EFFECT OF WATER-MOVEMENT ON THE TRANSPORT OF DICYANDIAMIDE, AMMONIUM AND UREA IN UNSATURATED SOILS

A laboratory experiment was conducted to investigate the relative mobility of dicyandiamide (DCD) and jointly applied ammoniacal salts or urea in three different soils of lower Egypt, and to determine the extent to which DCD separates from N‐fertilizer in unsaturated soil undergoing leaching. The experimental results suggest that, under conditions of water flow, DCD is readily separated from NH4+ but parts from urea to a far lesser extent. The large difference in mobility between DCD and NH4+ should severely limit the effectiveness of DCD as a nitrification inhibitor in the three soils considered when applied in conjunction with ammoniacal salts. In two out of three cases, the situation is similarly unfavorable in the case of joint DCD and urea application. However, the observation that DCD, in a low CEC sandy loam, moves within the soil solution at a slightly lower rate than urea suggests that joint application with urea would keep at least part of the DCD in contact with the NH4+ ions and, therefore, would preserve some of the effectiveness of DCD under leaching conditions in this soil. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim