EFFECTS OF DCD ADDITION TO SLURRY ON NITRATE LEACHING IN SANDY SOILS

The effects of the addition of the nitrification inhibitor dicyandiami de (DCD) to cattle slurry, applied in autumn to an arable sandy soil, were investigated in a three-year field experiment. Treatments include d application of slurry with DCD in November and December, application of slurry without DCD in November, December and January, and an untre ated (slurry or DCD) control. Degradation of DCD, changes in mineral n itrogen in the soil, and leaching of nitrate and DCD were measured. De gradation of DCD in the topsoil was complete in May after application in the autumn before. However, at a depth of 90 cm, DCD was found thre e months after application. DCD remained present in leachate sampled a t this depth for more than one year after application. Most probably i t was then leached to the groundwater. Application of DCD considerably delayed nitrification. It had a large effect on the vertical distribu tion of mineral nitrogen in spring; more mineral nitrogen was found in the 0-40 cm soil layer and less in the 40-100 cm soil layer. However, neither time of application of the slurry nor addition of DCD had a s ignificant effect on nitrate leaching.