Lysimeter experiments on the translocation of the carbon-14-labelled nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in a gleyic cambisol

The environmental behaviour of the nitrification inhibitor. 3,4-dimethylpyrazole [pyrazole-5-C-14]phosphate [C-14]DMPP, was investigated in two lysimeters ( LI m depth, I m(2) surface area) containing undisturbed monoliths of a gleyic cambisol soil. [C-14]DMPP was applied in May 1996 to potatoes (cv. Nicola) at a rate of 847.5 g ha(-1) together with 120 kg N ha(-1) in the form of ammonium sulphate nitrate. The succeeding rotational crop of winter wheat (cv. Tilburi) received a split application at a rate of 1,133 g ha(-1) [C-14]DMPP together with 160 kg N ha(-1) in 1996/1997. No DMPP was applied to the following crop of winter barley (cv. Loreley). During the first year of the experiment, about 44.8% of the annual precipitation of 915.5 mm was collected as leachate, in the second year, 36.4% (816.0 mm) and in the third year 55.3%. (935.0 mm). These leachates contained a total of 1.0% (first year), 1.1% (second year) and 0.5% (third year) of the applied radioactivity. DMPP was not detected above 0.1 mug l(-1) (drinking water limit) in any of the leachate samples examined. Residue-equivalent radioactivity amounted to a maximum of 3.4 mug l(-1), 12.3 mug l(-1), and 2.6 mug l(-1), respectively, during the first, second and third year of the experiment. At the time of the potato harvest. 42% of the applied radioactivity was recovered in the topsoil (0-30 cm), and 41% in the 0- to 20-cm layer. Fifty-one percent and 38% of the applied radioactivity were found in the topsoil after the wheat and barley harvests. respectively. A total of 0.39% of the applied radioactivity was found in the potatoes. 0.51% in wheat, predominantly in the straw (0.43%), and 0.03% in barley.