EFFECT OF THE NEW NITRIFICATION INHIBITOR DMPP IN COMPARISON TO DCD ON NITROUS OXIDE (N2O) EMISSIONS AND METHANE (CH4) OXIDATION DURING 3 YEARS OF REPEATED APPLICATIONS IN FIELD EXPERIMENTS

In a 3-year field experiment the effect of the new nitrification inhibitor DMPP (3,4-dimethyl pyrazole phosphate, trade name ENTEC) on the release of N2O and on methane oxidation was examined in comparison to dicyandiamide (DCD). Soil samples were analysed for the concentrations of ammonium, nitrite, nitrate and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N2O by 41% (1997), 47% (1998) and 53% (1999) (with an average of 49%) while DCD reduced N2O emissions by 30% (1997), 22% (1998) and 29% (1999) (with an average of 26%), respectively. Both nitrification inhibitors (NI) failed to affect methane oxidation negatively. The plots that received DCD or DMPP, respectively, even seem to function as enhanced sinks for atmospheric methane. DMPP apparently stimulated methane oxidation by ca. 28% in comparison to the control. The concentrations of ammonium remained unaffected by nitrification inhibitors whereas the amounts of nitrite diminished in the plots treated with DCD by 25% and with DMPP by 20%, respectively. Nitrate concentrations in soil were in both NI treatments 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. Dicyandiamide was mineralized more rapidly than DMPP (data for the cropping season in 1997 as an example).