Influence of soil parameters on the effect of 3,4-dimethylpyrazole-phosphate as a nitrification inhibitor

Nitrification inhibitors specifically retard the oxidation of NH4+ to NO2- during the nitrification process in soil. In this study I the influence of soil properties on the nitrification-inhibiting effect of 3,4-dimethylpyraz ole-phosphate (DMPP), a newly developed nitrification inhibitor, has been i nvestigated. Based on short-term incubation experiments. where the degradat ion of DMPP could be largely disregarded, the oxidation of the applied NH4 was more inhibited in sandy soils compared with loamy soils. The influence of soil parameters on the relative NO2- formation could be described by a multiple regression model including the sand fraction, soil H+ concentratio n and soil catalase activity (R-2=0.62). Adsorption studies showed that the binding behaviour of DMPP was influenced markedly by soil textural propert ies, viz. the clay fraction (r(2)=0.61). The adsorption of DMPP was found t o be an important factor for the inhibitory effect on NH4+ oxidation in a s hort-term incubation (r(2)=0.57). It is concluded that the evaluated soil p roperties can be used to predict the short-term inhibitory effect of DMPP i n different soils. The significance of these results for long-term experime nts under laboratory and field conditions needs further investigation.