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-dimethylpyrazole-phosphate (DMPP), a newly developed nitrification inhibitor, has been investigated. Based on short-term incubation experiments. where the degradation 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+ concentration and soil catalase activity (R-2=0.62). Adsorption studies showed that the binding behaviour of DMPP was influenced markedly by soil textural properties, viz. the clay fraction (r(2)=0.61). The adsorption of DMPP was found to be an important factor for the inhibitory effect on NH4+ oxidation in a short-term incubation (r(2)=0.57). It is concluded that the evaluated soil properties can be used to predict the short-term inhibitory effect of DMPP in different soils. The significance of these results for long-term experiments under laboratory and field conditions needs further investigation.