Simultaneous measurement of net nitrogen mineralization and denitrification rates in soil using nitrification inhibitor 3,5-dimethylpyrazole

A practical means to quantify the response of the rates of net N mineralization and denitrification over a wide range of soil water contents is generally lacking. This study examined the potential to use a nitrification inhibitor (NI) assay system to simultaneously estimate the rates of net N mineralization and denitrification, and applied the NI assay to assess the effect of water content on net N mineralization and denitrification rates in two soils with contrasting soil texture. The compound 3,5-dimethylpyrazole (DMP) applied at a rate of 200 mg kg−1 was found to provide essentially complete inhibition of nitrification over the duration of the soil incubation for two soils with contrasting soil texture (clay loam vs. sandy loam) and over a range of soil water contents (35%, 55%, and 85% water-filled pore space). This allowed net N mineralization to be estimated as the accumulation of soil ammonium (NH4+) and of denitrification as the disappearance of added nitrate (NO3-). Addition of DMP resulted in a small increase in soil respiration rate but did not appear to influence the rate of net soil N mineralization. The NI assay provides a practical means to quantify the rates of net N mineralization and denitrification simultaneously over a wide range of soil water contents. The assay can be readily scaled up to routinely test multiple soils in an efficient manner, has limited material costs, and is also relatively simple to perform.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author