Evaluation of the acetylene inhibition method to measure denitrification in unsaturated zone

Abstract

A sound understanding of the transport and fate of farm nutrients (such as nitrogen and phosphorus) is a key component in our understanding and management of the likely impacts of these nutrients on fresh water quality and ecosystem health. Denitrification is an important nitrate attenuation process in soil-water systems that significantly influences the quality of groundwater and receiving surface waters. While denitrification in surface soils is widely studied, there is limited information available about its occurrence and distribution in the subsurface environment, especially below the root zone. One of the most common methods used to quantify denitrification is the acetylene inhibition (AI) method. On the other hand, subsurface denitrification studies using the AI method vary in methodological details, particularly in the determination of the denitrifying enzyme activity (DEA), which gives a snapshot of the potential of the soil to denitrify at the time of sampling. Luo et al. (1996) conducted a study to standardise DEA measurements for New Zealand soils, but it was carried out with samples from the surface soil layer (0-10 cm). Given the much lower biological activity in subsurface soils, this study aims to evaluate and determine the appropriate procedures for AI method to measure DEA in soil samples from the unsaturated zone.