Simultaneous measurement of nitric oxide production and consumption in soil using a simple static incubation system, and the effect of soil water content on the contribution of nitrification

Abstract

Nitric oxide (NO) compensation concentrations ( m c), NO uptake rate constants ( k) and NO production rates ( P) were determined in four different soils at three different soil moisture contents using serum bottles as a static incubation system. Two different approaches were compared. In the first approach the release of NO was measured until a constant NO concentration (= m c) was reached indicating that the NO production rate equalled the NO consumption rate so that the net NO release became zero. In a second approach NO was added to the bottles and the consumption of NO was measured until the compensation concentration was reached. In both cases, k was determined by curve fitting and P was calculated as the product of k times m c. Both approaches resulted in similar values of m c. However, values of k and P were often different. If the soils produced only small amounts of NO, the increase of NO was usually too small to allow a reliable curve fitting for calculation of k and P. Thus, the determination of k and P was more reliable when using the NO consumption approach. Nitrification was specifically inhibited in the presence of 10 Pa acetylene. The inhibition experiments showed that nitrification was the main NO-producing process in all soils except in an acidic forest soil. Increase of soil moisture contents from 30 to 60% maximum water-holding capacity resulted in a decrease of the contribution of nitrification to NO production.