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

Nitric oxide (NO) compensation concentrations (mc), 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 (= mc) 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 mc. Both approaches resulted in similar values of mc. 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.