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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. (C) 1998 Elsevier Science Ltd. All rights reserved.