NITROUS-OXIDE PRODUCTION AND DENITRIFICATION IN SCOTTISH ARABLE SOILS

Nitrous oxide (N2O) emissions and concentrations in the soil atmosphere were measured at a number of sites of differing soil type in south-east Scotland between 1985 and 1988. Concentrations followed log-normal distributions and were significantly affected by soil type, tillage treatment, and nitrate application rate. The shape of the profiles suggested significant consumption in the upper 5 cm, making calculations of emission rates using Fick's Law unsatisfactory. Emission rates measured using closed flux chambers were at least one order of magnitude smaller from heavier-textured arable soils than from lighter ones. Denitrification fluxes measured by field application of the acetylene inhibition technique were lowest in a clay loam, and highest in an alluvial sandy loam; this was attributed to a failure to achieve a satisfactory distribution of acetylene in the heavier soil. Denitrification rates in soil cores generally exceeded measured surface fluxes; incubation at decreased oxygen concentrations typical of those measured in the field produced a further significant increase. Core incubation should be used as an alternative to in situ field measurement only if the oxygen concentration in the incubation vessels is adjusted to mimic that in the field; otherwise denitrification rates may be significantly underestimated.