Abstract
The effect of a heavy application (550 tonnes/ha) of unamended cow slurry to grassland in early spring (March) on the composition of the soil atmosphere was examined by analysing the gaseous phase under adjacent treated and untreated areas for a 12‐month period. Restricted aeration and products of intense reducing activity were observed in the slurry layer for 3 weeks, and in the underlying surface soil for several months, after the application; oxygen contents of the atmosphere to a depth of 80 cm were decreased and carbon dioxide contents increased, for 12 months. Although the slurry and soil never became completely anaerobic (minimum oxygen contents observed were 8% (v/v) in the slurry and 3.5% in the soil), high methane concentrations (6% in the slurry and 1.7% in the soil) indicated that a large proportion of the slurry and surface soil volumes were occupied by anaerobic volumes shortly after the application. Other hydrocarbon gases (ethane, ethylene, propane) were evolved, but did not accumulate to concentrations greater than 7 parts/10^6^.
Nitrous oxide evolution indicated a pattern of gaseous N loss from the soil and slurry, presumably due to denitrification. Major evolution occurred in the slurry in May, June and July, and in the surface soil at the 10‐cm depth in July–August. Nitrous oxide was detected continuously in the winter, and in concentrations as high as 680 parts/10^6^, at a depth of 40 cm below the soil surface of the treated grassland after nitrate had been leached to this depth by autumn and winter rains. Nitrous oxide was detected continuously at 80 cm below the soil surface in spring and early summer, and again in the following winter, under treated as well as untreated areas.
The observed consequences of the slurry application are attributed to physical effects in restricting aeration, in association with the effect of the organic substrates on soil respiratory activity.