Agriculture Reference
In-Depth Information
influences soil processes both as a gas and in solution; it controls soil pH in the mildly-
acid to mildly-alkaline range (Bruckert and Rouiller, 1979), is an important leaching
agent in solution as carbonic acid (Johnson
et al
., 1977) and influences the uptake of
plant nutrients. Carbon dioxide concentrations increase with depth in the profile and vary
seasonally (see,
e.g
., Buyanovsky and Wagner, 1983 and Amundson and Davidson,
1990); they are augmented at higher temperatures because of increased microbial
metabolism and are also higher when the soil surface is covered by snow.
At a broad scale, soil carbon dioxide concentrations during the growing season vary
with actual evapotranspiration (Figure I.14). Using this relationship, Brook and Box
(1983) predicted growing season carbon dioxide concentrations of less than 0.1 % in
deserts, 0.1-0.25 % in the conifer forests of North America and Eurasia, 0.6-1.6 % in
North American deciduous summer green forests and 0.6-4.0 % for rainforests, monsoon
and certain other tropical forests. Concentrations may thus be expected to be highest in
those moist tropical environments where few moisture limitations exist and lowest in dry
and semi-arid desert situations (Brook and Box, 1983). Vegetation change and other
disturbances generally reduce stocks of soil organic matter and lead to lower soil carbon
dioxide concentrations (Brook and Box, 1984).
1.2.3
ANAEROBIOSIS
In well-aerated soils, oxidative reactions dominate such processes as organic matter
decomposition, the conversion of ammonium salts to nitrite and nitrate, of reduced forms
