Agriculture Reference
In-Depth Information
Humid
climate
Arid
climate
Intermediate
temperatures
Extremes of
temperature
(17-27
°
C)
Soil pH
5-8
High or low
soil pH
Deciduous forest
rain forest
Coniferous
forest, heathland
Permanent
grassland
Continuous
cultivation
Return of crop
residues, manuring
Excess fertilizer
Dynamics of soil biomass
changes (White 1997).
Reproduced with
permission of Blackwell
Science Ltd.
Figure 2.18
and pesticides
Good drainage,
aeration
Poor drainage,
waterlogging
ganisms and its decomposition rate is accelerated. Higher surface soil tempera-
tures are also attained when the vegetative cover and protective litter layer are re-
moved.
Activity of the Soil Biomass
The size and species diversity of the soil microbial population respond to envi-
ronmental factors and soil properties, as described in preceding sections. Soil an-
imals are also affected by types of litter, temperature variations, moisture, pH, and
management practices, such as cultivation and the use of agricultural chemicals.
Environmental factors and soil management also influence the physiological
activity of soil organisms. Striking effects occur, for example, when the soil is par-
tially sterilized with toxic chemicals, such as ethylene dibromide. When favorable
conditions are restored, rapid multiplication of the surviving organisms, feeding
on the bodies of killed organisms, produces a flush of decomposition and a surge
in the production of CO
2
. Similar flushes of decomposition occur in soils sub-
jected to air-drying followed by rewetting and in soils of cold temperate regions
when they pass from a frozen to thawed state.
The dynamics of changes in soil biomass in response to variations in soil and
environmental factors are summarized graphically in figure 2.18.
2.3.5.3
Summary Points
2.4
The main points presented in this chapter on mineral and organic matter in soil
follow.
■
The solid phase of soil, comprising ca. 50% by volume, consists of minerals and
organic matter. The particle size distribution of the mineral matter is measured
