Chemistry Reference
In-Depth Information
d
n
1
r
2
n
g
|
1
d
n
6
h
3
Figure 2
Figurative summary of components of soil fertility. (Source: adapted from
Stockdale).
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In essence, the task of farmers and their advisers is to identify the soil
constraints to crop production, and then to ameliorate these with inputs and/
or management practices that minimise them so that the potential yield
determined by genetic and climatic properties can be approached (Figure 2).
The main factors limiting yields on many soils are: depth of soil, soil
compaction, water supply, nutrient supply, erosivity, and soil reaction,
including pH and salinity. These key soil constraints vary between soils and
their past histories of use and management. For example, salinity is often a
constraint to production on soils irrigated with low quality water and with no
or
limited
drainage,
whereas
human-induced
compaction
may
constrain
production on soils cultivated with heavy machinery.
2.1 Soil pH
Many aspects of soil chemistry, and hence soil fertility, are influenced by soil pH,
including the bioavailability of plant mineral nutrients, microbial activity and root
growth.
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Nearly all natural soils have a pH between 4 and 10. Soil pH at a given
location is a function of soil composition (the relative proportions and types of
organic and mineral constituents) and the consequent ion-exchange and
hydrolysis reactions. Generally, soil pH values of ,4 are uncommon because in
such acid soils aluminosilicate and oxide minerals dissolve and buffer the pH.
