Chemistry Reference
In-Depth Information
concentrations of certain mineral elements, or both.
15,16
Soils that are low in
phytoavailable minerals include:
10
N
alkaline and calcareous soils that have low availabilities of Fe, Zn and Cu;
these comprise 25-30% of all agricultural land;
17-19
d
n
1
r
2
n
g
|
1
N
coarse-textured,
calcareous
or
strongly
acidic
soils
that
have
low
Mg
content;
20
N
mid-continental regions that have low I content;
21,22
and
N
soils derived mostly from igneous rocks that have low Se content.
23,24
In contrast, excessive concentrations of potentially toxic mineral elements
may also compromise both crop production and human health.
25
On acid soils
occupying about 40% of the world's agricultural land, toxicities of Mn and
aluminium (Al) may limit crop production, while on sodic or saline soils (5-
15% of agricultural land) sodium (Na), B and Cl toxicities frequently reduce
crop production, and toxicities of Mn and Fe can occur in waterlogged or
flooded soils.
17,25
Excessive concentrations of Ni, Co, Cr and Se can limit
growth of plants on soils derived from specific geological formations (e.g.
serpentine)
17
and toxic concentrations of As, cadmium (Cd), Cu, mercury
(Hg), Pb and Zn have accumulated in agricultural soils in some areas due to
mining and industrial activities.
17
These toxic elements, contained in plants
and animals that graze on them, can accumulate in the food chain with
detrimental consequences for human health.
Soils also directly influence elements of accessibility and social preferences
for certain foods. An obvious European example is the importance of ''terroir''
in the perceived quality of certain wines and the social cachet attached to
them.
26
In a multi-factorial experiment, it was demonstrated that the effect of
soil appeared to be principally via effects on vine water status rather than
effects on mineral nutrition.
26
Similarly, in Asia, different rice types associated
with different soils and growing systems have assumed positions of political,
social and commercial importance.
27
d
n
6
h
3
2 Key Soil Constraints to Crop and Fodder Production
The concept of soil fertility is widely used as a framework for exploring the
relationships between crop productivity and soil characteristics. It is an
expression that synthesises chemical, physical and biological properties of soils
and their effects on the growth and activities of root systems and the shoot.
28
Soils can be inherently fertile because of combinations of high mineral nutrient
availability, good soil structure, high available water contents and appropriate
microbial and faunal communities that facilitate good root and shoot growth,
or be managed to promote soil fertility through, for example, cultivation
techniques that do not destroy structure or through additions of manures and
fertilisers.
29
More recently, crop genotypes have been developed to overcome
some key soil constraints to fertility.
