Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

particularly if the land has been over-grazed by
livestock. Under semi-arid conditions wind
erosion and desertification are serious problems.
A fertile soil supporting a swiftly growing crop
is much less erosion prone than a poor soil
supporting a poor crop. The better developed the
surface canopy the greater the protection against
wind and water action. Because of their vigorous
root systems and large residues, high yielding
crops help to anchor the soil. The roots and
residues returned to the soil enhance productivity
by building up organic matter, by improving
aeration and by increasing water infiltration rates.
The residual effects of the greater organic matter
production are significant also in improving soil
aggregation.
Land use management appropriate to the
topography and rainfall, together with the
appropriate use of fertilizers, can make an
important contribution to soil conservation.
Reduced tillage cultivation practices
significantly reduce erosion; the proportion of
crop land subject to no-till techniques is
expanding rapidly in the USA and certain other
countries, for example in Brazil.

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18
Mineral Fertilizer Use and the Environment
6. Toxic substances
to several thousand p.p.m. The use in the
manufacture of phosphate fertilizers of phosphate
rock with a low cadmium content is one solution,
but the total supply is limited. This places the
emphasis on developing effective and viable
cadmium removal processes and research with
this objective continues.
Ultimately the solution could be a
combination of the removal of Cd in the
manufacturing process and farm management
strategies which minimize its potential entrance
into the food chain. The uptake of Cd by plants
can in fact be affected by many factors, such as
soil pH, moisture content, variety etc., which can
be controlled by the farmer.
There is no immediate urgency because, apart
from a few sites heavily polluted by industry, soil
cadmium levels are generally well below critical
levels. However, the existence of a medium and
long-term problem is recognized by the fertilizer
industry and studies and research on the subject
continue.
Phosphate fertilizers often contain small amounts
of elements which occur naturally in phosphate
rock and are carried through, in the
manufacturing process, to the finished product.
When the final product is a relatively high-value
material destined for use, for example, in the food
industry the potentially harmful elements are
removed, but to date economic processes for
removing these elements economically in
fertilizer production have not been found. Among
these elements, most attention has been paid to
cadmium (Cd).
There is evidence that Cd is slowly building
up in some soils. This is of concern because Cd is
not essential to plants or animals, and at high
levels can be toxic. Sources include atmospheric
deposition from industrial processes, sewage
sludges, animal manures and phosphate
fertilizers. In many European countries about
50% of total Cd input to agricultural soils is from
airborne sources. Sewage sludges contain
amounts of Cd which can vary from a few p.p.m.

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Mineral Fertilizer Use and the Environment