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

7.2.2. Inland waters
Under temperate conditions, in inland fresh
water, P is usually the limiting nutrient and very
low concentrations can cause problems of
eutrophication. Surface water can be enriched
with P from both point (e.g. sewage treatment
works) and diffuse (e.g. agricultural land) sources.
As the amount of P from point sources has
declined in recent years, the percentage
contribution from diffuse sources has increased.
Although it has been generally accepted that
most soils fix P strongly, only very small amounts
of P have to be lost from soil to maintain the
concentration of P in drainage at levels likely to
cause environmental problems.
Phosphate in the soil is rather immobile and
the loss of water-soluble phosphate through
leaching is usually very small (less than 1 kg of
P
2
O
5
per hectare per year). Ignoring crop
removal, the two primary pathways of loss of
phosphorus from the soil are by erosion (wind
and water) and in run-off. Under European
conditions, the excessive surface applications of
animal manures can result in significant losses in
particulate matter in run-off. Areas where
intensive animal husbandry is practiced may
experience the addition of excessive amounts of
phosphorus to the soil, usually in the form of
heavy applications of animal waste eg. slurry or
farmyard manure. Under these conditions, soils
can have such a high content of phosphorus that
losses may increase.
In tropical lakes, there is evidence that
nitrogen can be the limiting nutrient. Phosphate
concentrations in the water are often higher than
in temperate regions while inputs of N from
surrounding land may be low.
Surface runoff (including soil erosion) from
cropland, pasture and forest, can contribute to
phosphate loading of surface waters. Best
management practices are highly effective in
eliminating this possibility and, at the same time,
allow for the most efficient use of crop
fertilization.
7.3. Potash
Unlike nitrogen and phosphate, potash has no
known deleterious effect on the quality of natural
waters (J.K. Syers, 1998).

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Mineral Fertilizer Use and the Environment