environmental problem associated with fertilizer use is
contamination of water with nitrates and phosphates.
The nitrogen from
fertilizers and manures are eventually converted by bacteria in the
soil to nitrates. These nitrates can be leached into the groundwater
or be washed out of the soil surface into streams and rivers. High
nitrate levels in drinking water are considered to be dangerous to
Phosphorus cannot be
readily washed out of the soil, but is bound to soil particles and
moves together with them. Phosphorus can therefore be washed into
surface waters together with the soil that is being eroded. The
phosphorus is not considered to be dangerous, but it stimulates the
growth of algae in slow moving water. These algae eventually die and
decompose, removing the oxygen from the water causing fish kills.
This process is called eutrophication.
It is important to
remember that there are a number of sources of these pollutants
including industrial waste, sewerage disposal, detergents and
manures. The problem of high nitrate levels in groundwater was
recorded as early as 1860, long before fertilizer use became
shows that the main sources of nitrates in groundwater are crop
residues and organic matter that decompose and produce nitrates at
time when crops cannot make use of them.