Geography Reference
In-Depth Information
as nitrogen, phosphorus and potassium, to maintain good plant
productivity. Pesticides can often attack living things that they
were not intended for and can leach into groundwater and rivers.
Fertiliser use has increased tenfold over the last 50 years. This is
fine as long as it has been applied in the correct amount for the soil
and crop and at the right time of year so that it is not wasted and
simply washed out of the soil. However, river water, groundwater
and lakes have seen increased nitrate concentrations related to the
leaching of fertilisers. Nitrates in drinking water are a health hazard
and can damage river- and lake-based plants and animals.
Organic
farming
relies on biological processes for crop and livestock pro-
duction rather than using manufactured pesticides and fertilisers.
Practices such as crop rotations, varieties more resistant to disease,
use of plants that take nitrogen out of the atmosphere and applica-
tion of compost and manures are common in organic farming. As
yields tend to be lower than in conventional farming, food prices
tend to be greater, but clearly there is a balancing act between food
price and the wider price of environmental pollution through man-
ufacture of agrochemicals or potential pollution from leaching.
Intensive agriculture has reduced soil organic matter. Soils with
less than 1.7 per cent organic matter may be close to becoming a
barren landscape rather like a desert. This is known as
desertifica-
tion
. In the Mediterranean area 75 per cent of the landscape has a
low (3.4 per cent) or very low (1.7 per cent) soil organic matter
content and so desertification is a major cause for concern. Organic
matter content has been reduced by the abandonment of crop rota-
tion, ploughing up grasslands and the burning of stubble (vegeta-
tion remains after cropping). These all reduce the amount of
organic matter being returned to the soil. Reversing these actions
can allow some recovery of organic matter content (e.g. ploughing
stubble back into the soil rather than burning it and increasing the
proportion of grass cover).
Salinisation occurs when soluble salts of sodium, magnesium and
calcium accumulate so that soil fertility is reduced. This is mainly a
problem in warm, dry regions where evaporation and upward
movement of water in soils exceeds downward movement from
rainfall and percolation. Furthermore, irrigation of the land with
water of a high salt content (i.e. where a lot has evaporated before
being used so that the concentration of salts in the water is greater)
