Environmental Management: Principles and practice

Chemical fertilizers
Once agriculture relied on livestock and human manure, compost, bonemeal, dried
blood, green manures, marl, agricultural lime and crop rotation. Work in the UK by
Lawes, Gilbert and others, and in Germany by Von Liebig, led by the 1840s to the
development of superphosphate artificial fertilizer. Between 1885 and 1985 the UK,
one of the earliest countries to adopt artificial fertilizer widely, increased applications
25-fold (Briggs and Courtney, 1985:34, 101). After 1945 combined nitrogen-
potassium-phosphate (NPK) fertilizer use in the UK increased considerably. The
same period also saw changing agricultural practices, leading to reduced use of animal
manure and agricultural lime, more mechanization and less input of manual labour.
In the 1930s UK agriculture could not feed the population; between 1952 and 1972
UK agricultural output rose by about 60 per cent and now feeds a much larger
population, largely thanks to artificial fertilizers, although changes in the crops grown
make it difficult to assess how much.
On a world scale, fertilizers, particularly N-fertilizers, have played a key role
in increasing crop production (Pinstrup-Andersen, 1982:148). Because of the diversity
of factors involved, it is difficult to be sure how much is attributable to improved
crops. In 1950 the world used about 14 million tonnes of N-fertilizer; by 1985 this
had risen to about 125 million tonnes (Saull, 1990). In the late 1970s on average the
developing countries used 28 kg ha
–1
and the developed countries 107 kg ha–1. Most
of the fertilizer used in developing countries is for large-scale grain and export crop
production. Boserüp (1990:40) noted that in 1970 80 per cent of India’s chemical
fertilizer was used by only 15 per cent of districts; it is therefore probably reasonable
to say that most developing country farmers use little or no chemical fertilizer. Japan’s
success in modernizing its agriculture and the roughly one-third increase in food
production in China between 1970 and 1985 are attributed largely to fertilizer use
(Allen, 1977; Wolf, 1986:12).
The world’s food and commodity production is clearly dependent on chemical
fertilizers, and their use is likely to increase, but unfortunately they can be a serious
source of pollution. In addition, there are uncertainties about the long-term impact
of chemical fertilizers on farmland. There is some indication that where year-round
use of monocrops and fertilizer has replaced crop rotation and use of livestock manure,
fertility problems arise, in particular a net loss of organic matter from the soil, and in
some areas zinc or sulphur deficiency.
Some countries have moved away from mixed agriculture for commercial
reasons so that arable and livestock farming are no longer integrated—the former
must rely on chemicals and the latter have an animal waste disposal problem. The
costs of disposing of agriculture waste may one day bring agriculture full circle, to
recycling livestock manure and crop residue, possibly together with domestic refuse

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and human sewage. But to do so will require composting facilities and distribution.
An alternative is to incinerate these wastes and recover electricity and district heating
(as in Denmark).
Artificial fertilizers offer the following advantages over organic fertilizers:
♦
They can be easier to store, handle, apply and transport than most natural
fertilizers in use at present.
♦
There is less smell, lower risk of pathogenic contamination (although well-
composted organic material is virtually pasteurized).
♦
Land spread with manure cannot be properly grazed for some time due to the
risk of disease transmission and because cattle dislike unclean pasture. Artificial
fertilizers allow intensive use of grazing land more rapidly after treatment.
If they are not applied with caution, artificial fertilizers cause contamination
(fertilizers are contaminants rather than pollutants) and fail to give their full potential
(Mellanby, 1970; Gunn and Stevens, 1976). Both organic manures and artificial
fertilizers can cause eutrophication of water bodies and increased nitrates in
groundwater.
Phosphates have been accumulating in soils, river and lake sediments for
decades, as a consequence of the use of phosphatic fertilizers, spreading of livestock
manure, disposal of sewage and leaching of poorly sealed landfill sites. This poses a
threat, particularly in Europe and North America. Studies in Europe suggest that,
even if application of phosphates is controlled, steady leaching and possibly more
rapid mobilization if there is soil acidification or global warming will lead to a six-
to ten-fold increase in river and groundwater contamination. Such levels would raise
problems for domestic water supply and for the ecology of rivers, lakes, the Baltic,
the North Sea and other seas (Behrendt and Boekhold, 1993).
Excessive levels of nitrates (NO
3
) in groundwater and surface water are
increasingly a problem in Europe, the USA and other parts of the world. The
indications are that it is N-fertilizers which are responsible for a good deal of
contamination, which may also be caused by more deep ploughing, use of detergents,
sewage pollution, conversion of pasture to arable or land drainage. In parts of the
USA irrigation using N-fertilizers seems to be a major cause of groundwater nitrates.
In the UK borehole studies suggest correlations between conversion of pasture to
arable with N-fertilizer use and high groundwater nitrate levels (Conway and Pretty,
1991:186). In 1991 between 30 per cent and 35 per cent of the UK population
depended on groundwater, which in some areas is increasingly contaminated.
There are ways of controlling nitrate fertilizer use: reduction of price supports
for crops; regulation of crops grown; quotas or permits which seek to limit expansion
of an activity; set-aside—the withdrawal of land from production; taxation of nitrate
fertilizers (Clunies-Ross, 1993). Even if such controls were adopted, improvement
would come slowly because nitrates may take up to 50 years to reach groundwater,
depending on the geology (Hornsby, 1989). Conversion of farmland to some other
use could, because agricultural liming ceases, lead to increasing soil pH and greater
releases of nitrates, phosphates and heavy metals. Costly slow-release liming treatment

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may be needed. In temperate environments, planting winter wheat with white clover
might help to reduce nitrate leaching, and would cut costs of fertilizer inputs and
discourage pests. Authorities will be forced to treat domestic water to remove nitrates,
blend contaminated and pure supplies or store water in surface reservoirs for long
enough to reduce nitrate content.