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The nitrogen surplus in agricultural areas of EU member states is illustrated in
Table 1.6.
Table 1.6 Nitrogen surplus in agricultural areas of EU Member States, 1990–1995
A factor contributing considerably to the nitrogen surplus is the decoupling of nutrient
cycles as a result of splitting agricultural production into animal and plant
production. When not subject to a limitation of livestock units per hectare, large
amounts of manure are produced in animal production and which may be no longer
used appropriately on the available land areas. Their use is seen more as a form of
waste disposal than a fertilisation measure. In general, farmers' valuation of farm
manure is poor because the availability of nitrogen is difficult to calculate and manure
has only an insignificant economic benefit owing to its low nutrient content. This
results in incorrect usage such as inadequate application techniques and excessive
quantities that are inappropriate to crop production and ecology (Döhler, 1996). An
example of this is over-application of nitrogen fertiliser in Beijing as described by
Steinbuch et al. (1993) (in Zhang et al., 1996). The amount of fertiliser applied for
vegetable production reached 3,719 kg N ha –1 and the nitrogen surplus was 3,206 kg
N ha –1 . The problem of over-application is further enhanced by preferentially
applying farm manure to types of crops that are not adversely affected by an
oversupply of nitrogen, such as maize, rape and root crops (Bach et al., 1992).
Figure 1.7 shows the relation between agricultural yield, the quantities of nitrogen
fertiliser used for producing these yields, the associated nitrogen emissions and the
foodstuff supply situation in industrialised countries (Isermann, 1994a).