Whereas positive effects of fertilizer use on the environment are often overlooked, attention nowadays is focussed on negative aspects. Mineral and organic fertilizers are accused of:

• accumulation of dangerous or even toxic substances in soil from fertilizer constituents, e.g. Cd from mineral phosphate fertilizers or from town or industrial waste products;
• eutrophication of surface water, with its negative effect on oxygen supply (damaging to fish and other forms of animal life);
• nitrate accumulation in ground water, thus diminishing the quality of drinking water;
• unwanted enrichment of the atmosphere with ammonia from organic manures and mineral fertilizers, and with N₂O from denitrification of excessive or wrongly placed N fertilizer.

As to contamination of soils with toxic heavy metals, it can easily be shown that mineral fertilizers make only a rather small contribution in comparison with, for example, town wastes. However, as soil fertility must be considered in the very long term and not only in decades or centuries, the annual addition should be kept at such a low level that the enrichment is negligible. Industrial waste products should always be carefully checked to determine whether they contain potentially toxic substances, and appropriate critical limits should be established.

Nutrient losses from the soil into surface and ground water (mainly nitrate by leaching and phosphate by erosion) occur even when fertilizers are not used, but they are increased slightly but unavoidably even by correct fertilizer use and are increased substantially by excessive or unbalanced use, which can be avoided.

Considerable leaching of nitrate is caused, for example, by:

• excessive application of organic liquid manure;
• intensively fertilized speciality crops;
• ploughing of grassland
• fertilizer application for over-optimistic yield expectations which fail to materialize (thus resulting in a surplus at the end of the vegetation period);
• part of the correctly estimated N requirement remaining unused because of other limiting factors not being taken into account, e.g. deficiencies of secondary or micronutrients.

In other words, N losses are mainly due to mistakes in fertilizer use or crop management, not to fertilizer use itself. Moreover, counter-measures can be taken to prevent loss of nitrate residues after harvesting (soil must not be left bare over winter) and to prevent soil erosion.

N loss by leaching seems to range from 10 to more than 100, in extreme cases more than 150 kg/ha N depending on the accuracy of fertilizer use and the extent of the preventive methods used. In Germany, at present the average appears to be far below the officially (but wrongly) discussed figure of 100 kg/ha N, but for most soils rather in the range of 30-60 kg/ha N. In any case, exaggerated overall averages do great injustice to farmers who apply fertilizers accurately and spend much effort in preventing excess leaching. From a scientific point of view, much more attention needs to be given to the enigma of N balance sheets before drawing premature conclusions on N losses.

Loss of phosphate by leaching (< 1 kg/ha P) is negligible, while loss by erosion is due to bad soil management rather than fertilizer use.

Atmospheric pollution by ammonia is mainly due to primitive methods of storing and spreading organic manure. N immission (involuntary intake from the air) ranges, in Central Europe, from 10 to 15 kg/ha N, with over 40 kg/ha N recorded in the vicinity of intensive animal husbandry.

Of the mineral fertilizers, only urea and ammonium sulphate might cause significant NH₃^- volatilization losses, especially if not incorporated (e.g. grassland, topdressing of cereals). To minimize these losses, incorporation into the soil or application before rain or irrigation is recommended.

The contention that agriculture contributes considerably to N₂O production via denitrification, as a result of excessive or wrongly applied fertilizer N, is a serious problem, because this gas contributes to the destruction of the ozone layer in the stratosphere which protects against ultra-violet radiation. Official estimates, derived mainly under artificial conditions or by the difference method, showing losses of approximately 15 % or more of the applied N, are not really substantiated; total denitrification losses in the range of 5-10 % of the applied N, of which only about 10 % is as N₂O, seem to be more realistic, especially for soils under normal moisture conditions.

Since pollution of the environment should be minimized, governments are trying to control the avoidable negative influences by special laws.

Further reading

AGRICULTURAL GROUP, NORSK HYDRO: Agriculture and Fertilizers. Norsk Hydro, Oslo, Norway (1990)

BEER, K.; et al.: Organische und mineralische Düngung. Deutscher Landw.-Verlag, Berlin, Germany (1990)

BENTON JONES, J.; et al.: Plant Analysis Handbook. Micro-Macro International Inc., Athens, Georgia, USA (1990)

BERGMANN, W.: Ernaehrungsstoerungen bei Kulturpflanzen. Fischer, Jena, Germany (1988)

BUCHNER, A.; STURM, H.: Gezielter düngen. DLG-Verlag, Frankfurt, Germany (1985)

CEA: Handbook on Environmental Aspects of Fertilizer Use. Centre d'Etude de l'Azote, Zurich, Switzerland (1983)

CHAPMAN, H.D.: Diagnostic Criteria for Plants an Soils. University of California, USA (1966)

COOKE, G.W.: Fertilizing for Maximum Yield. Granada, London, UK (1982)

COTTONIE, A.: Soil and Plant Testing. Soils Bull. 38/2, FAO Rome, Italy (1980)

DE GEUS, J.G.: Fertilizer Guide for the Tropics and Subtropics. Centre d'Etude de l'Azote, Zurich, Switzerland (1973)

ENGELSTAD, O.P.; DINAUER, R.C. et al.: Fertilizer technology and use. Soil Sci. Soc. America, Madison, USA (1985)

FAO: Maximizing Fertilizer Use Efficiency. Fertil. Plant Nutr. Bull. 6, FAO Rome, Italy (1983)

FAO: Fertilizer and Plant Nutrition Guide. Fertil. Plant Nutr. Bull. 9, FAO Rome, Italy (1983)

FAO: Manual on fertlizer distribution. Fertil. Plant Nutr. Bull. 8, FAO Rome, Italy (1985)

FAO: Fertilizer Strategies. Land and Water Devel. Ser. 10, FAO Rome (1987)

FAO: Fertilizer Yearbook, Vol. 38. FAO Rome, Italy (1988)

FAO: Fertilizer and Food Production. FAO Fertilizer Programme, Rome, Italy (1989)

FINCK, A.: Fertilizers and Fertilization. Verlag Chemie, Weinheim, Germany (1982)

FINCK, A.: Duengung. Ulmer, Stuttgart, Germany (1991)

FOLLETT, R.H.; MURPHY, L.S.; DONAHUE, R.L.: Fertilizers and Soil Amendments. Prentice-Hall, Englewood Cliffs, (1981)

IFA: Glossary of Fertilizer Terms. IFA, Paris, France (1980)

JONES, U.S.: Fertilizers and Soil Fertility. Reston, Reston (1979)

KATYAL, J.C.; RANDHAWA, N.S.: Micronutrients. Fertil. Plant Nutr. Bull. 7, FAO Rome, Italy (1983)

KLUGE, G.; EMBERT, G.: Das Duengemittelrecht (German Fertilizer Law). Landwirtsch.-Verlag, Muenster, Germany (1989)

MENGEL, K.; KIRKBY, F.A.: Principles of Plant Nutrition. Int. Potash Inst., Bern, Switzerland (1987)

MORTVEDT, J.J.; et al.: Micronutrients in Agriculture. Soil Sci. Soc. America, Madison, Wisconsin, USA (1972, new edition 1991)

REUTER, D.J.; ROBINSON, J.B.: Plant Analysis. Inkata, Melbourne, Australia (1988)

ROBINSON, J.B.D. (ed.): Diagnosis of Mineral Disorders in Plants. Her Majesty's Office, London, UK (1983)

SILLANPAA, M.: Micronutrient Assessment at Country Level. Soils Bull. 63, FAO Rome, Italy (1990)

SIMPSON, K.: Fertilizers and Manures. Longman, London, UK (1986)

SPRAGUE, H.B.: Hunger Signs in Crops. McKay, New York, USA (1951)

TFI: Fertilizer Handbook. The Fertilizer Institute, Washington, USA (1976)

TISDALE, S.L.; NELSON, W.L.; BEATON, J.D.: Soil Fertility and Fertilizers. McMillan, New York, USA (1985)

Even so, it has to be admitted that a significant proportion of the benefits to food quality are lost in processing, e.g. in the production of white bread, and may even be lost during cooking, as with some heat-sensitive vitamins.

In view of the established generally positive effect of fertilizer use on food quality, it is surprising that certain groups of consumers in the developed countries are requesting so-called "natural" food in the sense of food produced not only without chemical plant protection but also without the use of synthetic mineral fertilizers (quite apart from the entirely separate question of food additives such as preservatives and colourants).

A special market has been developed for such products of "organic farming" using either organic manure alone or together with "natural" mineral fertilizer such as rock phosphate. This is fully acceptable so long as scientific principles are observed and no unfounded claims are made for superior quality.