Water Resources and Land Use — Some Agricultural Aspects

Abstract

The supply of water is one of the major factors which controls the growth of crops, and, hence, our food supplies. Agricultural aspects thus have an obvious place in any broad discussion of water management and land use.

The behaviour and use of water in the soil/plant system are briefly reviewed in the opening section. In temperate countries, such as Britain, deficient water in summer and excessive water in winter can both impose restraints. Irrigation and land drainage can thus both be necessary.

The later part of the paper is concerned with an environmental aspect which has lately received much attention — namely the leaching of nitrate which may enter water supplies. The cultivation of land inevitably creates the opportunity for nitrate to be leached; this occurs when no fertilizers are employed but their use can increase it. Agriculturalists and water engineers are equally concerned with minimizing these losses.

Recent suggestions that increasing fertilizer use in the last few decades will inevitably lead to larger concentrations of nitrate in water; in the future, are shown to rest on inconclusive observations. Much further hydrogeological work is desirable.

Finally, sources of nitrate in the total intake of the population and of children are examined; it and also nitrite are present in many foodstuffs. Representative survey data are limited but it appears that the content of nitrate in foodstuffs has changed little since fertilizers became widely used; moreover, even if drinking water were to contain 50 mg nitrate per litre it would not necessarily be the major source of nitrate in the total intake.

The assessment of risks to the health of the population which could result from ingesting nitrate or nitrite is the province of medical epidemiologists and thus outside the scope of the paper. However, it is evident that if it were judged necessary to define criteria for the protection of the population the subject should be considered on a much broader basis than that which led to the currently proposed limits of nitrate in water supplies.