Over-fertilization of agricultural lands

The Bekaá Valley in Lebanon.

Uncontrolled application of agrochemicals is a major environmental problem in the Arab region. Over-fertilisation with nitrate in highly productive agricultural areas, like the Bekaá valley in Lebanon may lead to groundwater pollution and eutrophication of rivers and lakes as well as contamination of crops with excess nitrate.

The agriculture in the Bekaá valley mainly focuses on field crops, vegetables, fruit trees and grapes. A mean annual rainfall of about 600 mm combined with irrigation from sewage water and some wells enable the farmers to grow several crops per year.

Inputs of more than 750 kg of nitrogen per ha in form of inorganic fertilizer per vegetation period are common in the vegetable production in the Bekaá valley. These rates are extremely high, even without the additional inputs of nitrogen through irrigation, precipitation and mineralization, which may sum up to an extra 250 kg of nitrogen per ha. At the end of the cropping season, in autumn 2002, more than 450 kg of nitrogen per ha was measured in some soils down to 50 cm depth (Figure 1). This amount may be leached into the groundwater during the winter month.

These extreme values are reflected by high nitrate concentrations especially in the shallow groundwater reaching up to 300 mg of nitrate per liter. In deeper aquifers the nitrate concentrations may still reach locally more than 100 mg of nitrate per liter. These high values represent a severe health risk for humans and livestock as groundwater is locally used as drinking water.

In many cases a reduction of nitrogen fertilization to half of the yearly rate combined with an appropriate selection of nitrogen forms, split up of the applications and an adapted timing according to the needs of the different plants would raise the economical outcome of the cropping considerably. This would also reduce - or maybe even avoid - the contamination of the groundwater and crops through over fertilization with nitrogen fertilizers.

In the Bekaa only few farmers dispose of an adequate education in agronomy which enables them to select and apply mineral fertilizers properly. The relative low costs of fertilizer are fostering the mal-use of nitrogen fertilizers.

A more efficient fertilizer management is required in the region - including modern techniques of soil nitrate monitoring - to alleviate the ecological damage, protect water resources from pollution and at the same time make agricultural production more profitable.

It is suggested to activate the agricultural extension services, in order to ensure appropriate fertilizer use through the farmers.