Assessing agriculture’s impact on the environment

One of the measurements used to assess the impact of agriculture on the environment is the nutrient balance of nitrogen usually expressed in kilograms of nitrogen per hectare.

It estimates the potential surplus of nitrogen on agricultural land, by calculating the balance between nitrogen being added to the land and nitrogen being taken out. The input of nitrogen includes fertilisers and animal manure as well as nitrogen-fixing by legumes and deposits from the air. Nitrogen output is contained in harvested crops, or crops eaten by livestock.

The measurement gives an indication of the potential for nitrates to leach into the groundwater (see page 26). Where there are high levels of application of mineral and organic fertilisers, there is also the possibility of ­polluting the air with ­emissions of ammonia and nitrous oxides.

According to figures from the European Environment Agency in a report published last year, the balance of ­nitrogen declined between 1990 and 2000 from an average of 66kg/ha to 55kg/ha for the EU15 states, a ­generally improving picture.

But in some parts of the EU, the levels are much higher: the Netherlands has the worst balance (226kg/ha), followed by Belgium (174), Luxembourg (117), Germany (105) and Denmark (77). The levels are lower in most Mediterranean countries, chiefly because there are much lower levels of livestock production.

The EU has passed two pieces of legislation relevant to the nitrogen balance. The 1991 nitrates directive aims to reduce water pollution caused by nitrates from agricultural sources and sets limits on the amount of livestock manure that can be applied to the land. The water framework directive requires that inland and coastal waters are in good ecological status by 2015.

One of the measurements used to assess the impact of agriculture on the environment is the nutrient balance of nitrogen usually expressed in kilograms of nitrogen per hectare.