The monitoring of nitrogen surpluses from agriculture

Nitrogen balances are calculated as a tool for monitoring national and regional losses of nitrogen to the environment. In the Netherlands 70% of the nitrogen losses occur in agriculture; mainly (70%) in soil and groundwater. Where measurements on emissions to the different environmental media are laborious and costly, calculations are made with models or statistics. This paper describes two methods to determine the total nitrogen surpluses from agriculture using statistical information: the farmgate and the soil surface method. Surpluses are defined as the difference between the nitrogen inputs into and outputs from the agricultural system. The methods described are used to monitor the effectiveness of nitrogen reduction measures taken on account of the EU Nitrate Directive and the OSPARCOM agreements. The methods of calculation described here are also used by OECD and EUROSTAT to compute indicators of nutrient use. Results from the Netherlands over a ten-year period indicate that so far little progress has been made in reducing nitrogen surpluses. Ammonia emissions have been reduced at the expense of an increased loss of nitrogen to the soil. Estimating nitrogen surpluses calculated as the difference between the inputs of nitrogen to the soil and the withdrawal by crops (soil surface method) requires consistent data on the feed-animal-manure balance. When comparing data on agricultural surpluses between different countries this consistency is a major concern.