Demonstrationsvorhaben „Indikatoren zur Früherkennung von Nitratfrachten im Ackerbau“ - Studie „Messprogramme der Bundesländer und angrenzender EU-Staaten (NL, DK) zum Abgleich des Frühindikatorensystems“

Abstract

In the demonstration project „Indicators for the early detection of nitrate loads in soil under crop production”, data on nitrogen balances as well as mineral nitrogen concentrations in soil profiles and percolating waters are collected in five federal states of Germany with a total of 48 farms and 576 test sites. Data collections and analyses are conducted under consideration of strictly harmonised guidelines. The project aims at testing the early indicators to directly show the effects of adjusted agricultural practices on nitrate loads. Furthermore, the indicators are supposed to be transferred into a monitoring system. By this means, a temporal or spatial decoupling between adjustments of agricultural management practices and nitrate concentrations in ground water wells can be overcome. This might help to better achieve the goals of the EU Nitrates Directive. Such a monitoring concept requires a harmonised approach across the federal states to enable the comparability of the results across farms and test regions. The present study is a meaningful step stone of the demonstration project. It provides an overview on current activities in nitrate monitoring of the German federal states as well as Denmark and the Netherlands. Furthermore, relevant insights and results for the development and implementation of an early detection monitoring of nitrate loads by different indicators are highlighted.
Federal state ministries and associated professional authorities for agriculture and environment were interviewed and literature was reviewed. For a comparison of the monitoring activities with neighbouring EU member states, ministries of Denmark and the Netherlands were also involved. A special focus was laid on activities linked to the implementation of the EU Nitrates Directive, the EU Water Framework Directive and the EU Directive on the Quality of Water intended for human consumption as well as the German Water Ressources Act. Considering German monitoring efforts, insights and results are predominantly not available in peer-reviewed academic journals. The origin of information therefore is manifold, consisting of information from public authorities, legal obligations to report, professional articles, project reports, annual reports and internet articles or specialist’s presentations.
In all Federal states comprehensive efforts to investigate and assess the relationship between agricultural management and nitrate loads in leachate, drainage water, ground water, and surface water have been made or are in progress. In some Federal states especially the implementation of the EU Water Framework Directive led to an intensification of monitoring efforts, while other Federal States concentrate on monitoring networks already established for the implementation of the EU Nitrates Directive and the Federal Water Act. There are several different approaches utilised by the federal states to reach an early detection of nitrate loads by different indicators. Research projects, e.g. assessing regional pedo-geological and hydrological properties as well as the acquisition of agricultural data relevant for ground water quality, deliver valuable additive data for a target-oriented planning and conduction of measures for ground water protection. The federal states have collected comprehensive experience and knowledge for the applicability and use of different indicators in nitrate monitoring. Monitoring programmes mostly consist of both, calculative and analytical indicators. However, it must also be noted that the monitoring and research approaches often differ markedly between states regarding content alignment, state of work or methodical procedures. For example, some states conduct measurements of mineral nitrogen (Nmin) on large scales for quantifying residual nitrogen in soil in autumn, while other states concentrate on the assessment of nitrogen balances based on agricultural surveys and accountancy data. Sometimes these approaches are combined with the use of geo-hydrological model approaches at different spatial and temporal scales.
Nutrient balances allow to estimate nitrogen surpluses at diverse spatial scales, i.e., from the field over the farm towards whole agricultural regions, with comparably little effort. The predictive power of these balances depends markedly on the quality of the collected data and on the degree of data aggregation. However, even considering a field-specific assessment of nitrate loads from nitrogen balances, results of some states show a sufficient relationship to nitrate concentrations in ground water only, if long time data series are available. The comparably low correlation of single-year data is mainly attributable to the year-specific interactions of agricultural practices, weather and soil conditions and the underlying nitrogen dynamics in the soil.
In most states, Nmin-measurements in autumn are part of monitoring programmes at the field scale and to lesser extend at the regional scale, too. Nmin-measurements can be conducted with comparatively little effort and the values include year-specific information on nitrogen dynamic. Considering the amount of percolating water, Nmin values can be used to predict nitrate concentrations in leachate. However, for these predictions, the Nmin-method is not necessarily reliable under all possible site conditions. Furthermore, timing and method of sampling, as well as the way of transport, storage, and analysis need to be specified to ensure comparability of measured values. These methods and conditions sometimes differ between states.
Depth profiles of nitrate are used for monitoring purposes at representative sites by several states in addition to Nmin-root-zone measurements.. Nitrate measurements in the leaching zone are suitable for illustrating nitrate loads from recent years and enable the validation of calculated nitrate loads from Nmin-measurements. Furthermore, suction plates or suction cups as well as lysimeters are used for more exact measurements of nitrate concentrations in leachate in experiments but for monitoring purposes, too. Although, these measurements provide exact data on nitrate leaching at a certain site, a large-scale representative monitoring is practically not feasible due to the high technical efforts.
The results from the federal states and the neighbour states, The Netherlands and Denmark indicate that an efficient nitrate monitoring should be ideally based on both, calculative (N-balances) and analytical indicators (e.g. Nmin-measurements and nitrate depth profiles) surveyed from representative farm networks and according to standardised methods. Additionally, these data should be used in process-based as well as aereal material-flow models.
With the present demonstration project, a combined and harmonized approach of calculative and analytical procedures is created, which can illustrate the actual status of nitrate pollution reliably and provides helpful information for nitrate reporting. To achieve this objective, the indicator system of the demonstration project should be applied in additional test regions with other agricultural structures and site conditions to proof the adequacy of the monitoring concept.