Reduction of Nutrient Losses from Vegetable Cropping in Water Protection Zones in Baden-Württemberg, Germany

Keywords: nitrogen, nitrate pollution, water protection, vegetables, SchALVO, fertiliser ordinance, Düngeverordnung, monitoring success.

In Germany the Fertiliser Ordinance (Düngeverordnung, DüV) describes the standards of good agricultural practice of fertilisation and implements the EU-Nitrate Directive in national law. The DüV was amended in 2017 and 2020. The basic rules of DüV are strengthened in water protection areas (WPAs) in each of the 16 states of Germany. The organisation of these tightened measures differs between decentralised contracts of water companies with farmers and national decrees. Baden-Württemberg (BW) had decided to establish regulations and settlement of claims in WPAs centrally managed by the state government. This was due to the fact that WPAs account for 26% of the state area, with 1,250 independent water supply companies. Thus agriculture and horticultural practice in BW is subject to the centrally organised decree of SchALVO (Schutzgebiets- und Ausgleichsverordnung).

The SchALVO fulfils the Water Framework Directive as an ‘additional program of measures’. The SchALVO is compulsory in WPAs, with 359,500 ha in agricultural use. The constraints depend on soil type, distance to water source and the nitrate concentration of groundwater in three classes (I <35-50, II 35-50, III >50 mg NO3 L-1). Measures in vegetable cropping include fertiliser use, fertiliser splitting, crop choice, fixed greening dates, time windows for tillage and others. To monitor the implementation of the measures, soil samples are taken for nitrate-N in the 0-90 cm depth range, between October 15th and November 15th. Farmers receive financial compensation for meeting a threshold of 45 kg N ha-1.

Until 2000 monitoring was done in WPAs of all classes. After amending the SchALVO in 2001 control was restricted to areas at risk (nitrate class II and III). This concentration on areas with higher nitrate-N concentration in groundwater corresponded with an increase of residual nitrate-N. Since 2006 the residual nitrate-N for vegetable crops has varied between 70 to 80 kg N ha-1 and exceeded the values of arable crops.

In 2019 a detailed analysis of nitrate-N residues on roughly 150 vegetable growing sites was carried out and the results presented. Generally the success of measures according to SchALVO to reduce nitrate-leaching depend on proper sampling, as well as site specific characteristics, weather conditions and crops. The results of the monitoring program are used to check compliance with the requirements and are a valuable instrument of the extension services to derive recommendations for practice.

Karin Rather, State Horticultural College and Research Institute (LVG), Heidelberg, Germany

13 pages, 3 figures, 7 tables, 5 references