1. Stikstofbemesting van grasland en kwaliteit van het oppervlaktewater [Nitrogen fertilization of grassland and surface water quality];Alberda;Stikstof,1971
2. Council Directive of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources (91/676/ EEC);Anonymous;Official Journal of the European Communities,1991
3. Jungviehweiden: 100 kg N pro ha reichen! [Grassland for heifers: will 100 kg N per ha do!];Anonymous;Top Agrar,1999