In situ degradation of perennial rye grass from grazed pastures during the season at two levels of nitrogen fertilization Christian Salaün, Wilfried M. van Straalen, Jan Kosut, Jean-Louis Peyraud and Ad M. van VuurenAnn. Zootech., 48 1 (1999) 35-46DOI: https://doi.org/10.1051/animres:19990104