Because of the legume fixation capacity, their high protein content, digestibility and intake characteristics, more and more attention is paid to grassland clover content. In field experiments, clover content must often be determined, for example to quantify nitrogen flux or the best practices to manage such species (Stilmant et al., 2004). However hand sorting of clover and grass, even if accurate, is time-consuming and has a high labour cost. In comparison, accuracy of visual estimation of clover content, directly in the field, varies according to training and experience. Near-infrared reflectance spectroscopy (NIRS) has been proposed as a method for the rapid determination of sward botanical (Petersen et al., 1987; Pitman et al., 1991) and morphological composition (Leconte et al., 1999; Stilmant et al., 2005). This paper describes the performance of a NIRS calibration developed to characterise red clover (Trifolium pratense) content when associated to different grass species and this at different phenological stages
