Legumes in grassland can increase locally grown protein in fodder while reducing the nitrogen (N)-fertilizer requirements. Although the benefits of forage legumes are known, there was a decline in their use in the past due to inexpensive N-fertilizer, soya products from abroad, and variable legume persistence. In recent years, mounting environmental concern has sparked new interest in legumes. To quantify the effect of legume reseeding and N-application on permanent grassland on crude protein (CP) and dry matter yield (DM), a multifactorial trial was set up. Factors considered were clover species (red clover, white clover), N-application rate (0–170 kg N ha−1), N-fertilizer type (mineral-N, organic-N), and cutting management (3, 5-cut). Legume percentages were scored, and DM- and CP-yield was measured for three years. Crude-protein gains after legume reseeding were considerable and between 2.5–3.4 after red clover and 0.4–1.7 t CP ha−1 3 years−1 after white clover-reseeding even when compared to the control-high-N treatment. Legume percentages were negatively correlated to N-rates down to rates as low as 42 or 85 kg N ha−1 for a three- or five-cut management, respectively. Nitrogen-applications increased the yield (DM, CP) of control plots, whereas for legume-reseeded plots yield remained unchanged or was reduced. Differences due to N-fertilizer type were small or non-existent. Reseeding of clover was shown to be a viable method to increase crude protein in permanent grassland for about three years (red clover) and possibly beyond (white clover)
