Permanent grassland and 3-year leys alternating with 3 years of arable land: 31 years of comparison

During 31 years (1969–1999), we measured the yields of permanent grassland and of 3-year temporary leys alternating with 3-year periods of arable forage crops. The average feed energy yields of both types of grasslands, respectively 75.1 and 73.3 GJ Net Energy for Lactation ha−1, were not significantly different. Possible preconditions for the lasting high production level of the 31-year old, never reseeded permanent pasture were the high fertilization level (200–350 kgN ha−1 year−1) and the preservation of a fairly good botanical composition. The temporary grasslands produced as much as the permanent grassland without the necessity to apply higher amounts of fertilizer N during their 3-year lifetime.