Agricultural effects on yield and nutritive value of grassland under a limited fertilisation rate on sandy soils in Flanders

From 1999 to 2002, we studied the yield production and quality parameters of grassland installed on sandy soils (1) under normal management (NM), (2) under management with respect to meadow birds (MBM) -first mowing date 15 June or later- and (3) under botanical management (BM) -first mowing date 1 July or later. The experiments were conducted at two locations, Aalter and Geel. The biomass production under MBM and BM decreased by resp. 19% and 46% as compared to the NM. The nitrogen content in the vegetation of the delayed first cut (without fertilisation) of MBM (2.4%) and BM (2.3%) was much lower than under NM (3.3%). Since the first cut makes the major part of the total annual dry matter yield (43% for MBM and 59% for BM), the average nitrogen content of the overall DM yield dropped substantially if the first cut was delayed. The same phenomenon occurred for the digestibility of the organic matter: overall 66% for MBM and 59% for BM as compared to 69% for NM. The digestibility was partially influenced by the botanical composition. MBM resulted in a shift in botanical composition, favouring Poa trivialis L., Ranunculus repens L., and Holcus lanatus L. as compared to NM. BM mainly favoured Holcus lanatus L., and Ranunculus repens L. as compared to NM. Under the management types with delayed first cut, problems with residual mineral soil N never occurred.