Performance and environmental effects of forage production on sandy soils. I. Impact of defoliation system and nitrogen input on performance and N balance of grassland

Grassland and its management is central to the productivity of and nitrogen (N) losses from dairy farms in north-west Europe. Botanical composition, production and N surplus of grassland were assessed during five consecutive years. The experiment consisted of all combinations of five defoliation systems: cutting-only (CO), rotational grazing (GO), grazing + one (MSI) or two silage cuts (MSII) and simulated grazing (SG). Four mineral N fertilization rates (0-300 kg N ha(-1) year(-1)) and two slurry levels (0 and 20 m(3) slurry ha(-1) year(-1)) were applied. Fertilizer N was more efficient in producing net energy (NEL) in grazing-dominated, low white clover systems (GO and MSI systems: 70 and 88 MJ NEL kg(-1) N) than in white clover-rich systems (MSII, CO and SG systems: less than or equal to60 MJ NEL kg(-1) N). While sward productivity in system MSI was similar to that in system GO, system MSII benefited from increased N-2 fixation at low N rates. There were small differences in NEL concentrations of the herbage between defoliation systems. Crude protein concentration of the herbage increased with increasing N supply from fertilizer, excreta and N-2 fixation. N surpluses (-63 to +369 kg N ha(-1) year(-1)) increased with increasing grazing intensity and increasing N fertilization rate. The average response in N surplus applied was 0.81, 0.59, 0.40, 0.33 and 0.24 kg N ha(-1) in systems GO, MSI, MSII, CO and SG respectively.