Agronomic performance and nutritive value of forage legumes in binary mixtures with perennial ryegrass under different defoliation systems

Abstract

SUMMARYProtein in forage legumes is often poorly utilized by ruminants and high nitrogen (N) losses are expected. The objective of the present study was to investigate the effects of forage legumes (white clover, WC; red clover, RC; lucerne, LG; and birdsfoot trefoil, BT) in binary mixtures with perennial ryegrass (G) under different defoliation systems (silage, simulated grazing and grazing) on agronomic performance and forage quality. A high proportion of legumes may favour dry matter (DM) yield and the defoliation system may reduce the persistence of certain forage legumes, with a negative influence on the energy and N yield. Annual DM yield under grazing was highest for WC mixtures (WC+G, 1059·2 g DM/m²) compared to all other mixtures, confirming its adaptation to grazing. Mixtures with RC (RC+G) and LG (LG+G) performed similarly to WC+G, whereas BT mixtures (BT+G) were less competitive under more intensively used systems. Analyses of crude protein, cell wall characterization and protein fractionation showed a three-way interaction between year, mixture and defoliation system. RC and BT resulted in a positive protein quality of the mixtures, probably due to their content of secondary plant compounds. In conclusion, different forage legumes did not perform equally in the cutting and grazing systems, and both legume species and defoliation systems interacted in the production of forage of high protein quality for ruminant nutrition.