Replacing synthetic N with clovers or alfalfa in bermudagrass pastures. 2. Herbage nutritive value for growing beef steers

Abstract

The objective of this study was to evaluate the effects of including alfalfa (ALF, Medicago sativa L.) or a combination of white (Trifolium repens L.) and red (Trifolium pretense L.) clovers (CLVR) inter-seeded into bermudagrass (Cynodon dactylon L. Pers.) on herbage nutritive value compared with monocultures of bermudagrass fertilised with 0 (0N), 56 (56N), or 112 (112N) kg nitrogen (N)/ha over four grazing seasons. At the end of the fourth year (during the winter), legume plants in ALF and CLVR were killed and the carryover N benefit on bermudagrass nutritive value was evaluated during the fifth year. Pre-grazing herbage of all pastures exceeded the dietary recommendations for growing steers to maintain 0.9 kg/day average daily liveweight gain for crude protein and total digestible nutrients, 118 and 617 g kg/DM, respectively. Post-grazing herbage in ALF was below 600 g/kg total digestible nutrients at all times during the grazing season, post-grazing total digestible nutrients of CLVR was below 600 g/kg during the late summer and autumn. Post-grazing herbage of monoculture bermudagrass pastures fell below 600 g/kg in the middle of summer regardless of N fertilisation. Carryover N benefits of legumes were similar to 112N in the early summer, but were not different than 0N and 56N during the late summer and autumn. Replacing applications of synthetic N in bermudagrass swards with inter-seeding of either clovers or alfalfa produce herbage with equivalent nutritive value to heavily N fertilised monocultures of bermudagrass during the early summer, and similar to moderately N fertilised in the late summer and autumn. The inclusion of legumes in bermudagrass swards can reduce the reliance on synthetic N fertilisation with little overall effect on herbage nutritive quality possibly decreasing environmental impacts of grazing production systems.