Herbage responses and nitrogen agronomic efficiency of bermudagrass–legume mixtures

Abstract

Bermudagrass (Cynodon spp.) is an importantwarm‐season grass for livestock in the southern United States. To be productive, bermudagrass requires supplementary N. This 2‐yr study assessed whether N fertilization could be halved by introducing alfalfa (Medicago sativa L.) or rhizoma peanut (RP; Arachis glabrata Benth.) into ‘Tifton‐85’ bermudagrass monocultures without compromising productivity. Treatments were: bermudagrass, N‐fertilized bermudagrass, alfalfa (‘Alfagraze 600 RR’), RP (‘Florigraze’), and the mixtures bermudagrass–alfalfa and bermudagrass–RP. Mixtures were fertilized with 45 kg N ha–1 harvest–1, whereas N‐fertilized bermudagrass received 90 kg N ha–1 harvest–1. Seven harvests were made each year. Nitrogen‐fertilized bermudagrass and mixtures had similar total herbage accumulation (HA) in 2017, but mixtures produced approximately 3,340 kg DM ha–1 yr–1 less than N‐fertilized bermudagrass in 2016, which had a drier summer. Percentage of alfalfa in the mixtures decreased from 68 to <1% by the end of the study. Rhizoma peanut proportion in mixtures was often low (max. 8%). Nitrogen‐fertilized bermudagrass had the greatest total harvested N in May of 2016 (96 kg N ha–1), but it did not differ from bermudagrass–RP in May of 2017. Nitrogen agronomic efficiency (NAE) was greater for mixtures (27.5 kg DM kg–1 N applied) than for N‐fertilized bermudagrass (21 kg DM kg–1 N applied). Greater NAE in mixtures occurred due to limited response to high N fertilization rates in the N‐fertilized bermudagrass. Further studies on establishment methods, cultivar selection, and management practices are still needed to adopt a successful bermudagrass–legume mixture in northern Florida.