Bermudagrass-Legume Mixtures As an Option to Reduce N Fertilizer Use in Hay Fields.

Nitrogen (N) fertilization can potentially increase bermudagrass yield in North Florida hay fields. Combination of sandy soils, low water holding capacity, high infiltration rates, high rainfall intensity, and excess of soil N might lead to N losses via nitrate leaching. Nitrate reaching the groundwater becomes a contaminant. Atmospheric N₂-fixation by forage legumes is a potential alternative to reduce N inputs. This study evaluated the performance of ‘Tifton-85’ bermudagrass (Cynodon spp.) mixed with rhizoma-peanut (RP; Arachis glabrata Benth.) or alfalfa (Medicago sativa L.) in contrast with their monocultures. A randomized complete block design with six treatments and four replicates was used. Treatments were: 1) bermudagrass monoculture; 2) bermudagrass monoculture + 90 kg N ha^-1 harvest^-1; 3) RP monoculture (‘Florigraze’); 4) alfalfa monoculture (‘Alfagraze 600 RR’); 5) bermudagrass + RP + 45 kg N ha^-1 harvest^-1; and 6) bermudagrass + alfalfa + 45 kg N ha^-1 harvest^-1. Plots measured 3 x 6 m and samples were harvested in area of 0.5-m² at 7.5 cm every 5 wks., from March to October 2016. Response variables included herbage acumulation (HA), botanical composition (BC), total above ground N, %N derived from atmosphere (%Ndfa), Biological N₂-fixation (BNF), and crude protein (CP). There were treatment, sampling date, and treatment x sampling date effects (P<0.0001) for HA. N fertilized bermudagrass HA was 4560 kg ha^-1 harvest^-1 and differ from the mixtures (P<0.05; 3530 and 2140 kg ha^-1 harvest^-1 for Bermudagrass/RP and Bermudagrass/Alfalfa, respectively) in May. Thoughout the season, fertilized bermudagrass had the greatest yield (P<0.05; 2068 kg ha^-1 harvest^-1). Mixtures averaged 1515 kg ha^-1 harvest^-1 and did not differ among them (P>0.05). Unfertilized bermudagrass, alfalfa, and RP monocultures were the least productives, yielding 916, 648, and 350 kg ha^-1 harvest^-1, respectively. N fertilized bermudagrass outyielded  other treatments, however the mixtures may fit better in a low input system.