Adoption of Alfalfa in Florida: Effects of Stubble Height and Cultivar on Yield and Persistence.

Alfalfa (Medicago sativa L.) is the most important forage crop in the world due to its high yield and nutritive value. In 2016, 48.7 million tons of forage were derived from alfalfa and alfalfa/grass mixtures in the USA. Florida livestock production systems depend on alfalfa importation; therefore, there is a need to develop alfalfa cultivars grown under proper management practices. The objectives were to study the effects of two stubble heights (5 and 10 cm) on yield, root/shoot development and persistence of four alfalfa varieties. The following varieties “FL77”, “FL99”, “Bulldog 805” and “AmeriStand 901 TS” were evaluated for two years in a split plot design with six replicates in Citra, FL. Plots were harvested at alfalfa growth stage of 1/10 bloom (32-40 day intervals) for a total of 24 harvests. At the end of the study, plant density, crown diameter, number of tillers and root weight were sampled in a 0.25 m² quadrant. Across the experiment, average dry matter (DM) production was 7.8 ton ha^-1 y^-1. Stubble height did not show significant effect on DM production, but a significant cultivar effect was observed (p<0.05). The local variety FL99 yielded 11.5% more forage than the other cultivars. Stubble height significantly affected plant density; plant density was double for alfalfa harvested at 10 cm vs 5 cm. Stand persistence showed a significant cultivar effect; the cultivar FL99, followed by Bulldog 805, showed higher plant density. The cultivar FL99 also exhibited the highest root weight and crown diameter. Results suggest that plant persistence is a character to improve for Florida conditions. Broad genetic diversity was observed among this small set of cultivars suggesting that there is a potential to improve alfalfa productivity and persistence through breeding.