Biological N₂ Fixation, Belowground Responses, and Forage Potential of Rhizoma Peanut Cultivars

Abstract

Grasslands in warm‐climate regions are often based on grass monocultures, increasing their dependence on N fertilizers. Integrating perennial legumes into grass pastures is a logical option. The objective of this 2‐yr study was to assess seven rhizoma peanut ( Arachis glabrata Benth) cultivars: Arbrook, Arblick, Ecoturf, Florigraze, Latitude 34, UF Peace, and UF Tito. Above‐ and belowground responses included biomass, in vitro organic matter disappearance (IVOMD), N concentration, N content, δ 15 N, proportion of N derived from atmosphere (%Ndfa), and biological N 2 fixation (BNF). Arbrook was more productive than Florigraze in both years ( P ≤ 0.05) but produced similar biomass to other varieties in 2014. In 2015, Arbrook also was more productive than Arblick and Latitude 34. Herbage N concentration ranged from 19.2 to 36.3 g kg −1 . Arbrook tended to be less digestible than other rhizoma peanut cultivars. The BNF represented >80% of herbage N and averaged 200 kg N ha −1 yr −1 , with values ranging from 123 to 280 kg N ha −1 yr −1 . Root and rhizome biomass varied among cultivars, with Ecoturf (26.9 Mg organic matter [OM] ha −1 ) and Latitude 34 (27.8 Mg OM ha −1 ) presenting greater root and rhizome mass than Florigraze (10.5 Mg OM ha −1 ) but similar to other varieties. Roots and rhizomes represented a significant portion of the total biomass and N pool, and further studies are needed to assess turnover of these tissues as well as their N contribution in grazing systems using grass–rhizoma peanut mixtures.