Pacific Agriculture and Natural Resources

There is a need to select high quality forage legumes that are acid soil-tolerant, drought resistant, and persistent under the close defoliation associated with intensive pasture systems in the humid tropics. A greenhouse pot study was conducted to determine forage legume seedling growth (10 week-old) and regrowth (5 weeks after clipping to an 8-cm residual stubble) responses of ‘Amarillo’ perennial forage peanut (PFP, Arachis pintoi Krap. & Greg.) and barrel medic (Medicago truncatula Gaertn.) accessions W6 6037 (M37) and W6 6092 (M92) to Honolua silty clay (Ustic Palehumults) and Kokee silty clay loam (Alic Hapludands) soils at pH 4.6 and 5.6. Low pH (4.6) coupled with the high levels of exchangeable Al (5.88 cmolc kg-1), Al saturation of the ECEC (63%), and solution Al (2.20 mg L-1) in the Kokee soil did not affect PFP dry matter yield (DMY) compared to the other soil type X pH combinations. In contrast, at pH 4.6 the only medic to survive following clipping was M37 in Honolua soil where exchangeable Al, Al saturation percentage, and solution Al were much lower (1.21 cmolc kg-1, 26%, and 0.29 mg L-1). Kokee soil at pH 4.6 increased PFP neutral detergent fiber (NDF, total cell wall) concentration through an increase in hemicellulose, and thereby slightly reduced in vitro digestible organic matter (IVDOM) concentration. Barrel medic is unlikely to be a viable forage in Hawaii’s pasture systems due to its slow establishment and mediocre regrowth following defoliation in the humid subtropical environment. Legumes need to be vigorous producers like PFP in order to have a chance to persist and become an important component in Hawaii’s tropical C4 grass-based pasture systems. Keyword: Forage, perennial peanut, barrel medic, acid soils