Tropical grass/legume pastures in Northern Rhodesia

Abstract

Three grass/legume pastures were evaluated under Northern Rhodesian conditions.A plot trial measured the herbage yields of Stylosanthes gracilis, velvet beans (Stizolobium deeringianum) and giant Rhodes grass (Chloris gayana) grown as pure stands, and in a mixed association with Rhodes grass. The herbage was harvested for 3 years, and the plots were then planted with a maize crop to test any residual effects.After the establishment year, the D.M. yields, and especially the C.P. yields of the legume and grass/legume treatments, were markedly superior to grass alone. The increased yield of the grass/legume mixtures was due to the net gain contributed by legume herbage. There was no evidence of an underground transference of N from the legume to the associated grass.Although there was no measurable treatment effect on soil N and C, the maize following the legume and grass/legume treatments had a higher leaf N level, and approximately double the yield, compared with the maize following the grass-alone treatments.There were no significant differences in cattle weight gains when Rhodes grass alone, Rhodes grass/Stylosanthes, Rhodes grass/velvet beans, and Rhodes grass/pigeon peas (Cajanus cajan) were utilized as hay and foggage in the dry season.Digestibility trials showed mature Rhodes grass hay to be a submaintenance feed, deficient in dietary protein. The addition of Stylosanthes raised the herbage digestible C.P. fourfold. The Rhodes grass/Stylosanthes hay was a maintenance feed.The N yield of the grass/legume mixtures, although low by temperate standards, was 2½ times the N yield of grass alone. The potential value of a tropical grass/legume pasture will depend on the efficiency of the legume to fix N.