Published online by Cambridge University Press: 27 March 2009
The contribution of the legume Stylosanthes gracilis to the nitrogen economy of mixed swards was assessed under both cutting and grazing conditions. In a cutting experiment, carried out during two wet seasons, a S. gracilis/Chloris gayana sward gave the same yields of dry matter and crude protein as a C gayana sward receiving 75 lb N and 167 lb N/acre (84 kg, 187 kg/ha) respectively. Lower yields were obtained from mixed swards containing Centrosema pubescens and Desmodium scorpiurus.
In a grazing experiment the mean live-weight production from a S. gracilis/Digitariasmutsii sward was equivalent to that produced from a pure grass sward receiving only 13 lb N per acre (5·9 kg/ha), although greater beneficial effects of the legume were apparent under high stocking conditions. In both experiments the legume tended to become dominant after 2 years.
Herbage yields from a S. gracilis/C. gayana pasture were significantly increased by phosphorus and sulphur; S. gracilis was particularly responsive to these elements. Under lenient defoliation, nitrogen reduced the proportion of the legume in the mixed sward, although frequent defoliation reduced the harmful effect of the nitrogen.
The results are compared with other published data and are discussed in terms of ways in which the grass/legume balance can be altered by different management practices.