The growth of Urochloa accessions in grazed swards with Stylosanthes near Townsville, north Queensland

Abstract

Six Urochloa accessions (U. mosambicensis cv. Nixon, CPI 46876, CPI 47 167 and U. oligotricha CPI45607, CPI47122, CPI 47 124) were grown with Stylosanthes hamata cv. Verano and S. scabra cv. Seca in individually fenced, fertilized swards near Townsville, Queensland, for 5 years. The swards were grazed by single steers for 2 days at 6-weekly intervals (equivalent to a stocking rate of 1 steedha). Two grazing regimes were used: grazing throughout the year (high grazing pressure); and grazing during the dry season only (low grazing pressure). There was good establishment of Verano but Seca and all Urochloa accessions established poorly. In subsequent years there were few U. oligotricha seedlings but there were substantial numbers of U. mosambicensis seedlings. Most seedlings died during their first year and in the final year of the study the number of perennial Urochloa plants ranged from 1 /m2 (CPI 47 122) to 1 7/m2 (CPI 46876). Yield and proportion of Urochloa were low during the first year but later increased for the U. mosambicensis accessions, particularly CPI 46876, which out-yielded all other accessions in the final 3 years. High yields of Urochloa were associated with low yields of Verano and annual grasses. High grazing pressure reduced the total pasture yield. Verano was always a major component, especially at high grazing pressure. The proportion of Seca increased from an initial low level but then declined again to a very low level. There was very little native perennial grass at high grazing pressure. The proportion of grass in the swards was highest at the start of the wet season and then declined; in contrast, the proportion of legume increased during the wet season. The value of Urochloa species in seasonally dry tropical areas and their management in pastures are discussed.