Leaf growth and senescence in Urochloa mosambicensis and U. oligotricha in a seasonally dry tropical environment

Abstract

Rates of leaf appearance, expansion and senescence were followed in swards of Urochloa mosambicensis (cv. Nixon, CPI 46876 and CPI 47167) and U. oligotricha (CPI 45607, CPI 47122 and CPI 47124) growing near Townsville, northern Queensland over a 3-year period. Rates of leaf appearance and expansion were greater for U. mosambicensis than U, oligotricha, but there were no differences between accessions within species. Rates of leaf appearance were high (c. 2 leaves tiller-1 week-1) at the start of the growing season and then declined. The weekly changes in rate of leaf appearance were closely related to changes in a water index (ratio of estimated evapotranspiration to potential evapotranspiration). Leaves of U. oligotricha commenced to senesce before those of U. mosambicensis, but their subsequent rate of decline was slower and so there was overlap between species for length of leaf life. Senescence was most rapid under favourable growing conditions and was more closely correlated with moisture supply than with temperature. The nitrogen concentration of green leaves declined substantially before there was any death, but the green portion of leaves always had a higher nitrogen concentration than the dead portion of a similar age.