Volume 39, 75-87

Tropical Grasslands (2005) Volume 39, 75–87

Fertilisation of creeping signalgrass and bahiagrass under grazing in Florida

R.S. KALMBACHER, M.B. ADJEI, I.V. EZENWA AND F.G. MARTIN

University of Florida, Range Cattle Research and Education Centre, Ona, and Gainesville, USA

Abstract

Creeping signalgrass (Urochloa humidicola, syn. Brachiaria humidicola) is adapted to central and south Florida and shares many of the desirable characteristics of bahiagrass (Paspalum notatum), the main pasture grass in the state. Signalgrass has not been utilised in Florida and little is known about its management. Our first study (1997–98) was at Deseret ranch on land recently converted to pasture where 7 annual fertiliser treatments, using 56, 29 and 56 kg/ha N, P and K, respectively, were applied to signalgrass: 1) no fertiliser; 2) N in March; 3) N and P in March; 4) N and K in March; 5) N, P and K in March; 6) N in March & June (112 kg/ha N); and 7) N, P and K in March & June (112, 58, 112 kg/ha N, P and K). A second study was conducted at Ona (2000–01) with 7 treatments (1, 2, 5, 6 and 7 as above, plus N in June and N, P and K in June) applied to signalgrass and bahiagrass both recently sown on an area under pasture for 50 years. Signalgrass was unproductive in April–May, and there was little response to fertiliser. In April–June, yield of bahiagrass increased with N, but P and K had little effect. During July–October, signalgrass responded strongly to June-applied N with an additional increase in yield from P and K. Annual forage yields of both grasses were greatest in the NPK March & June treatment, which also resulted in the greatest annual uptake of N (232 kg/ha N). Recovery of N was greatest for signalgrass in the NPK June (168%) and N June (140%) treatments and averaged 93% and 73% for signalgrass and bahiagrass, respectively. Uptake of applied P and K differed between grasses with signalgrass having higher P and K concentrations, uptake and recovery in all treatments. Fertilisation of signalgrass should not be undertaken until May or June, whereas bahiagrass will respond to March-applied fertiliser. Both grasses will grow with low levels of P and K in the soil, but given P and K fertilisation, signalgrass contains greater concentrations of these elements in forage.