Volume 39, 42-53

Tropical Grasslands (2005) Volume 39, 42–53

Growth, forage yield and light interception and use by stands of five Brachiaria species in a tropical environment

O. GUENNI¹, J.L. GIL² AND Y. GUEDEZ¹

¹Universidad Central de Venezuela (UCV), Facultad de Agronomía, Instituto de Botánica Agrícola, Maracay, Venezuela
²Instituto Nacional de Investigaciones Agrícolas (INIA), Centro Nacional de Investigaciones Agropecuarias (CENIAP), Maracay, Venezuela

Abstract

Light interception and use were studied in fertilised stands of 5 Brachiaria species: B. brizantha, B. decumbens, B. dictyoneura, B. humidicola and B. mutica over a regrowth period of 45 days during the wet season. Aerial dry matter (DM) accumulation, nutrient concentrations in the forage, photosynthetically active radiation (PAR) interception and light use efficiency (ε) for different plant components were measured on 6 occasions. Growth and forage yield were analysed in terms of biomass partitioning and its influence on absorbed PAR and ε. Final DM yields were similar among species (280–350 g/m²), despite wide variation (1.7–4.1) in the leaf area index (LAI). In general, N accumulation into aerial biomass was lower than theoretical values expected for a C₄ grass. Although ε for leaf production and consequently LAI in B. humidicola and B. mutica were low, ε for tiller production was high, thus compensating for the lower partitioning to assimilatory biomass. The pattern of biomass partitioning in B. brizantha, B. decumbens and B. dictyoneura favoured leaf DM resulting in a higher leaf:tiller ratio, LAI and ε for leaf biomass. Different partitioning coefficients resulted in similar PAR interception among species. It was concluded that similar final yields were achieved by different strategies of biomass partitioning and therefore conversion efficiencies. The calculated value of ε for total forage biomass fell within the range 1.3–1.7 g/MJ.