Tropical Grasslands (2007) Volume 41, 269–276

Irradiance and defoliation effects in three species of the forage grass Brachiaria


1 Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela
2 Instituto de Botánica Agrícola, Facultad de Agronomía, Universidad Central de Venezuela, Maracay, Venezuela


The responses of B. brizantha, B. decumbens and B. dictyoneura to shade and defoliation were examined in a glasshouse study. These combined stresses imposed severe constraints to growth and biomass production in all grasses. Shade alone reduced biomass linearly by 60–75% as irradiance decreased from 100% to 40%. There was no compensatory regrowth in any species and defoliation further reduced biomass accumulation. All grasses showed increased leaf N concentration, specific leaf area and chlorophyll concentration and fluorescence under shading. Overall, B. decumbens was the most productive under all sets of conditions and appears the best suited of the species tested to silvopastoral cultivation under moderate shade. Further studies under field conditions, where water and nutrients could be limiting, are warranted before the results could be extrapolated to commercial conditions.

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