Growth responses of three Brachiaria species to light intensity and nitrogen supply

Abstract

Biomass production, dry matter partitioning and nutrient accumulation of 3 Brachiaria species (B. brizantha, B. decumbens and B. dictyoneura) were investigated under 3 photon fl ux densities (100, 57 and 29%) and 2 levels of soil N availability (with and without N added). Plants were grown in a controlled greenhouse under shade cloths in pots containing a mixture (1:1) of fi eld soil and perlite. Measurements were carried out at the end of 2 growth periods: 34 days after planting (GP) and 41 days after cutting (RGP). Artifi cial shade reduced biomass production during both growth periods but the effect was greater during GP. Nitrogen availability played an increasing role only as the study progressed. A light intensity × N interaction was observed in B. brizantha and B. decumbens, but not in B. dictyoneura. Shading increased plant allometric ratios and leaf N concentration. At 57% sunlight, total plant biomass in B. brizantha and B. decumbens was similar to that at full light conditions, when no N was added to the soil. B. dictyoneura had the lowest potential to adjust to restricted light conditions. The implications of these results in terms of forage yield and quality, and persistence under defoliation are discussed.