Plant morphology and herbage accumulation of signal grass with or without fertilization, under different light regimes/Morfologia e acumulo de forragem de capim-braquiaria com ou sem fertilizacao, sob diferentes regimes de luz

The silvopastoral system has been suggested as an alternative to recover degraded pastures in tropical regions. However, trees reduce the light available for pastures, which may affect the growth and herbage accumulation. The objective of this study was to evaluate the morphogenesis, canopy structure and herbage accumulation of signal -grass (Brachiaria decumbens) subjected to three light regimes (0, 20 and 70% of natural shading) and two fertilization levels (presence or absence of nitrogen, phosphorus and potassium). Leaf and stem elongation rates increased under shading but did not vary with fertilization. The leaf appearance rate was greater under fertilizer treatment but was generally similar among light regimes. The tiller density was greater in full sun and lower in intense shading. Tiller density responded to fertilization under full sun and moderate shading. Herbage accumulation increased by 42% with fertilization under full sun, 12% under moderate shading and did not vary under intense shading. Results showed that even under fertilization the herbage accumulation was limited by reduced light. However, under moderate shade the fertilization was important to raise tiller population over the growth cycles. Key words: Brachiaria decumbens, morphogenesis, shading, silvopastoral system, tiller density. Os sistemas silvipastoris tem sido sugeridos como alternativa para recuperacao de pastagens em regioes tropicais. Entretanto, as arvores reduzem a disponibilidade de radiacao para o pasto, o que pode influenciar no crescimento e acumulo de forragem. O objetivo deste estudo foi avaliar a morfogenese, a estrutura do dossel e o acumulo de forragem de Brachiaria decumbens, submetida a tres regimes de luz (0, 20 e 70% de sombreamento natural) e dois niveis de fertilizacao (presenca ou ausencia de nitrogenio, fosforo e potassio). As taxas de alongamento de folhas e colmos aumentaram com o sombreamento, mas nao variaram com a fertilizacao. A taxa de aparecimento de folhas foi maior com a fertilizacao, mas, em geral, foi semelhante entre os niveis de sombra. A densidade de perfilhos foi maior no sol pleno e menor na sombra intensa. A densidade de perfilhos respondeu a fertilizacao sob sol pleno e sombra moderada. O acumulo de forragem aumentou 42% com a fertilizacao no sol pleno, 12% na sombra moderada e nao variou na sombra intensa. Os resultados mostraram que, mesmo com uso de fertilizacao, o acumulo de forragem foi limitado pela reducao de luz. Em condicoes d