Forage production and nitrogen nutrition in three grasses under coconut tree shades in the humid-tropics

Abstract

Reduction in forage production (FP) under trees in the humid tropics is well known, but information on how different levels of nitrogen (N) fertilizer influence FP under trees is meager. The present study reports effects of four N fertilizer levels (0, 60, 80 and 120 kg ha -1 N) on net soil N mineralization rate (NMR) and soil moisture (SM), FP, shoot biomass/root biomass ratio (SB/RB), N concentration in SB, N uptake and nitrogen use efficiency (NUE) of three grasses [guinea (Panicum maximum Jacq.), para (Brachiaria mutica (Forssk) Stapf) and hybrid-napier (Pennisetum purpureum Schumach.)] under three canopy positions [under canopy (UC, representing high shade), between canopy (BC, representing low shade) and open] of coconut trees (Cocos nucifera L.) in a coconut based silvopastoral system in the humid tropical climate of South Andaman Island of India. The study was performed for two annual cycles (2005-2006 and 2006-2007). The hypotheses tested were: (1) FP would decline under tree shades, both in N fertilized as well as no N fertilized conditions, when SM was not growth limiting in the open. However, amount of decline in the FP would depend on grass species and intensity of shades i.e., higher was the shade greater would be the decline; (2) N fertilizer would increase FP under tree shades, but the increase depended on grass species, intensity of shades and amount of N applied. Amount of N applied, however, would not annul the shades effects when SM was not growth limiting in the open. The study revealed that the tree reduced light 59% under UC and 32% under BC positions, but the N fertilizer levels increased NMR by 11-51% under UC and 3-44% under BC positions compared to the open. SM did not differ across the canopy positions. Under all situations, FP of all grasses declined under UC (47-78%) and BC (18-32%) positions compared to the open; the decline was greater in Hybrid-napier than Guinea and Para grasses. Forage production of all grasses increased with N fertilizer increments under all canopy positions reaching 32 t ha -1 dry matters for hybrid-napier at 120 kg ha -1 N in the open. Both guinea and para grasses outyielded hybrid-napier grass under UC but not under BC or in the open. N concentration in the forage (SB) also increased as N fertilizer level increased. These observations support our hypotheses and suggest that forage production under coconut palms can be increased by the application of N fertilizer with both guinea and para grasses being more productive than hybrid-napier grass under the high shade. Where light conditions are better, hybridnapier would produce more forage than the other species.

Plant morphology and herbage accumulation of signal grass with or without fertilization, under different light regimes

“…Literature indicated that shading above 40-50% can affect the production of most forage grasses (BARUCH & GUEnnI, 2007;PAnDEY et al, 2011), which was confirmed in this study by the lower herbage accumulation under shading treatments, compared to full sunlight. Although signalgrass presents morphophysiological adjustments as a strategy for shade tolerance (GUEnnI et al, 2008), such mechanisms have been unable to compensate for the reduction of radiation and to maintain pasture productivity under conditions of intense shading.…”

“…Improvement of soil nutrients through fertilization could increase herbage production in silvopastoral systems. However, under storey forages showed that lower light availability Lopes et al could affect the efficiency of pasture responses to fertilizers applications, which also depends on the availability of nutrients in the soil and in grass species (PACIULLO et al, 2011B;PAnDEY et al, 2011). Some results have suggested the possibility of increasing herbage production in shaded conditions through the use of moderate doses of fertilizers (PAnDEY et al, 2011).…”

Massa de forragem, composição morfológica e valor nutritivo de capim-braquiária submetido a níveis de sombreamento e fertilização

“…1). Pandey et al (2011) relataram respostas positivas de três gramíneas ao fertilizante aplicado até a dose de 120 kg.ha -1 .ano -1 . Entretanto, foi constato que a eficiência de resposta ao nutriente aplicado foi inversamente proporcional à percentagem de sombreamento imposta ao pasto.…”

“…Entretanto, foi constato que a eficiência de resposta ao nutriente aplicado foi inversamente proporcional à percentagem de sombreamento imposta ao pasto. A resposta positiva ao fertilizante em condições de sombra moderada corrobora estudos que demostraram benefícios da fertilização em ambientes com luminosidade moderadamente reduzida e com uso de doses moderadas de adubo (Pandey et al, 2011;Gomez et al, 2013). Na maioria dos casos, sombreamento acima de 50% da RFA reduz acentuadamente a produção de massa de forragem (Abraham et al, 2014) e a resposta do pasto ao adubo aplicado (Guenni et al, 2008;Pandey et al, 2011), tornando a prática da adubação questionável nesses casos.…”

“…O aumento de nutrientes no solo poderia beneficiar a produção e o valor nutritivo do pasto. Entretanto, a restrição de radiação em sistemas silvipastoris pode afetar a eficiência de resposta de plantas forrageiras ao fertilizante aplicado, o que depende da espécie forrageira, das condições climáticas e do nível de sombreamento imposto ao sobosque (Pandey et al, 2011;Gómez et al, 2013).…”