Influence of Simulated Defoliation and N Fertilization on Compensatory Growth of Gmelina arborea Seedlings

To investigate the effect of artificial defoliation and N availability on growth of Gmelina arborea, seedlings were subjected to three artificial defoliation levels (0, 25, 50%) and four N regimes (unfertilized, 1 g N plant-1, 3 g N plant-1, 6 g N plant-1) in a field trial. The results showed that height increment was 24.09% lower in the 50% defoliation than the undefoliated and 25% defoliation treatments which were not significantly different from each other. On average, the 25% and 50% defoliation treatments reduced stem volume increment by 44.34%. Increments of diameter and biomass and leaf production were not reduced by defoliation. In terms of response to N, increments in height and stem volume rose from 8.98 cm and 8.23 mm at unfertilized  to 11.39 cm and 12.13 mm at 3 g N plant-1, respectively, while number of new leaves increased by a margin of 1.51 from unfertilized to  6 g N plant-1. Total biomass increment that was unaffected by defoliation showed an increasing trend from 0.55 g at unfertilized and 1 g N to 0.83 g at 3 g N and 0.94 g at 6 g N plant-1. There was no significant interactive effect of treatments on any parameter, suggesting that the adverse effect of defoliation on growth of G. arborea seedlings may not be alleviated by N fertilization. It is encouraged that a similar study be conducted for a longer duration to ascertain if the responses are sustained or modified.