New aboveground biomass and nitrogen yield in different ages of gliricidia (Gliricidia sepium Jacq.) trees under different pruning intensities in moist semi-deciduous forest zone of Ghana

Abstract

Pruning of woody perennials is extensively practiced among farmers in agroforestry. We investigated different pruning frequencies on new aboveground biomass, nitrogen concentration and nitrogen yield on gliricidia (Gliricidia sepium) trees of different ages. Two sites were selected in Ghana where gliricidia trees were intercropped in cocoa agroforestry system. One site had young (within 5 years) trees whilst the other had old (above 10 years) trees. A total of 15 gliricidia trees were selected from each site. Five pruning regimes (2, 4, 6, 8 and 10 months) was assigned to each tree and replicated 3 times. The result showed that shoot biomass among the different pruning regimes varied significantly (P < 0.05) in both age groups, with more biomass found in the shoot axes than in leaves as pruning delayed. Maximum biomass in old trees was 67.15 kg/tree at 8 months compared to 49.37 kg/tree at 10 months in young trees. N concentration pattern differed from the biomass, as %N were significantly lower (P < 0.05) as pruning delayed in both age groups. At 4 months, young trees had 57 kg N ha−1 compared to 64 kg N ha−1 at 8 months in old trees. In conclusion, pruning regimes in gliricidia should be guided by the age of the trees. Hence, it would be theoretically enough to prune young trees at 4 months and old trees at 8 months to meet the N need (58–80 kg ha−1) of cocoa to diminish external N-fertilizer needs.