Gmelina arborea - annual crop interactions in contour hedgerow systems for smallholder farm forestry.

The comparative growth performance showed that Gmelina with lateral branch pruning had smaller stem diameter (7.38 cm) compared to unpruned trees (9.83 cm). No statistical difference was noted on tree height. Upland rice grown in the alleys with unpruned Gmelina in contour hedgerows was shorter, chlorotic, and did not set seed. Dry herbage yield of rice was significantly higher in the open field control (3.87 t/ha) than in the pruned (1.51 t/ha) and unpruned (0.78 t/ha) treatments. Lateral pruning of Gmelina hedgerows resulted in a three-fold increment in grain yield over that obtained in the unpruned treatment. On a field area basis, the control produced a significantly higher grain yield (1.44 t/ha) than the pruned (0.92 t/ha) and unpruned (0.21 t/ha) treatments. Upland rice yield with unpruned Gmelina hedgerows was reduced by 30% compared to the pruned Gmelina hedgerows with only 19% reduction. In general, the growth and yield performance of corn in the alleys with unpruned Gmelina in the contour hedgerow was extremely poor. Soil pH and extractable P increased after the experiment. No significant change in Al concentration was obtained after upland rice. However, the concentration of Al in the soil decreased considerably after the corn cropping. Soil moisture content was higher in unpruned Gmelina compared to the pruned treatment. The incident light radiation on rice in the unpruned Gmelina was reduced by more than 50% of that received in the pruned treatment. Stem diameter increment of Gmelina at the end of the study was lower in the pruned (0.33 cm) trees compared to the unpruned ones (0.68 cm) 20 months after establishment. The inoculation of Gmelina seedlings with VAM resulted to earlier establishment of the seedlings and produced trees which were taller than the uninoculated ones. Systems productivity analysis revealed that the net returns were highest in the unpruned agroforestry system and lowest pruned agroforestry system. Negative returns were noted in the annual monoculture because the plants exhibited poor growth. Thus, establishing Gmelina hedgerow in small holder farm would promote higher income than crop monoculture alone.