Can I grow Gmelina arborea on field bunds and boundaries instead of a full block?

Yes, boundary and bund planting is a good low risk way to grow Gmelina arborea without giving up your cropland. Planting along field bunds, boundaries and channel edges lets you keep growing your normal crops while the trees add a timber income at harvest, and it uses otherwise idle edge space. Keep the trees in a single line with enough gap so they do not heavily shade the field crop, and prune them to a clean straight bole for better timber value. Gamhar does best where there is enough moisture, so bunds near water or in higher rainfall areas suit it well. This approach spreads your risk, since your main income still comes from the field crop and the trees are a bonus. Confirm spacing and planting material with a local forestry nursery.