I have just entered a consultancy to investigate the use of legumes as an inter row planting in a large timber plantation. Currently the operation uses a combination of cultivation and chemicals to manage the vegetation between the rows.
This can be an expensive exercise over a large scale to continually manage the weed growth in order for the trees to rapidly develop. If the trees develop well the canopy will have developed to the extent where management of the inter rows becomes less intensive as the shading increases.
I am incorporating stylosanthes guianensis and crotalaria juncea (Sunn hemp) into a trial site to determine the effects of these two legumes with regards to reduce management and reduces expenses for the plantation. Stylosantes guianensis is a perennial which, if planted densely, should have the effect of crowding out weed competition, fixation of nitrogen and maintenance of cover to preserve moisture in the soil coming into the dry season. Stylo should also stay green through the dry season if it manages to get its roots deeper into the soil profile. These theories will be tested in the coming months.
Ctotalaria juncea on the other hand is an annual species though. The premise in this trial is that the sunn hemp, if planted densely, will also compete with the weeds. It can grow high and quickly which is good for the competitive aspects and then can be slashed at the onset of the dry season to create a thick mulch. Hopefully this will form a weed barrier and due to the dry conditions will slow the speed of decomposition of the mulch barrier. If left to go to seed before slashing it should have a large seed bank from which to recover with the eventual onset of the early wet season.
The key concepts are:
- Maintenance of cover
- Building of organic matter in the soil
- Maintenance of soil moisture
- N fixation for the benefit of the trees
- Competition with less desirable vegetation in the inter rows