Abstract:
The potential of tree spacing/arrangement to alleviate effects of interspecific competition
of hedgerow intercropping systems on productivity and response to pruning of Jatropha
curcas (Jatropha) was investigated using a Jatropha e Pennisetum clandestinum (kikuyu) silvopastoral
system at Ukulinga (KwaZulu Natal, South Africa). Treatments were differentiated
by presence/absence of kikuyu and arrangement/spacing of Jatropha trees (one, two
and three tree hedgerows on either side of the alley) and had the same tree density
(1110 ha 1). When high water availability and kikuyu dormancy coincided, tree growth
rates did not significantly differ across treatments. Trees of the treatment without interspecific
competition (tree-only) were the tallest. Even when rainfall was high, post-pruning
tree height growth rate was affected by belowground (BG) interspecific competition and
tree spacing/arrangement. Treatment with a single tree hedgerow between alleys had the
most frequent maximum stem growth rate and was the most efficient during limited water
availability. Its trees showed slow initial response to pruning due to a high tree-grass
interface, followed by compensatory growth when competition for water with grass was
low. Generally, length of tree-grass interfaces affected yield inversely especially as trees
matured toward their maximum-yield age (4e5 years). BG competition reduced tree yield
more than tree biomass, while tree spacing/arrangement did not affect tree harvest index.
Manipulation of tree arrangement/spacing without changing tree density had no consistent
effects on tree productivity.
