Abstract:
The potential of tree arrangement in
optimizing radiation and soil water distribution and
crop yield of hedgerow intercropping systems was
investigated using a Jatropha curcas–Pennisetum
clandestinum (kikuyu) system (Ukulinga, South
Africa). Treatments (1110 t ha-1) of Jatropha-only
(JO), single-row Jatropha and kikuyu (SR), and
double-row Jatropha and kikuyu (DR) were used.
Treatments had asymmetrical radiation distribution
across tree–crop (T–C) interfaces and different radiation
interception by trees (JO: 27 %, SR: 11 %, DR:
8 %). Soil water varied among treatments and was
asymmetrically distributed showing no consistent
trend towards trees. Evapotranspiration was higher
(p\0.05) in SR than DR (13–65 %) and JO
(16–37 %) for most part of the season. Estimated fine
tree roots distribution was symmetrical in DR but not
JO and SR. Total roots in SR were concentrated in the
top 0.2 m (91 %) and beneath tree row (30 %), and
varied inconsistently with distance from trees. Grass
yields increased farther from tree rows and were
higher in SR (8.7 t ha-1 in 2006–2007; 4.3 t ha-1 in 2007–2008) than DR (by \9 %). Radiation use
efficiency of kikuyu (0.14–0.44 g MJ-1) also
increased with distance from trees but irradiance
correlated with grass yields poorly (R2\0.32) despite
high rainfall and no nutrient limitation. Considering
total productivity and evapotranspiration, DR was
better tree arrangement than SR. Water availability
dictated T–C interactions and intercrop yield more
than radiation. It was possible to optimize radiation
and water distribution and intercrop growth by
manipulating tree arrangement without changing
density.
