MSc

Coconut based production systems in the tropics often aim at improved
resource capture through incorporating several trees and field crops. However,
competition between the system components are probable when multipurpose trees
are systematically interplanted in the coconut plantations. Soil fertility regimes are
presumably important in determining the magnitude of below ground competitive
interactions. Hence a study was conducted to evaluate the influence of interplanted
multipurpose trees on coconut productivity along a soil fertility gradient, to assess
the performance of multipurpose trees and to determine the nature of below ground
interactions between coconut palms and multipurpose trees, at Vellanikkara since
1992. Treatments included combinations of cocounut with anyone of the three
multipurpose trees namely, Vateria indica, Ailanthus triphysa and Grevillea
robusta, following two planting geometries(randomised block design, replicated
thrice). A soil fertility gradient, was super-imposed with high, medium and low
fertility levels in 2000. 32p soil injection technique was employed to characterize
.
root interaction and logarithmic spiral trenching technique for evaluating root
distribution pattern.
Results show that coconut yield was not adversely affected by
multipurpose trees interplanting until the trees reached eight years of age. Vateria,
ailanthus and grevillea showed marked variations in their growth rates. Initially
vateria recorded higher height and radial growth albeit ailanthus registered higher
growth rates subsequently.


Isotopic studies reveal that 32p absorption by coconut palms was similar
in both sole and mixed cropping situations along the fertility gradient; probably
implying the non-interfering nature of multipurpose trees. 32p absorption by vateria
and ailanthus suggests that the absorption of radioactive phosphorus declined
linearly with increasing distance ie. 32p absorption by multipurpose trees also did
not affect the 32p uptake by coconut, suggesting that integrated land use systems
involving multipurpose trees and coconut are ideally suited for improved resource
capture and increased system productivity.
Excavation of multipurpose tree root systems showed that proximal
locations recorded higher rooting intensities and that the rooting intensities
decreased with increasing distance. Size of the trees showed discernible differences
in respect of spatial root distribution pattern. Large sized trees showed higher root
distribution compared to small and medium. The first 10cm soil layer recorded the
highest rooting intensities. Ailanthus roots were distributed upto a maximum
distance of 469 cm, vateria upto 163 cm and grevillea upto 227 cm. Implicit in this
is the species-dependent'variations in lateral root spread. In general, vateria and
ailanthus have a well developed and ramified root systems. Grevillea, however,
had a less spreading root systems. Selection of tree species with low root
competitiveness and/or trees with complementary root interactions is of strategic
importance in agroforestry.