MSc

A study carried out in the tree nursery of College of Forestry, Vellanikkara,
Thrissur to assess the autoallelopathic effect of selected multipurpose trees and the
effect of their leachate on agricultural test crop. The study on allelopathy is very
essential in agroforestry as it effect the yield and performance of the trees and crops
grown together and is essential to make judgment on the compatibility of trees and
crops. The allelopathic effect of different tree part leachates such as leaf leachate,
bark leachate and root leachate of selected trees viz., Acacia auriculiformis, Acacia
mangium, Ailanthus. triphysa, Grevillea robusta and Swietenia macrophylla on the
germination and growth of their own seedling and an agricultural test crop cowpea
(Var. Anaswara) were studied. The soil for the pot culture experiment was collected
from well established plantations of the MPTs and is used as potting mixture with
sand in equal proportion. The pots were irrigated with leachates of different tree parts
of these trees by soaking the tree part in water for 24 hours in 1:10 w/v concentration.
The monthly variation in nutrient status of the soil used for pot culture experiment
and the variation in the physicochemical properties of leachates at six intervals is also
estimated.
The effect of tree part leachates considerably varied among the germination
and biomass production in both allelopathic and autoallelopathic studies. The
observations on the germination per cent in allelopathic and autoallelopathic study
revealed greater inhibition in the pots treated with leaf leachate in all tree species,
except for S. macrophylla. With regard to biometric observations and biomass
production also, S. macrophylla performed as the best compared to other selected
species investigated for autoallelopathy. In case of the test crop also, it showed a
better growth in pots treated with the leachates from S. macrophylla.
The physicochemical analysis of the leachate of tree parts used to irrigate the
pots showed increasing trend in total solid, electrical conductivity, total phenol, total
carbohydrate and a decreasing trend in pH upto 36 hours. The physicochemical
analysis of leachates for total phenol showed a greater concentration in the leaves
than the bark and root.
Results converge to the generalisation that among the five selected tree
species the effect of auto allelopathy is negligible in case of S. macrophylla. The
better growth performance of the test crop in S. macrophylla tree part leachates shows
the compatibility of the test crop with the tree than the other selected tree species.