Abstract:
Farmers' survey and two field experiments were carried out at Siaya and Nyabeda in
western Kenya to investigate the effect of crown and root pruning on tree growth.
soil water dynamics, maize and wood yields, when trees are boundary planting along
agricultural crops. The experiment carried out at Siaya included 4 years old trees of
Casuarina equisetifolia. Eucalyptus grandis, Grevillea robusta and Markhamia hitea
while the one carried out at Nyabeda involved 5 years old G. robusta. The following
parameters were assessed over 5 and 4 cropping seasons at Siaya and Nyabeda
respectively: tree growth, light interception, soil water dynamics, tree water uptake
and maize yield. Results from the Siaya survey showed that 74% of the farmers grow
M. hitea on their farms, which is an indigenous tree species in western Kenya.
Eighty-four percent of the respondents observed that crop yields that are close to the
trees were very low compared to crops that were far away from the trees. The result
from the experimental data showed that all the four tree species in the test at both
sites survived both heavy crown and root pruning without any mortality or reduced
growth. Tree species showed significant (P<0.001) variability in branch biomass
produced from crown pruning at Siaya site. Eucalyptus grandis had the highest
biomass (107.2 kg/tree) production at the time of first pruning while M. lutea had the
lowest (5.5 kg/tree). New branch sprouts of pruned trees continued to grow in both
length and diameter. Eucalyptus grandis had the highest growth in both new branch
length and basal diameter (10.49 m and 13.44 cm respectively) while M. lutea had
the least (5.39 m and 6.75 cm respectively). Soil water under crown and root pruned
trees were significantly (P<0.05) high compared to the unpruned (control) tree plots. Soil water content decreased by 25-35% under un-pruned (control) tree plots of all
species as compared to soil water content under crown and root pruned tree plots.
Transpiration of crown and crown plus root pruned C. equisetifolia and G. robusta
trees was reduced by 50% as compared to unpruned trees. Maize grain yield was
positively influenced by photosynthetically active radiation (PAR) under both C.
equisetifolia (R2 = 0.84) and E. grandis (R2 = 0.97) boundary trees. During the first 3
maize cropping seasons, maize crops adjacent to pruned trees produced significantly
(P<().01) higher yield (50-80%) compared to that growing adjacent to the unpruned
(control) trees. Based on maize yield production, crown only pruning is
recommended for M. lutea and E. grandis trees while crown plus root pruning is
recommended for C. equisetifolia trees. Root only pruning is recommended for G.
robusta trees. Trees of all species need to be re-pruned every 1-2 years.
