Determination of optimum nursery soil misture and pot size for Eucalyptus camaldulensis and acacia mearnsii at Bako

A potting experiment was conducted on Eucalyptus camaldulensis. Dehnh and Acacia mearnsii De Wild at Bako tree nursery. Four different soil mix ratios along with three pot sizes were compared on two promising tree species so as to determine optimum nursery soil condition for proper seedling growth. The experiment was laid out in split-split plot design with three replications-pot size (8 cm, 10 cm, and 12 cm) as main plot, tree species (E. camaldulensis, and A. mearnsii) as subplot and soil mix proportion by volume (3 part local soil: 2 part sand:1 part forest soil, 3 part local soil:1 1 part sand: 2 part forest soil, 3 part local soil: 2 part sand:1 part farm yard manure, and 3 part local soil: 1 part sand: 2 part farmyard manure) as sub-subplot. Results from the present study revealed that seedling performance was not considerably affected by difference in pot size, but significantly (P £ 0.01) affected by difference in soil mixture. As the main effect of pot size is not significant, it is therefore advisable to use smaller pots for raising seedlings at Bako for economic reasons. But since the interaction between pot size and tree species was significant (P £ 0.05) for survival rate, it is recommendable to use the 8 cm pot size for E. camaldulensis and the 10 cm pot size of A. mearnsii. There was a differential response of the tree species to the difference in nursery soil mixture; that is, a potting mixture with more farmyard manure was better for E. camaldulensis ( 3 part local soil: 1 part sand: 2 part farmyard manure) than for a. mearnsii, but with more sand for the latter than for the former (3 part local soil: 2 part sand: 1 part farmyard manure). this could be due to the biological nitrogen fixing capacity of A. mearnsii and hence its ability to compensate for N in soils with less farmyard manure. The fibrous root nature of A. mearnsii also might have necessitated the need for sandy growing media as opposed to E. camaldulensis with tap root system although this was the case under nursery environment, the effect might be different under field condition after out planting. Therefore, further study is also required under field conditions to evaluate the field performance of seedling raised under different nursery soil conditions.