Manure soil amendment for Grevillea robusta seedlings in the Kenyan highlands

Grevillea robusta seedlings are of high demand in Kenyan agricultural landscapes especially in agroforestry systems, yet the ideal soil mixture is not identified. This experiment was to determine the ideal potting soil mixture for Grevillea species. A Complete Randomized Design (CRD) with 4 treatments replicated 3 times was employed. Four treatments were used; Forest soil, Agricultural soil, Forest soil + Manure and Agricultural soil + Manure. The experiment was done for 8 months in 2020 at Egerton University tree nursery. Data was collected on seedling survival, height, root and foliage variables. One-way ANOVA was performed on the measured variables using SAS statistical package while the means were separated using LSD at P< 0.05. Results showed that Agricultural soil + Manure was significantly higher (P<0.05) in all the shoot and foliage variables compared with Agricultural soil alone except for internode length. Besides, Agricultural soil + Manure showed similar growth performance with Forest soil alone. However, the former showed significantly higher leaf length (20.2 cm) compared with Forest soil + Manure (14 cm). Results showed that Forest soil and Agricultural soil + Manure had significantly higher (P<0.05) root biomass compared with Agricultural soil (2.77 g), while root collar diameter, root length and root to shoot ratio were similar. It is, therefore, recommended that tree nurseries located far from forests can use a potting soil mixture of Agricultural soil + manure in raising Grevillea seedlings since this gives similar growth performance with forest soil.