Influence of Charcoal, Manure and Fertilizer Soil Amendment on Growth of Grevillea robusta Nursery Seedlings

Soil amendment is vital especially in tree nurseries that are located away from the forest areas. Grevillea robusta seedlings are high nutrient demanders. An experiment was set up for a period of 8 months in 2021 at Egerton University, Njoro, Kenya to determine the effect of soil amendment on the early growth of Grevillea nursery seedlings. The experimental design was a CRD with 12 treatments replicated 3 times. The soil amendments included; manure, charcoal and artificial fertilizer combined with agricultural soil as well as their other combinations while forest soil was used as a check. The pot size was 9 by 12 cm in width and length respectively. Routine weeding and watering was done during the experimental period. The data was analyzed using SAS statistical package and the significance differences between means were separated using LSD at P<0.05. The results showed that forest soil and agricultural soil gave significantly (P < 0.05) the highest survival (84 and 81%) respectively compared with charcoal + manure + fertilizer combination (37%) which was the least. On the other hand, Forest soil had significantly (P < 0.05) the highest height (14.6cm) compared to all the other variables. Similarly, forest soil showed the highest root collar diameter (4.5 mm) which was significantly different from all the other variables measured except agricultural soil alone, agricultural soil + manure + fertilizer and agricultural soil + charcoal + manure which were similar. On the other hand, charcoal alone showed the highest root: shoot ratio (3.2), as well as root biomass which were significantly (P < 0.05) higher compared with agricultural soil + manure and charcoal + fertilizer. In conclusion, forest soil was superior in supporting the growth of both shoot, foliage and root collar diameter of grevillea seedlings. On the other hand, charcoal showed higher root to shoot ratio as well as root biomass. Forest soil is therefore recommended to be used in raising Grevillea nursery seedlings in areas nearby the forest. However, for areas located far away from the forest, a mixture of agricultural soil + manure + fertilizer or charcoal is recommended. Further research is recommended on using the same soil mixtures on other tree species which are less demanding in nutrient uptake.