Effect of Soil Mixtures on Early Growth Performance of Grevillea robusta and Cupressus lusitanica Seedlings in the Highlands of Kenya

Seedling production nurseries have been receiving much attention because of increasing demand for seedlings. In sub-Saharan Africa studies have showed over 50% of smallholder seedlings planted were sourced in tree nurseries. This has caused a rise in need to improve quality of seedlings especially focused on production level. The focus on most studies on early growth performance of selected key species important either for commercial plantation or agroforestry has been varied on length of the study periods and measurement parameters, with the focus never being to compare the farmer practices with the industry. This study main objective is to determine the effect of growing media on early growth performance of Grevillea robusta and Cupressus lusitanica seedlings in the highlands of Kenya. These species from literature have shown abundance in terms of demand and availability in smallholder tree nurseries and received complaints on varied performance. The parameters under observation were height, branch numbers, leaf numbers and survival of the seedlings of these species over a six-month period. There were 13 treatments which included various soil mixtures as follows: Agricultural soil (A), Forest soil (FS), Farmyard Manure (FYM), and Sand (S) and their combinations. The study employed a Completely Randomized Design with total of 390 seedlings per species. The performance showed that the soil mixture with the combined mean cumulative highest survival was FS 78±3.2% and combined mean lowest cumulative survival was A+S+FYM (37±4.2%). Cupressus lusitanica performed better in survival (70±1.2%), height (171±8.1mm), branch numbers (25±1.1), and leaf numbers (119±12.1), when compared to Grevillea robusta survival (38±1.6%), height (57±4.0mm), branch numbers (2±0.2), and leaf numbers (13±1.1%) in the nursery. Different soil mixtures had performed differently for each of the parameters in the study with key observation was FS+FYM+S was the best performing for C. lusitanica height, branching, leaf numbers and survival. The study also observed FS was best performing for the survival of G. robusta in the nursery. This study demonstrates that seedlings in the nursery for these two species require different soil mixtures to ensure survival and high growth performance.