Effect of growth media and fertilizer application on biomass allocation and survival of Uapaca kirkiana Müell Arg seedlings

Uapaca kirkiana Muell Arg is one of the few recognized African fruit trees earmarked for conservation and domestication in southern Africa. However, efforts to raise seedlings of this species have been frustrated by the slow growth and high seedling mortality. Therefore, the objective of this study was to assess the effect of potting mixture, soil and foliar fertilizer application on plant growth, biomass allocation and survival of U. kirkiana seedlings in the nursery. Growth in height and diameter was best in plants with root to shoot ratio of <1 or 2.5-4. Growth in height and diameter significantly differed (P<0.01) with treatment main effects and interactions. The best growth was recorded in the treatment combination consisting of unsterilized forest soil + soil and foliar application fertilizer. The probability of plant mortality was significantly higher (P<0.01) in the potting mixture where saw dust was added (mean 0.47) than in the mixture without saw dust (mean 0.12). Mortality was also significantly higher (P<0.05) in unsterilized soil (mean 0.30) than sterilized soil (mean 0.13). Potting mixtures amended with soil-applied fertilizer had lower probability of plant mortality compared to those without. Disease incidence and seedling survival were related to biomass allocation in a curvilinear manner. It is concluded that survival of U. kirkiana seedlings in the nursery is a function of disease incidence, plant growth and biomass allocation, which in turn are functions of the growth medium and nutrient availability.