Epsilon Archive for Student Projects

Abstract

A study on the effects of soil substrate and nitrogen fertilizer on the growth rate and biomass production of Acacia senegal and A. sieberiana in North Eastern Uganda was conducted between February and June, 2012. The objectives of the study were to determine the effects of soil substrate and nitrogen fertilizers on the growth rate and biomass allocation below-ground and above-ground of A. senegal and A. sieberiana seedlings. A multi-factorial experiment design was set up for collecting the data to address the two objectives of this study. There was a significant effect (P≤0.05) of soil substrate and the species- soil interaction on growth rate between two acacia species. The mean relative leaf length of A. sieberiana (0.013 mm mm-1 d-1) in unfertilized (N0) soil A was higher compared to those in the soils treated with N fertilizer. Analysis of variance shows that while there was no significant effect (P≤0. 05) of species, soil substrate and species- soil interaction on the relative stem and leaf biomass growth, relative root biomass growth, and the root biomass allocation and stem and leaf biomass allocation at final harvest, there was a significant species effect (P≤0. 05) on leaf N concentration A. senegal seedlings had a higher stem and leaf biomass allocation (83%) in soil substrate A with N0 compared to the N treatments. A. sieberiana and A. senegal planted in the unfertilized soil B produced higher relative stem and leaf biomass growth (0.034 g g-1 d-1) compared to those treated with N fertilizer. A. senegal had a higher leaf N concentration (7.1%, 6.6%, and 6.3%) in soil B treated with N50, N100 and N150 mg / plant, respectively, compared to the N0 treatments. Analysis of Pearson correlation showed that there was no statistically significant effect (P≤0. 05) of the leaf N concentration on the growth traits of the two acacia species in all treatments. It can be concluded that unfertilised soil substrates (N0) supported higher growth rate of both A. senegal and A. sieberiana seedlings than fertilization with a pure ammonium nitrate solution lacking other nutrients important for growth. It is recommended that further investigations using a complete and a balanced nutrient solution with small quantities of N fertilizers less than the rates used in this study be carried out. Application of the N treatment produced less stems and leaves biomass allocation compared to N0 treatments. Therefore, N fertilizers may not be used to enhance biomass production of two acacia species at the age 2 months. Further research can be conducted on the effects of N fertilizer on two acacia species for a long period of experiment. The two soil substrates affected the growth traits of the two acacia species differently while that on biomass allocation in the same way. The leaf N concentration did not enhance the growth traits of the two acacia species.