Influence of topography and soil characteristics on Acacia senegal
A study was conducted to investigate the effects of soil characteristics, topography, sites and seasons on the distribution of A. senegal and on gum arabic production. Relationship between the gum yield and shrub morphological parameters were also investigated. Two sites, on the plain and on the hill slope, were selected for the study. One of the site on the plain and on the slope had no Acacia senegal. While one site with A. senegal were also selected both on the hill slope and on the plain. soils were sampled from profile pits and analysed for texture, moisture retention, hydraulic conductivity, pH, and fertility. Gum yield was measured by tapping randomly selected shrubs of A. senegal. Factorial layout was used in analyses of data on gum yield variation with the seasons, and sites. simple analysis of variance (ANOVA) was used in the analyses of soil parameters. Multiple regression analysis were used to select the parameters that best predicted gum yield. In the study area A. senegal predominantly occurred on the sandy sedimentary plains and rocky hill slopes of the old Precambrian gneissic Ndoto Mountain ranges. From the recorded data the factors responsible for the distribution of A. senegal on the hill slopes were inconclusive. At the plain sites a number of soil characteristics including texture, percentage of clay content, moisture retention and hydraulic capacities, and sodicity and salinity may have influenced distribution of A. senegal. Gum yield by A. senegal shrubs varied significantly with site (P<0.05) and seasons (P<O.OOl). The plain sites consistently yielded more gum than the hill slope sites. Highest gum yield was recorded for the shrubs tapped on the onset of 'the dry season (in early June), followed by the mid-dry season and least in the wet season. The average yield per shrub on the plain site was 118.21g for eight week harvest. On the hill slope over the same period the mean yield per plant was 13.13g per shrub. The was no conclusive explanation to what factor (s) were responsible for the discrepancies in the gum yield between the two sites. The observed morphological dissimilarities may have played a role. Multiple regression analyses indicated that height was the parameter which best predicted gum yield. Regarding phenological rhythms, optimum gum production was associated with average leaf cover of 50%, at least at the plain site. Potential commercial gum arabic exploitation in the study area is constrained by lack of infrastructure, low prices, and the low yield due to dependence on the natural exudation. Introduction of tapping practice may improve both the yield and quality of gum arabic and ensure sustainable utilization if other problems constraining gum arabic trade are addressed.