Abstract:

Tobacco (Nicoliana tabacun, I.) growing takes up soil nutrients at a much faster rate than many other crops, thus rapidly decreasing the fertility of the soil and consequently requiring regular inputs of chemical fertilizers. Tobacco crop is also prone to several diseases and insect pests especially in early stages and. therefore requiring pesticides application to ensure a good quality crop. However, the environmental impact of these requirements particularly on flora diversity is not well documented in Uganda. During the period of two growing seasons, weed prevalence in Kigorobya and Kitoba sub counties of Hoima district was studied using standard quadrat sampling method in plots managed under; (1) first tobacco after bush fallow. (2) two consecutive tobacco crops after bush fallow, and (3) three consecutive tobacco crops after bush fallow. A comparative study was made to elucidate whether similar patterns of change in the flora were evident under maize crops grown as active fallow after the various tobacco crops under similar agricultural regime. At the beginning of the experiment a survey of nearby bush fallow land was undertaken to act as control in assessing differences in vegetation dynamics. Tobacco production incorporating the use of agro-chemicals did not have adverse effects on cither diversity or prevalence of the common macro-flora. Most of the grass species failed to show any recovery by the third cropping cycle of tobacco and the maize fallow break after tobacco cultivation while the broad leafed weed species showed increase from bush fallow under tobacco cultivation. Prevalence scores of weeds species such as E. floribundns, E. hirta, G. parviflora, M. merculiasis, D. velutina and C. benghalensis remained unchanged under the maize fallow breaks. Total viable counts of bacteria, fungi and bean nodulating rhizobia were not significantly affected by tobacco growing or the subsequent maize fallow break.