The effect of soil moisture on seed production, seed characteristics and short-term dynamics of Cenchrus Biflorus (roxb.) in arid rangelands of Western Sudan
This study deals with a phenomenon observed to occur in the arid rangelands of Western Sudan. During a sequence of seasons of relatively high or above average rainfall, a dominant annual grass species, namely Cenchrus biflorus (Roxb.), was noticed to decrease and almost disappear in some areas while other grass species such as Eragrostis termula (Steud) tend to increase and almost dominate. It was noticed that this phenomenon occurred even in places where C. biflorus was growing almost in a pure stand. Considering the apparently favourable soil moisture conditions prevailing the dynamics of decrease or disappearance of C. biflorus seemed to be abnormal. It has been reported that the dominance of some grass species and the decrease or disappearance of others during periods of favourable soil moisture conditions is mainly due to the competitive ability of the former species. This study approached the phenomenon from a different point of view assuming that ~ factor or factors other than just competition could be involved in this seemingly complex dynamism. The study focused on the effect of high soil moisture conditions experienced during a short rainy season on seed production and seed reproductive characteristics in C. biflorus. The study, further, investigated the effect of competition between C. biflorus and E. termula on seed production and seed reproductive characteristics in C. biflorus under different levels of soil moisture. xiv The study comprised a field experiment in which C. biflorus was grown under different levels of soil moisture in a pure stand as well as in combination with E. termula which was used as a competitor. Data collected included seedling mortality during the early stages of growth, days before flowering, seed numbers, seed weight, and seed viability in C. biflorus. Results obtained showed that C. biflorus seedlings had better chances to establish under conditions of high soil moisture than under conditions of low soil moisture. Competition on the other hand demonstrated significant effect on mortality rate but it could not eliminate C. biflorus seedlings under any of the soil moisture conditions used. At the flowering stage results showed that high soil moisture conditions prolonged the vegetative phase in C. biflorus resulting in delayed flowering. The study also demonstrated that under high soil moisture levels C. biflorus produced larger numbers of seeds but relatively lighter in weight than those produced under low soil moisture levels. Finally the viability of seeds produced was tested and the results showed that seeds of C. biflorus produced under conditions of high but limited soil moisture were less viable than those produced under conditions of low soil moisture.