GROWTH OF ANNUAL AND PERENNIAL GRASSES IN A SAVANNA OF BOTSWANA UNDER EXPERIMENTAL CONDITIONS

Seedling growth of three annual grass species, Chloris virgata, Setaria vetticillata and Tragus berteronianus, and five perennial grass species, Cenchrus ciliaris, Enneapogon cenchroides, Eragrostis rigidior, Panicum maximum and Urochloa mosambicensis is very species-specific and not related to the life history. Absolute plant biomass of annual grasses tended to be higher than that of perennial species after 10 days of growth. Variation in caryopses size has an impact on seedling quality by enhancing leaf area and root length in seedlings derived from huge caryopses. C. virgata and T. berteronianus were very responsive to increased soil nutrients, without severely affecting the allocation pattern to reproductive organs. In the vegetative phase leaf weight ratio was similar in annual and perennial grasses, but strongly decreased in annuals during the reproductive phase. Growth parameters such as LAR, NAR and RGR were not related to the estimated high and low fodder value of the grasses. The size structure of experimental and field populations of most grass species was L-shaped (positive skewness) al time of fruiting, except that of Set ria verticillata which maintained a normal distribution throughout the life cycle.