Abstract: The occurrence of Compositae weed species in Cola nitida, Eleais guineensis and Theobroma cacao plantations in Ekiti State, Nigeria was examined. Results obtained revealed that the compositae weeds constituted 73, 89 and 75% of the total number of weeds individuals sampled in the Cola nitida, Eleais guineensis and Theobroma cacao plantations respectively. The germination test conducted on the soil samples obtained from the three plantations also confirmed the dominance of the compositae weeds, in terms of density, in the soil seed bank of the commercial plantations. The percent compositions of compositae in the three plantations were 77, 76 and 77%, respectively.
INTRODUCTION
Cantero et al. (2000) did stress the importance of phytosociological knowledge of species composition and diversity as well as their variation in space and time. Previous phytosociological studies by Kayode (1999 and 2000) had revealed that Ekiti State is extremely rich in weed species. Consequently Kayode (1999, 2003 and 2005) had in the recent times examined the diversity of compositae weeds in abandoned farmland, existing farmlands and the roadsides of the study area respectively.
The agrarian communities of the study area possessed lots of commercial plantations most especially plantations of Cola nitida (vent.) Schott and Endl., Eleais guineensis Jacq. and Theobroma cacao L. Thus, the present study aimed at providing the phytosociological information on the compositae weeds of the commercial plantations in the study area.
MATERIALS AND METHODS
Detail description of the study area has been provided by Kayode (1999 and 2002). The state was divided into three zones: Ekiti North, Ekiti South and Ekiti Central, based on the existing geopolitical classification. Two plantations, each of C. nitida, E. guineensis and T. cacao were selected in each zone. In each plantation, a 100x100 m study plot was demarcated at the onset of the rainy season in June 2005. In each plot, a 50x50 cm quadrat was tossed fifty times and the compositae weeds in each quadrat were observed, identified, recorded and ranked based on their frequency of occurrence.
Also at the onset of the dry season in November 2005, five topsoil samples were collected within 20 m from each other from each of the demarcated plot. In each sample, the soil and the litter were carefully removed from 1x1 m quadrat to a depth of 4 cm in clean sacks. Germination experiments were later carried out in an open field using 25x25x10 cm germination boxes. Each box was filled to a depth of 9 cm with flame sterilized potting soil. The samples were thinly spread (2-5 mm) over the soil for maximum light exposure. Five boxes were used for samples from each plot.
Germination boxes were arranged randomly and watering was done twice daily (at 7.00 and 18.00 h GMT). The emergence of compositae was monitored daily for 28 days and seedlings were removed as they germinated. The Index of Similarity (IS) in the occurrence of compositae weed species in the soil samples was determined according to Kayode (1999).
RESULTS AND DISCUSSION
Fifteen, seventeen and seventeen weed species were obtained from the C. nitida, E. guineensis and T. cacao plantations respectively. Among these species, the compositae constituted 53, 47 and 47, respectively. However, when the densities of the individual weed species were considered, the compositae constituted 73, 89 and 75% of the total number of weeds individuals in C. nitida, E. guineensis and T. cacao plantations respectively. This tends to suggest the dominance of the compositae species in these plantations (Table 1).
C. odorata, B. pilosa and S. nodiflora were the most dominant compositae species in terms of the abundance (Table 2). The indexes of similarity in the frequency of the compositae weeds in the three plantations were 87, 100 and 100%, respectively for C. nitida/E. guineensis, C. nitida/T. cacao and E. guineensis/T. cacao plantations (Table 3). Thus, indicating that the compositae weed species were common to all the three plantations. Kayode (1999) had earlier inferred that areas with similar climatic conditions will enhance the growth of related weed species. The test on the soil seed bank further confirmed the dominance of the three compositae i.e., C. odorata, B. pilosa and S. nodiflora and indeed members of the family compositae in the three plantations. The percent compositions of compositae in the three plantations were 77, 76 and 77%, respectively (Table 4). Compositae species germinated readily and profusely from the soil samples collected from the three plantations.
| Table 1: | Demographic features of weeds in commercial plantations of Ekiti State of Nigeria |
| Table 2: | Rank order of the occurrence of compositae weeds in commercial plantations of Ekiti State, Nigeria |
| Table 3: | The Index of Similarity (IS) in the occurrence of compositae weed species in the soil samples |
| Table 4: | Cumulative germination of weeds from the seed bank of soil samples from commercial plantations of Ekiti State, Nigeria |
The occurrence of the compositae weed species in the seed bank of the commercial plantations might be attributed to their mode of reproduction, which is mainly from seeds that are widely dispersed by wind. Most of these seeds, according to Numata et al. (1964) are later buried in the soil due to the continuous accumulation of litter in the plantations. Some of such seeds germinated readily, especially those that occurred in depths ranging between 1 and 3 cm (Etejere and Okoro, 1989), when exposed to favourable light conditions (Kayode, 2005).