Evaluation of Indigenous Grass Species Suitability for Rehabilitation of Degraded Semi-arid Rangeland in Suswa, Kenya

Abstract

Increasing soil erosion in Africa’s arid and semi-arid rangelands calls for requisite measures to reverse the trend. Although physical soil and water conservation (SWC) structures are effective in controlling soil erosion, they are capital intensive and therefore often not affordable to a majority of local communities. Pastoral communities require cheaper, labour effective and use of locally available materials that are adapted for rehabilitation of degraded land. In response, grasses with good rooting ability and adapted to the local climatic conditions could be one of the cost-effective measures to rehabilitate the degraded lands. The study aimed at evaluating the efficacy of different range grasses to reduce soil erosion as well as provide fodder for livestock. The study objectives were to 1) find out the grass species suitable for rehabilitation of degraded land from the community perspective; 2) evaluate the efficacy of the selected grasses for erosion control and, 3) determine the morphometric characteristics and above ground biomass yields of the preferred grasses. Using household survey, focus group discussions (FGDs), key informant interviews (KIIs) and direct observation, grasses suitable for rehabilitation of degraded lands were selected by the community. Cynodon plectostachyus (76%), Chloris gayana (73%), Pennisetum clandestinum (69%), Cymbopogon citratus (46%) and Themeda triandra (42%) were perceived as suitable for rehabilitation of the degraded rangelands. Fodder provision by the grasses came primary to soil conservation. A completely randomised design (CRD) experiment with three replications was conducted to determine the potential of C. plectostachyus, C. citratus, C. gayana, Cenchrus ciliaris, Enteropogon macrostachyus and Eragrostis superba for soil erosion control. Simulated rainfall of 116 mm hr-1 intensity was used to determine runoff and sediment yield from soil blocks xi measuring 25cm x 25 cm x 30 cm under simulation experiment. After erosion simulation, the soils were washed off the selected grass species to get the belowground biomass. Percolation, sediment yield and runoff were significantly (p≤0.05) influenced by grass species. Sediment yields varied between 1.01t ha-1 and 27.50 t ha-1 among the grasses species, while sediment detachment rate (SDR) decreased with maturity of the grasses. The root biomass was significantly (p≤0.05) different among the treatments with the control (naturally regenerated areas) having the highest (8.22 kg m-3) among the treatments, and C. gayana the lightest (0.455 kg m-3) among the grass species. The average root diameter of the treatments was 0.6059 mm. Cynodon plectostachyus had the longest fine roots of <1 mm in diameter (1119cm), while E. superba had the shortest (646cm). Cynodon plectostachyus had the highest root density (0.3924 km m-3), while E. macrostachyus had the lowest (0.0677 km m_3). Aboveground biomass production was relatively low but significant (P≤0.05) in all the treatments as compared to other studies that have been done. Cynodon plectostachyus had the highest biomass yield (0.9 t ha-1) while E. superba had the lowest (0.424 t ha-1). Plant height measured from the base of the plant to the tip of the leaf of the primary shoot varied amongst the grass species with the tallest being C. plectosachyus with 36.6 cm and the least being E. superba with 2.47 cm. The number of tillers and leaves per tiller increased with the maturity of the grasses. Cynodon plectostachyus, C. ciliaris and E. macrostachyus produced more tillers than the other four grass species. This study found positive significant correlation between the biomass yield and the morphometric characteristics. The results of the study show that communities’ indigenous knowledge on species suitable for rehabilitation and for fodder provision is very precise and important as community perceptions and priority differ with locality and their needs. Cynodon plectostachyus, C. citratus, C. ciliaris

and C. gayana were identified as the most effective for controlling erosion as well as most productive for livestock feed. Owing to the different perceptions, priorities and need for different communities, this study recommends a site-specific choice of grass species for rehabilitation with the guidance of local community if reversing land degradation and improving the livelihoods of the people is to be achieved. Decision-making is guided by the challenges affecting the local communities’ livelihood. Although the results of this study give indications of the potential of the various grass species in controlling soil erosion, a longer study with different ecotypes of the grasses is required to monitor the efficacy of the identified indigenous grasses in combating range degradation.