Variation in nutritive value of the grass species
The relative frequencies of the collected grass species across all sites are presented in Figure 1. Chrysopogon aucheri, Cenchrus ciliaris and Eragrotis papposa had high frequencies of >50%. Six other species were of intermediate frequency (20–25%), while the rest six grass species had frequencies below 20%. Overall, season, site and species type and their two and three-way interactions were significant (P<0.01) in terms of ash, CP, NDF and ADF contents. The results on chemical constituents are presented by site for each season in Table 1 to 4.
Relative frequency of herbaceous plants in the Borana rangelands of Ethiopia in the main rain season.
Species variation in crude protein (%) across different sites in the Borana rangelands during the main rain season
Variation of acid detergent fiber (%) between species and different sites in the Borana in the main rain season
There was some variation in crude protein content of the herbaceous species at Did-Tuyura, Dambala-Wachu and Surupha but this did not vary within site for the remaining sites (Table 1). Those species which showed relatively low CP content at Did-Tuyura site included: E. papposa, C. aucheri and Themeda triandra. Similarly, the CP recorded for Heteropogon contortus at Dambala-Wachu site was significantly (p<0.05) lower as compared to the CP of other grass species. Across sites and at species level only C. ciliaris, D. milanjiana, E. papposa and H. contortus showed a significant (p<0.05) variation in terms of CP (Table 1). Overall, the highest CP content was recorded in Bokkulboma as compared to the other sites. This was followed by values recorded for CP contents of samples from Did-Hara, Did-Tuyura, Mana-Soda, Surupha and Medhacho. We recorded a significantly (p<0.05) lowest average CP content at Dambala-Wachu. Within site, the ash content of grass species in the main rain season was significantly (p<0.05) varied among the grass species at Mana-Soda, Bokkulboma, Did-Hara, Surupha, Dambala-Wachu and Did-Tuyura. The grass species collected from Medhacho did not show variation in terms of ash content (Table 2). Across sites, the majority of the grass species exhibited significant (p<0.05) differences in their ash content. Themeda triandra, P. maximum and E. intermedia did not show any variation in terms of their ash content across the different sites. On average, the ash content recorded at Did-Hara was the highest (16.7%), while the lowest ash contents were recorded at Surupha (12.8%) and Did-Tuyura (12.5%).
Variation of ash content (%) among herbaceous species and across different sites in the Borana in the main rain season
Generally, the NDF content during the main rain season for the sampled herbaceous species was high >70% (Table 3). There was a significant variation between sites in terms of NDF with the highest value at Did-Tuyura (76.8%), while the lowest values were recorded at Medhacho (71.7) and Bokkulboma (71%). Within site, the NDF content was generally significant among the different grass species with the exception of Mana-Soda site. The ranking of individual grass species within sites was also greatly differed. There were a few species that had NDF values below 70%. These included: S. verticillata (65%) at Medhacho; S. verticillata (67.2%) and D. aegyptium (67.2%) at Bokkulboma and E. papposa (63.1%) at Surupha. Overall, across the study sites, the NDF content of T. triandra, A. adoensis, P.mezianum, D. aegyptium, S. verticillata and E. intermedia did not show any significant variations, while the remaining grass species exhibited significant variations across sites.
Variation of neutral detergent fiber (%) between species and different sites in the Borana in the main rain season
The average ADF content across the study sites was 46.5% and there was significant (p<0.05) site and within site variation in ADF content of samples (Table 4). Nevertheless, herbaceous species such as C. aucheri, T. triandra, D. aegyptium, S. verticillata and P. mezianum did not demonstrate variation across sites. At Medhacho, the ADF content showed no significant variation among species type. There were significant (p<0.05) differences in terms of RFV among the grass species except at Mana-Soda (Table 5). Only C. aucheri, P. maximum, D. aegyptium and S. verticillata did not show significant (p>0.05) differences in terms of the RFV of common grasses across the study sites.
Variation of relative feed value for herbaceous species across the different sites
Ranking of species by pastoralists compared to chemical analysis
The ranking of the common grass species by Borana pastoralists is presented in Table 6. Cenchrus ciliaris, C. aucheri, D. milanjiana, E. papposa and P. maximum were ranked as the top five grass species in the region. Digitaria naghellensis, C. dactylon, D. aegyptium, S. verticillata, P. mezianum and A. adoensis were perceived as species of low preference and palatability. The remaining grass species were considered as moderately valuable/palatable species (Table 6).
Rank of herbaceous species according to Borana pastoralists’ interest
The correlation coefficients between the perception ranking and the chemical constituents of the common grass species are presented in Table 7. The ranking of individual grass species for CP and ash content based on our respondents’ perceptions was positively correlated with the laboratory-based analysis of the same species both in the main rain and cold dry seasons. The structural constituents of NDF and ADF were negatively correlated with perception-based respondents’ ranking in both seasons. Generally, the laboratory-based analysis confirmed pastoralists’ experience and knowledge of forage quality and species preferences by a particular class of livestock. It seems that integration of these two sources of information can complement each other in future development endeavors.
Correlation coefficient between experience based herbage value rank and chemical composition determined by laboratory analyses
Seasonal effect on the nutritive value of herbaceous species
Annual rainfalls variability on the study sites are presented in Figure 2. Based on the nearest weather station at Yabello, Did-Tuyura, Did-Hara and Surupha had a better rainfall than the other study sites. Accordingly, Moyale is the nearest weather station for Bokkulboma, which had a better rainfall than Mega station (Dambala-Wachu, Medhacho and Mana-Soda). The mean monthly rainfall ranged from 8 to 150 mm at Yabello area, 6.7 to 128.2 mm at Mega area, 5.3 to 144.6 mm for Bokkulboma. The rainfall peaks are illustrating the bimodal nature of rainfall in the Borana. The main rain season was between March and May with the peak in April, and the short rain season was between September and November with the peak in October.
Annual rainfalls for year 2010 in the Borana region, Ethiopia.
Figure 3 presents the seasonal fluctuation of the quality of the common grass species in the study sites. There was a general decline in CP content from the main rain season towards the cold dry season. Generally, the highest CP content was recorded at Bokkulboma during the main rain season. The structural constituents (i.e., NDF, ADF) of the common grass species showed a slight increase during the cool dry season. The highest value for NDF was recorded during the cold dry season at Did-Tuyura and Mana-Soda. The lowest NDF value was recorded at Bokkulboma in both seasons. The ADF and ash contents of the herbaceous species did not show significant (p>0.05) differences between the two seasons.
Seasonal and spatial variability of chemical constituents of herbaceous plants in the Borana rangelands.
Physical and chemical properties of soil
The textural and chemical properties of soils from the Borana rangelands were significantly different (p<0.05) across the various sites (Table 8). Surupha soils had the highest proportion of sand and the least was recorded at Did-Hara. The silt texture was significantly high (p<0.05) in soils at Medhacho and least at Surupha. Clay content was highest in soils from Dida-Hara and lowest at Mana-Soda area. The soils in the area were generally alkaline with a mean pH value of 7. Mana-Soda and Medhacho had the highest pH values of 8; Surupha and Did-Hara recorded the lowest with values of 5.99 and 6.30, respectively. These pH values were corroborated by the base metal levels in respective soils. In general, there were variations in the soil chemical constituents across the sites.
Physical and chemical properties of soil at the different sites
The correlation coefficients between the chemical constituents of the herbaceous plants and soil properties are presented in Table 9. The CP content of the common grass species was negatively correlated with the proportion of sandy soils and Na+ in the studied soils (Table 9). On the other hand, there was a weak positive correlation between CP, silt, clay and the rest of soil nutrients. A negative correlation between the ash content of herbaceous plants and proportion of sandy soils was also observed. The ADF content of the herbaceous plants was positively correlated with the proportion of clay in the soil. The lignin content of the plants was positively correlated with the Na+ content in the study area. Furthermore, the ADL was positively correlated with the proportion of sandy soils, and negatively associated with silt and clay soils. The NDF content was negatively correlated with clay content in the soil but also positively associated with the proportion of sandy and silt soils.
Correlation between chemical constituents of herbaceous plants and soil properties in Borana, southern Ethiopia
Heteropogon contortus is a tropical, perennial tussock grass with a native distribution encompassing Southern Africa, southern Asia, Northern Australia, Oceania, and southwestern North America. The species has also become a naturalised weed in tropical and subtropical regions in the Americas and East Asia. The plant grows to 1.5 metres (4.9 ft) in height and is favoured in most environments by frequent burning. The plants develop characteristic dark seeds with a single long awn at one end and a sharp spike at the other. The awn becomes twisted when dry and straightens when moistened, and in combination with the spike is capable of drilling the seed into the soil.
The species is known by many common names, including black speargrass, tanglehead, steekgras (in Afrikaans) and pili (in Hawaiian). H. contortus is a valuable pasture species across much of its range however it has also been responsible for the elimination of the wool industry over much of Australia due to the seeds becoming embedded in the wool and skin of sheep and devaluing the wool and killing the animals. H. contortus seeds are also responsible for similar injuries in dogs with thick undercoats, or becoming embedded in the socks and skin of hikers.
Native Hawaiians used pili to thatchhale (houses).
Single seed demonstrating long twisted awn
Ripe seedhead Form