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The Ethiopian Agricultural Research is one of the oldest and largest agricultural research system in Africa. Ethiopian Agricultural Research System (EARS) has evolved through several stages since its first initiation during the late 1940s, following the establishment of agricultural and technical schools at Ambo and Jimma. In 1955, a full-fledged agricultural experiment station was established at Debre Zeit (now named Debre Zeit Agricultural Research Center) under the then Imperial College of Agricultural and mechanical Arts (now called Haramay [...]




Kidanie Dessalegn Tarekegn(Researcher); Haramaya University [Corporate Author]

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A study was conducted at the Allaidege rangeland of zone three of Afar Regional State to assess rangeland degradation, its effect on soil depth on the soil seed bank flora and implication on carbon sequestration. Good, fair, poor and enclosed range sites were selected in order to assess parameters such as range condition scores, species richness, density, composition, diversity and evenness on both standing vegetation and soil seed bank flora (as necessary), while a fifth site (very poor) was latter added to study the effect of degradation on rangeland carbon sequestration as well as soil physical and chemical properties. Three levels of soil depth (0-3 cm, 3-6 cm and 6-9) were also set to examine the vertical distribution of seeds in the soil seed bank; while another three levels of soil depths (0-10 cm, 10-20 cm and 20-30 cm) were established to examine the vertical dynamics of soil physical and chemical properties. The data were analyzed in one-way (extent of degradation) and two-way (degradation and soil depth) ANOVA by using the SAS GLM. Sorensen similarity coefficient and t test were carried out to study the relationship between the two (standing vegetation and soil seed bank flora) communities. GC (Grass species composition), BC (Basal cover) and LC (Litter cover) were significantly higher in the good range site than in the poor one, while SEr (Soil erosion) and SC (Soil compaction) were the opposite. Overall species richness was significantly (p 0.
01) different among the range sites. The overall species density also significantly (p 0.01) varied from 6.24 plants m-2 in the poor range site, to 20.75 plants m-2 in the good range site. Species composition of perennial grass (PG) (5.10%) and desirable forb (DF) (2.02%) were significantly (p 0.01) lower in the poor range site, while that of annual grass (AG) (12.58%), less desirable forb (LDF) (72.76%) and undesirable forb (UDF) (7.14%) were higher. Both Shannon diversity index (H) and evenness (E) were significantly (p 0.01) higher (2.16 and 0.87, respectively) in the poor range site than in the good one (1.59 and 0.70, respectively). The overall species richness of the soil seed bank was significantly (p 0.01) higher (8.46) in the good range site with a nonsignificant difference among the other three extents of degradation. The overall species density of the seed bank was significantly (p 0.001) higher (859.97 seedling m-2) in the enclosed range site followed by the good one (548.10 seedling m-2); while in the fair and poor range sites, the density was lower and almost similar (277.58 and 325.99 seedling m-2, respectively). The good and enclosed sites had the highest (p 0.001) species density of PG, DF and LDF, while the poor site was highest only in the density of UDF. The good and poor range sites were not significantly (p 0.05) different in all of the species compositions except in UDF. The Shannon diversity index (H) was significantly higher (1.97) in the good range site than in the others. Nevertheless, species evenness (E) was higher (0.93) in the fair range site than in the others. All of the parameters except the species composition were significantly (p 0.001) higher in the shallower (0-3 cm) soil depth than in the others; and these parameters were significantly lower in the deeper (6-9 cm) soil depth than in the others. Apparently, the interaction effects of soil depth and xx degradation did not show significant (p 0.05) difference on any of the parameters except in the density of desirable forb species. According to the analysis of the relationship between the standing vegetation and the soil seed bank flora, the two communities were also significantly different in most species (PG, AG and DF) composition. Shannon diversity index (H) was not significantly (p 0.05) different between the two communities; however, species evenness was significantly higher in the soil seed bank (0.91 ±0.09) than in the standing vegetation (0.78 ±0.10). There was no significant difference (p 0.05) in soil physical properties among the range sites. A strong significant (p 0.001) difference in pH, EC, N, K and CEC was obtained among the range sites. The interaction effect of degradation and soil depth was not significant for most of the soil parameters. The good and enclosed sites had higher (2.03±0.26 and 1.93±0.41%, respectively) OC content in the 10-20 cm soil depth, while the fair, poor and very poor range sites had higher (2.10±0.22, 1.90±0.41 and 1.90±0.45, respectively) OC content in their shallower depth (0-10 cm). The average organic carbon density was about 2.04 g cm−3; and an average of 1.22 Gt carbon was sequestered in the top 30 cm of the rangeland. Generally, this study showed that species richness, density, diversity and evenness of rangeland soil seed bank flora can be altered by degradation, while species composition is more stable until disappearance of most species or colonization of new species occurs. As a result, seeds in the seed bank may assist restoration and rehabilitation of degraded range sites, unless the site is severely degraded. Furthermore, the study also reveals that the contribution of rangelands in carbon sequestration is so immense that they can be considered in climate change mitigation programmes.