Ethiopian Soils Research Articles

Optimisation of pressurised liquid extraction for the determination of p,p′-DDT and p,p′-DDE in aged contaminated Ethiopian soils

The effectiveness of extracting p,p'-DDT and p,p'-DDE from aged contaminated soil samples by means of pressurized liquid extraction (PLE) was evaluated. Two soil samples, which were contaminated more than 10 years ago, were used in the investigation. The static extraction time was optimised and then validated against the total sum of target analytes obtained from multiple sequential extractions. The PLE results were also compared with Soxhlet extraction (SOX). PLE for 3x10 min at 100 degrees C was proven to be more exhaustive than SOX in the determination of p,p'-DDE from both soil samples. In the case of p,p'-DDT, PLE was found to be equally as exhaustive as SOX. Additionally, most of the previous PLE investigations used hazardous organic solvents such as n-hexane, toluene and dichloromethane mixed with acetone, whereas in this investigation the less toxic solvent combination n-heptane/acetone has been employed.

Development of a pressurized liquid extraction and clean-up procedure for the determination of α-endosulfan, β-endosulfan and endosulfan sulfate in aged contaminated Ethiopian soils

Pressurized liquid extraction (PLE) was investigated for the extraction of two endosulfan isomers and their metabolite from two real contaminated soil samples. PLE for 3 × 10 min at 100 °C was proven to be more exhaustive than Soxhlet extraction (SOX) in one soil sample. On the other soil sample investigated the method was found to be equally exhaustive as SOX. The use of hazardous organic solvents such as n-hexane, toluene, and diethyl ether has been avoided in PLE and clean-up. Instead less toxic solvents have been used both at the extraction step (acetone/ n-heptane) and clean-up step (ethyl acetate/ n-heptane). A column Florisil clean-up procedure that consumes relatively low solvent volumes has been optimized and applied to purify soil extracts. The developed analytical procedure was validated by applying it to a certified reference soil material (CRM811-050). A recovery of 103% total endosulfan residue was obtained versus certified values.

Changes of humic substances characteristics from forested to cultivated soils in Ethiopia

The dynamics of the stable fractions of soil organic matter (SOM), the humic substances, has been rarely studied in tropical soils. We evaluated extraction yields, elemental composition, isotopic δ 13C abundance and solid-state 13C NMR spectra of humic fractions isolated from five forested and cultivated soils in Ethiopia in order to assess the influence of deforestation and subsequent cultivation on the composition of humic fractions. In all locations, humic (HA) and fulvic (FA) acids, humin (HU) and a humic hydrophobic fraction extracted with an acetone–HCl solution (HE) were decreased as a result of deforestation and cultivation, but the magnitude of decrease was site-specific. While the elemental composition of HA, FA and HU did not vary significantly with land use, that of the hydrophobic HE generally decreased with deforestation. Cultivation varied the δ 13C values of humic fractions with location and their high values suggested a history of C4 plants incorporation in soil. The 13C NMR spectra of HA, FA and HU showed that hydrophobic components (HB) were generally lower than hydrophilic ones (HI), resulting in a degree of hydrophobicity (HB/HI) being < 1.00. On average, cultivation decreased the HB/HI values of these humic fractions in all soils except for the Andisol. The HE material was much richer in hydrophobic groups showing a HB/HI ranging from 1.48 to 3.44 in the forested sites, but cultivation substantially reduced HB/HI ratios also for HE. Our data suggest that deforestation and progressive cultivation in tropical conditions decreased the content of soil humic substances and that the resulting humic pool was poorer in alkyl components and less hydrophobic than in forested conditions.

Metabolic and Genomic Diversity of Rhizobia Isolated from Field Standing Native and Exotic Woody Legumes in Southern Ethiopia

Eighty-seven rhizobial strains isolated from root nodules of field standing native and exotic woody legumes in southern Ethiopia were characterized using the Biolog method and AFLP fingerprinting technique. Cluster analysis of the metabolic and genomic fingerprints revealed 18 and 25 groups, respectively, demonstrating considerable diversity in rhizobial population indigenous to Ethiopian soils. While 25 strains (29%) were linked to members of Agrobacterium, Bradyrhizobium, Mesorhizobium, Rhizobium or Sinorhizobium, the bulk of the strains formed several distinct groups in both methods and did not relate to reference species included in the study. In contrast to exotic species which formed symbiosis with strains of only one specific genomic group, indigenous host species nodulated by metabolically and genomically diverse groups. The results in this study support the view, that long-term association between the symbionts allows gradual differentiation and diversity in compatible rhizobial population resident in native soils. Lack of significant metabolic and genomic relatedness to the reference strains in our results suggested that test strains in our collection probably included 'unique' types, which belong to several yet undefined rhizobial species.

Rhizobia nodulating African Acacia spp. and Sesbania sesban trees in southern Ethiopian soils are metabolically and genomically diverse

The diversity of 110 rhizobial strains isolated from Acacia abyssinica, A. seyal, A. tortilis, Faidherbia albida, Sesbania sesban, Phaseolus vulgaris, and Vigna unguiculata grown in soils across diverse agro-ecological zones in southern Ethiopia was assessed using the Biolog™ system and amplified fragment length polymorphism (AFLP) fingerprinting technique. By cluster analysis of the metabolic and genomic fingerprints, the test strains were grouped into 13 Biolog and 11 AFLP clusters. Twenty-two strains in the Biolog method and 15 strains in the AFLP analysis were linked to eight and four reference species, respectively, out of the 28 included in the study. Most of the test strains (more than 80% of 110) were not related to any of the reference species by both methods. Forty-six test strains (42% of 110) were grouped into seven corresponding Biolog and AFLP clusters, suggesting that these groups represented the same strains, or in some cases clonal descendants of the same organisms. In contrast to the strains from S. sesban, isolates from Acacia spp. were represented in several Biolog and AFLP clusters indicating the promiscuous nature of the latter and widespread occurrence of compatible rhizobia in most of the soil sampling locations. The results showed that indigenous rhizobia nodulating native woody species in Ethiopian soils constituted metabolically and genomically diverse groups that are not linked to reference species.

PARTICIPATORY ON-FARM CONSERVATION TILLAGE TRIAL IN THE ETHIOPIAN HIGHLAND VERTISOLS: THE IMPACT OF POTASSIUM APPLICATION ON CROP YIELDS

The two years on-farm tillage research during the 1999 and 2000 cropping seasons in Ethiopian highland Vertisol area demonstrated the importance of adapting cultural practices into participatory trials. The minimum tillage package could be an effective intervention for soil conservation due to the early-vegetative cover of the soil. Based on farmers' application of ash on Vertisols at Chefe Donsa, the incorporation of 50 kg ha−1 of potassium sulphate (K2SO4) in the on-farm trial significantly increased grain and straw yields of wheat. The nitrogen levels in the grain and straw of wheat on plots given K2SO4 were higher than those without. The nitrogen level for both wheat grain and straw was even higher when grown on plots previously growing legumes that received K2SO4. This showed that the availability of extra potassium in these soils improved the extraction of nitrogen by the wheat crop, thus improving the grain yield. The findings indicate the need to reassess the traditionally-practised system of not applying potassium fertilizer to Ethiopian soils.

Ethiopian soils harbor natural populations of rhizobia that form symbioses with common bean ( Phaseolus vulgaris L.).

The diversity and taxonomic relationships of 83 bean-nodulating rhizobia indigenous to Ethiopian soils were characterized by PCR-RFLP of the internally transcribed spacer (ITS) region between the 16S and 23S rRNA genes, 16S rRNA gene sequence analysis, multilocus enzyme electrophoresis (MLEE), and amplified fragment-length polymorphism. The isolates fell into 13 distinct genotypes according to PCR-RFLP analysis of the ITS region. Based on MLEE, the majority of these genotypes (70%) was genetically related to the type strain of Rhizobium leguminosarum. However, from analysis of their 16S rRNA genes, the majority was placed with Rhizobium etli. Transfer and recombination of the 16S rRNA gene from presumptively introduced R. etli to local R. leguminosarum is a possible theory to explain these contrasting results. However, it seems unlikely that bean rhizobia originating from the Americas (or Europe) extensively colonized soils of Ethiopia because Rhizobium tropici, Rhizobium gallicum, and Rhizobium giardinii were not detected and only a single ineffective isolate of R. etli that originated from a remote location was identified. Therefore, Ethiopian R. leguminosarum may have acquired the determinants for nodulation of bean from a low number of introduced bean-nodulating rhizobia that either are poor competitors for nodulation of bean or that failed to survive in the Ethiopian environment. Furthermore, it may be concluded from the genetic data presented here that the evidence for separating R. leguminosarum and R. etli into two separate species is inconclusive.

Influence of the addition of organic residues on carbohydrate content and structural stability of some highland soils in Ethiopia

Abstract. When over exploited and coupled with climatic conditions, tropical soils are subject to increased erosion and a loss of soil organic matter. Countermeasures include the incorporation of organic materials such as crop and animal residues. We studied the effect of adding crop residues and manure to soil, at five sites in Ethiopia, on carbohydrate properties, aggregate stability and the C and N distribution within water‐stable aggregates. The effects of organic amendments varied between sites. The largest content of carbohydrates was obtained in the control treatment at Holeta, Ginchi (90 kg ha–1 mustard meal), Jimma (5 t ha–1 cow dung + 9 t ha–1 coffee husk), Awassa (forested soil), and Sirinka (soil alley‐cropped with Leuceanae). The aggregate stability of these soils was highly correlated with the OM content but not with carbohydrates. The smaller aggregates (&lt;1.00 mm) accumulated more carbohydrates than the larger (&gt;1.00 mm), thereby suggesting a protecting effect within the finer soil fractions. A protecting role played by humified OM components was also indicated by the C and N distribution as well as the C:N ratios which showed preferential accumulation in small rather than in large aggregates. The isotopic 13C‐OC values of carbohydrate extracts were generally low, suggesting that OM was from plants with C3 photosynthetic pathways. Soil treatments with maize alone or combined with coffee husks at Jimma decreased the δ13C‰ values slightly, revealing that maize contributed a share of the labile OM. Despite the improvement in the soil OM content, neither the carbohydrate content nor the aggregate stability were increased to the level of the forested sites, suggesting that the additions of crop residues and manure were not alone sufficient to restore the soil physical quality.

Influence of the addition of organic residues on carbohydrate content and structural stability of some highland soils in Ethiopia

Influence of the addition of organic residues on carbohydrate content and structural stability of some highland soils in Ethiopia

Comparison of extractants for the determination of available phosphorus, potassium, calcium, magnesium and sodium in some Ethiopian and German soils

Abstract A study was conducted with the purpose of comparing the efficiency of Mehlich 1, Mehlich 3, and calcium acetate lactate (CAL) extractants for the deter‐ mination of available phosphorus (P) and exchangeable cations [potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)] on 22 Ethiopian and 10 German agricultural soils. The Olsen and NH4OAc extractants were used as standards against which P and exchangeable cations values were compared. Results showed that, in general, highly significant correlations were found between all of the methods for available P and exchangeable cations determination on the Ethiopian soils. The highest correlation was, however, found with the Mehlich 3 extractant. On the ten soils from Germany, the Olsen method did not give significant cor‐ relation with the CAL method for P determination. The CAL and Mehlich 3 extrac‐ tants were also not good indicators of Na availability when compared with the NH4OAc method. It can be generalized that the Mehlich 3 is a suitable e...

Response of ensete (Ensete ventricosum W.) to mineral fertilizers in southwest Ethiopia

Ensete (Ensete ventricosum W. Cheesm.) is a root crop which stores starch in the root and in the lower part of the stem. It is grown in the southwest of Ethiopia and due to its drought resistance, it is of outstanding importance for the supply of food to the local population. Until now virtually nothing is known about the response of Ensete to fertilizer application. Field trials carried out on three representative soils in Ethiopia showed that Ensete biomass yields were increased significantly on all three soils by nitrogen and phosphorus application. Potassium had only marginal effect on biomass growth but favourably influenced starch production. Sulfate application had no major impact on growth and starch yield. The yield response was well related to the level of available nutrients in the soil, as determined by electroultrafiltration (EUF). Leaf analysis provided preliminary evidence that optimum levels of N, P, and K may be 3.8%, 0.3%, and 4.8%, respectively.

Screening forage and browse legumes germplasm to nutrient stresses: III. Tolerance of Sesbania to aluminum and low phosphorus in soils and nutrient solution

Abstract Sesbania, particularly Esnabia sesban species, grow naturally in many parts of Africa where they form natural browse. Productivity of Sesbania as animal feed is widely limited by soil acidity and low P. In this study, eighteen ILCA accessions of S. sesban and two of S. goetzei, all but two from Africa, were evaluated for tolerance to acidity and low P on two Ethiopian soils as well as their tolerance to Al and response to P in nutrient solutions. The treatments were 0 and 4000 mg CaCO3/kg (pH 4.8 and 5.6) in combination with 0 and 37.5 mg P/kg on a Soddo Nitosol. On the Chencha clay loam with 77% Al saturation, the pH values were 4.1 (unlimed) and 5.9 (limed) in combination with 0 and 25 mg P/kg on the unlimed soil plus 37.5 mg P/kg on the limed soil. Treatments applied to the nutrient solutions were 0, 3, and 6 ppm (0, 111, and 222 μM) Al in combination with 5 and 200 μM (155 and 6200 ppm) P as KH2PO4. On the Soddo soil, Sesbania responded primarily to P which increased average shoot growth by 1...

Screening forage and browse legumes germplasm to nutrient stress: II. Tolerance ofLablab purpureusL. to acidity and low phosphorus in two acid soils

Abstract Although lablab (Lablab purpureus L.) is grown in many parts of Africa relatively little investigation has been done on its adaptation to acid soils, which are generally low in available P. In the present study, lablab was evaluated for tolerance to acidity and low available P on two Ethiopian soils. The two soils were a Nitosol (Soddo soil) and a clay loam with 77% Al saturation (Chencha soil). The pH of the Soddo soil unlimed was 4.8 and 5.6 when limed and with 0 and 37.5 mg P/kg soil applied at each lime rate. The treatments on the Chencha soil were pH 4.1 and 5.9 with combinations 0 and 25 mg P/kg added. There were highly significant (P<0.01) differences between the mean shoot and root dry matter yields and the shoot/root ratios of the lablab accessions on the two soils as well as plant height on the Chencha soil. The mean shoot and root dry matter yields were increased by liming alone by 14 and 23%, while P application increased growth by 8 and 12%, respectively. Lime and P together suppress...

Evaluation of African annual clovers to moisture stress in two Ethiopian highland soils

Five annual clover species from Ethiopia and Kenya were evaluated in greenhouse studies for biomass production, water use efficiency, and total nitrogen (N) accumulation when grown under different moisture conditions. Two Ethiopian highland soils (Nitosol and Vertisol) were maintained under either high or low soil moisture conditions until maturity. The largest biomass yields and N accumulations occurred in the high moisture treatment on both soils. One species (Trifolium tembense) was superior to the other four in biomass production over all soil and moisture treatments. Two species (T. decorum and T. quartinianum) were intermediate in performance, and two species (T. rueppellianum and T. steudneri) demonstrated low productivity over treatments. The results imply that at least three of the clovers evaluated may be capable of substantial biomass production and N accumulation on two Ethiopian soils that are commonly found in the central African highlands. These clovers should be evaluated in field trials in Africa to determine their use as pasture legumes to support livestock production.

Isolation of Rhizobium leguminosarum (biovar trifolii ) Strains from Ethiopian Soils and Symbiotic Effectiveness on African Annual Clover Species

Strains of Rhizobium leguminosarum (biovar trifolii) isolated from two Ethiopian soils or obtained from a commercial source were evaluated for symbiotic effectiveness on five African annual clover species. Numerous Rhizobium trifolii strains that exhibited varying levels of symbiotic effectiveness were isolated from both soils (a nitosol and a vertisol), and it was possible to identify strains that were highly effective for each clover species. The soil isolates were, as a group, superior to the strains from the commercial source. Several R. trifolii strains were found to be effective on more than one clover species, and there appeared to be at least two and possibly three distinct cross-inoculation effectiveness groups.

Agronomic effectiveness of rock phosphate in an andept of Ethiopia

Abstract In a greenhouse experiment, the relative agronomic effectiveness of Togo and Egypt rock phosphate sources were compared with triple superphosphate on high fixing volcanic ash soil of Ethiopia using (Medicago sativa) lucerne as the indicator crop. The P applied ranged from 0 to 160 kg P/ha. In the first cutting, Togo and Egypt rocks were relatively most effective at 60 and 43 kg P/ha, respectively. At these rates, Egyptian rock phosphate was 92% as effective as triple superphosphate compared with 64% for the Togo rock phosphate. Residual values of TSP were also higher than those of the rocks.

Phosphorus status of some ethiopian soils

The capacity to sorb P varied among some Ethiopian soils. Volcanic ash soils sorbed the maximum P while Fluvisols and Regosols sorbed the least. Sorption of P was significantly correlated with exchangeable and extractable forms of Fe and Al as well as pH and organic matter. But is was not related to the clay content of the soils. The role of Al was more important than that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.

Sulphur Investigations in Some Ethiopian Soils

Sulphur Investigations in Some Ethiopian Soils

Exoemission of Ethiopian Soils and the Endemicity of Non-Filarial Elephantiasis

Non-filarial elephantiasis is an endemic disease in the bare-footed population of Ethiopia. The distribution of this condition is linked with that of local red clay soil. Recently, thermoluminescence has been successfully used to distinguish between endemic and non-endemic soils. Intrinsic lattice defects, frozen in during cooling of volcanic material, are considered to be responsible for characteristic thermoluminescence signals. However, the biological reactivity of the absorbed soil particles will depend upon their surface properties. Exoemission has therefore been studied in samples from both endemic (5 samples) and non-endemic (4 samples) areas. All samples from endemic areas, on first heating, demonstrate an emission peak at 75 oC. Post-irradiation storage of samples in a moist atmosphere tends to decrease emissivity while wetting irreversibly reduces the response to irradiation. In an hydrated biological environment, this surface reactivity may be linked to the pathogenicity of the soil particles.

Exoemission of Ethiopian Soils and the Endemicity of Non-Filarial Elephantiasis

Non-filarial elephantiasis is an endemic disease in the bare-footed population of Ethiopia. The distribution of this condition is linked with that of local red clay soil. Recently, thermoluminescence has been successfully used to distinguish between endemic and non-endemic soils. Intrinsic lattice defects, frozen in during cooling of volcanic material, are considered to be responsible for characteristic thermoluminescence signals. However, the biological reactivity of the absorbed soil particles will depend upon their surface properties. Exoemission has therefore been studied in samples from both endemic (5 samples) and non-endemic (4 samples) areas. All samples from endemic areas, on first heating, demonstrate an emission peak at 75 oC. Post-irradiation storage of samples in a moist atmosphere tends to decrease emissivity while wetting irreversibly reduces the response to irradiation. In an hydrated biological environment, this surface reactivity may be linked to the pathogenicity of the soil particles.