Soil Science

Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/45

Browse

Now showing 1 - 5 of 5

THE DYNAMICS OF LAND USE MANAGEMENT ON CARBON SEQUESTRATION, SOIL PROPERTIES AND VEGETATION ATTRIBUTES IN BORANA, SOUTHERN ETHIOPIA
(Hawassa University College of Agriculture, 2018) KENEA FEYISA JIRATA
The Borana rangelands of southern Ethiopia have been extensively used as grazing lands by pastoralists for millennia.However, there has been a dramatic shift from prime grazingland to cultivation, left unused because of bush encroachment, and highly degraded leading to different land use/land cover types in the region. Therefore, this thesis work was designed to study the dynamics of land use management on carbon sequestration, soil properties and vegetation attributes by considering the roles played by enclosure management, different land use systems, the aboveground biomass of woody species, and long-term ban of prescribed range fire. This study was conducted in Yabello district of Borana, southern Ethiopia during the period from June-August 2013. A paired-site design approach was used in this study, where sampling plots (30 m x 30m each) with nested’ subplots for field data collection on soil and vegetation layers were establishedin a systematic random sampling techniquealomga 500 m long transect line in each adjacent experimental site.Using enclosures versus the adjacent open-grazed as control, our results showed that the SOC and TN contents and stocks increased in enclosures as compared to the adjacent open-grazed rangelands, although the differences were not significant (P > 0.05) and varied along the age sequence and soil depths.Overall, totalmean SOC stocks of 39.6 ± 3.5 Mg ha−1 in the younger (< 20 years old), 40.8 ± 3.4 Mg ha −1 in the medium (20–30 years old ) and and 51.0 ± 4.4 Mg ha −1 in older (> 30 years old) enclosures age categories, whereas in the adjacent open-grazed areas the values ranged from 34.4 ± 2.5 to 47.9 ± 5.1 Mg ha−1in 0-30 cm. The herbaceous biomass was significantly (P<0.05) higher inside enclosures (115.4 gm m-2) than that of the adjacent open-grazed rangeland areas (43.6 gm m -2).The study in this thesis showed that the Borana rangelands had undergone substantial changes in land use/land cover during the last 37 years. Our results also showed that mean SOC stocks (0-30 cm) in woodland was 55.94±3.41 Mg ha-1,while for enclosure, grazing xvii and cultivated lands the values were 50.03±3.03, 45.79±4.00 and 38.10±2.39 Mg ha -1 , respectively. Additionally, woodland had the highest (7.52±0.43 Mg ha-1), while cultivated land had the lowest (5.58±0.35 Mg ha-1) total nitrogen stock. The potential changes of SOC and TN stocks also showed both gain and loss based on the present measurements and historical land use change. The developed species specific and mixed species allometric equation models for majorities of the investigated woody species ithat related the total above-ground, stem and branches biomass components well fit to the measured dendrometric variablesas as indicated by their adjusted coefficient of determinations and highly significant (adj.R² > 0.80; P < 0.001). The study on long-term of ban of fire on carbon stocks in soil and woody biomass, and TN stock across the two landscape site showe that relatively higher SOC and TN contents and stocks as well as herbaceous biomass carbon in burned than unburned areas, whereas more accumulation of woody biomass carbon was recorded in the unburned sites (40 years of fire exclusion).Overall, this study will contribute to the existing knowledge gaps in terms of the potential of SOC and TN stocks related to different rangeland management practices as well as anestimate of the above-ground woody biomass in arid and semi-arid ecosystems of southern Ethiopia. However, it is suggested further study including other variables such as climatic factors, seasonality and inherent soil properties across wider landscapes, which may have confounding effects on the dynamics of carbon sequestration other than land management practices for the sustainable use of the savanna rangelands of southern Ethiopia.
ANALYSIS OF CLIMATE VARIABILITY AND CHANGE AND ITS IMPACTS ON WATER PRODUCTIVITY AND NUTRIENT USE EFFICIENCY OF MAIZE (Zea mays) IN THE GREAT ETHIOPIAN RIFT VALLEY BASINS
(Hawassa University College of Agriculture, 2021) FITIH ADEME MAMO
Climate variability and change are a global phenomenon affecting many nations. Smallholder farmers in Ethiopia have been facing severe climate related hazards, in particular highly variable rainfall and severe droughts that negatively affect their livelihoods. Anticipated climate change is expected to aggravate some of the existing challenges and impose new risks beyond the range of current experiences. This study aimed at understanding current climate variability and future climate change, and its associated impacts in particular for maize production. The climate analysis was conducted in the Great Rift Valley Basins (GRVB), which represents diverse agroecology and farming systems. The climate variability and change impact study were conducted in the Central part of the Rift Valley (CRV), which represent a major cereal-based farming system of the semi-arid environments of Ethiopia. Empirical statistical analyses using field experimental data in combination with crop-climate simulation modelling were used to achieve the objectives of the study. A high spatial resolution regional climate models and a well-known crop growth simulation model were used for the modelling analysis, which is an innovative feature of the methodology used in this thesis. The analysis revealed that rainfall exhibited high interseasonal variability (coefficient of variation 13-37%) during the period 1981-2010 in the GRVB. The mean annual temperature significantly increased by +0.43 ºC [0.27 ºC to 0.58 ºC] per decade in the same period. Projections for future climate suggested that annual rainfall will change by -25 to +6% and the annual temperature is expected to increase in the range of 2.5-5.1oC by the end of this century. A corresponding change in length of growing period (LGP) from -5.66 to -25.5% for central semiarid and +3.9 to -16.4% for central sub-humid highlands was simulated in the near century. Maize grain yield was strongly (P<0.01) and positively correlated with seasonal rainfall (r=0.67-0.69) in the CRV while day temperature affected grain yield negatively (r= -0.44) at Ziway (P<0.05) during the simulation period. Simulated water-limited yields showed high inter-annual variability (coefficient of variation, ~24%) and about 47% of this variability was explained by the xvii variation in growing season rainfall. The observed farmers’ yield was 28, 48 and 57% lower than the researcher-managed, water--limited and potential yield of the crop, respectively, indicating wide maize yield gap in the region. Analysis of climate change scenarios showed that maize yield will decrease on average by 16.5 and 23% by mid and end of this century, respectively due to climate change. Similarly, water productivity is expected to decline on average by 2.2 and 12% in the CRV by mid and end centuries with respect to the baseline. Nutrient uptake and corresponding nutrient use efficiency (NUE) might also be negatively affected by climate change. Phosphorus uptake probably will decrease in the CRV on average by 14.5 to 18% by mid-century. Nitrogen and P use efficiency indicators showed decreases in the range between 8.5 to 10.5% and between 9.3 to 10.5%, respectively by midcentury relative to the baseline average. The simulation under no water and nutrient limitation condition ensured improvements of both water and nutrient use efficiency in the changed climate which could ensure modest production in the future. The high estimated impact of climate variability and changes on crop yield and associated resources use in the CRV imply greater risks on rainfed crop production in the region. Hence, the study recommends further assessment of potential adaptation options and economic impact of climate related risks in the region to provide full-fledged evidence for better policy decisions.
SOIL CHARACTERIZATION, EFFECTS OF NITROGEN SOURCES, TILLAGE METHODS AND CROPPING SYSTEMS ON SOIL PROPERTIES AND MAIZE (Zea mays L.) IN THE CENTRAL RIFT VALLY OF ETHIOPIA
(Hawassa University College of Agriculture, 2022) ASHENAFI NIGUSSIE ADAFRE
Declining soil fertility is one of the major challenges to crop production and productivity in Ethiopia. Thus, addressing this challenge through developing new techniques and application of integrated soil management practices tailored to a particular crop and location is vital to improve crop productivity and production. Given this, studies were conducted in two districts of the central rift valley of Ethiopia with objectives: (1) To characterize and identify the soils of the study areas (2) To evaluate the effects of compost, inorganic nitrogen fertilizer and their mixture on soil properties, growth, and nitrogen uptake of maize, and (3) To assess the combined effects of tillage methods, cropping system and nitrogen fertilization on selected soil chemical properties, maize performance; and organic carbon and total nitrogen stocks. Two pedons, one from each, site were excavated and characterized with respect to morphological, physical and chemical properties. Pot trials were executed using a factorial combinations of five compost rates (0, 5, 10, 15, and 20 t ha-1 ) and four inorganic nitrogen fertilizer rates (0, 46, 92, and 138 kg N ha-1 ), laid out as a completely randomized design with three replications. Field study was carried out using three-factors arranged as split-split plot arrangement in randomized complete block design with three replications. The tillage methods were used as the main plot, cropping system as a subplot, and four levels of nitrogen fertilization as the sub-sub plot. Maize variety BH 546 was used as a test crop. The results of soil characterization showed great differences in their morphological, physical, and chemical properties within and among the profiles. Accordingly, the soil of the Dore Bafeno site was classified as Cambisol (Loamic, Aric, Humic), whereas, the Bati Dubano site was classified as Someric Phaeozems (Pantoclayic, Aric). The analysis of variance showed that the combined application of compost and inorganic N fertilizer significantly improved soil chemical properties, plant growth, and nitrogen uptake, compared to the unfertilized or separate addition of compost and/or inorganic N fertilizer. Similarly, different soil management practices were significantly affecting grain yield, N-uptake xxviii and selected soil chemical properties. In both soils, the conventional tillage and haricot beanmaize rotation system increased the yield and yield components, and N-uptake in contrast to the minimum and maize monocropping, respectively. However, tillage methods differed in their effects on soil organic carbon and total nitrogen stocks, which were improved through MT compared to CT. Therefore, a CT plus haricot bean-maize rotation system with the addition of sole inorganic N at 92 kg ha-1 and integrated 46 kg N ha-1 + 10 t compost ha-1 should be recommended, to achieve better yield and yield components as well as N-use efficiency, for Cambisols in Hawassa Zuria and Phaeozems in Meskan study sites, respectively. Nevertheless, to ensure sustainable maize production in the studied soils, we recommended that the integrated application of 46 kg N ha-1 + 10 t ha-1 compost along with MT and legume-based crop rotation, which can enhance soil properties, and in the long run will improve yield, and N-uptake as well as utilization efficiency. This is because the field study was carried out only for two consecutive years and generated short-term results. Therefore, a longer-term study should be carried out at similar soils/sites to assess the long-term effects of tillage practices, cropping systems, and nitrogen fertilization on soil properties, and yield and yield components as well as nitrogen utilization efficiency
CHARACTERIZATION, MAPPING, AND EVALUATION OF RECLAMATION RESOURCES FOR SOILS AROUND ABAYA AND CHAMO LAKES, SOUTHERN ETHIOPIAN RIFT VALLEY
(Hawassa University College of Agriculture, 2024) AZMERA WALCHE MENGESHA
Characterizing and understanding the nature of the soil and its management are crucial for successful crop production. With this in mind, experiments were conducted to (1) characterize of soils surrounding Lakes Abaya and Chamo, (2) analyze nutrient contents and map the fertility status of agricultural soils, (3) determine the intensity and types of soils and map their spatial distribution patterns, and (4) investigate the efficacy of gypsum and farmyard manure and their combined application in reclaiming sodic soil's chemical and physical properties. The first study revealed that the soil properties in the study site were highly heterogeneous in terms of morphological, physical, and chemical characteristics. Most of the studied soils were highly alkaline (>8.5), had very high sodium content (>20 cmolc kg-1 ), very high CEC value (> 40 cmolc kg-1 ), very low TN (<0.1%), and low levels of organic carbon (0.5-1.5%) and exchangeable calcium (2-5 cmolc kg-1 ). The study recommended removing sodium and salts from the soil depth to improve the productivity of agricultural soils in the area. Applying organic amendments such as manures and crop residues was also suggested to increase fertility and organic matter content. The second study showed the soil texture in the area was mainly clay, heavy clay (Ganta Kanchama site), and sandy clay loam. The surface soil had a higher available water holding capacity than the subsurface depth, indicating more plant water storing space. The soils in the studied area had an alkaline pH, moderately (2-4 dSm-1 ) to highly saline (4-8 dSm-1 ) EC values, high exchangeable sodium percentage (50-70%), high soil CEC, low OC, very low total nitrogen content, high potassium availability (>300 mg kg-1 ), and xxiii lower calcium carbonate content. The study showed the soils of the area were fertile, however, incorporating organic matter into the soil enhances its structure, water retention, and nutrient availability, reducing salinity and sodicity. The results of the third experiment revealed that the study area has moderately (7.9-8.4) to strongly alkaline soil pH (8.5-9.0), slightly (0.75-2 dS m-1 ) to moderately saline (2-4 dS m-1 ) EC values, and a high variability in soil ESP values, indicating a strong variability in soil sodicity across different parts of the study area. Out of 2274.65 ha of the studied area, 62.28%, 26.09%, 10.99%, and 0.63% were categorized as nonsaline non-sodic, saline-sodic, sodic, and saline, respectively. The results showed that almost all salt-affected sites were situated in relatively low-lying slope (0-2 %) areas, flat to almost flat slopes. The findings suggest that the place needs specific soil management strategies to address the salinity and sodicity problems. The last study investigated the impact of amendment resources on sodic soils. A pot experiment consisting of a factorial combination of four levels of GYP (0, 50, 100, and 150%) and four levels of FYM (0, 10, 20, and 30 tons ha−1 ), with Complete Randomized Design (CRD and three replications was used. The results showed that applying gypsum (GYP) and farmyard manure (FYM) reduced exchangeable sodium percentage (ESP) in sodic soils. Specifically, using 10 ton FYM ha-1 and GYP at 100% GYP required (GR) rate resulted in a 99.8% decrease in ESP compared to untreated composite sodic soil. The study also indicated optimal amendment levels (combined application of 100% GYP and 10 ton FYM ha-1 ) for displacing exchangeable sodium from the exchange site using prediction models. Agglomerative hierarchical and K-means cluster analysis suggest that treatment levels and reclaimed soils with similar properties require application of comparable treatment levels and similar management. The study found that combined applications of GYP (at 100% gypsum requirement rate) and FYM (10 ton FYM ha-1 ) reduced ESP to less than 10% in agricultural soil. However, further research is needed to determine their effectiveness at the field level.
INTEGRATED USE OF DRY AZOLLA BIOMASS AND INORGANICNITROGEN FERTILIZER FOR SOIL AND TOMATO (Solanum Lycopersicon L.) PRODUCTIVITY IN SELECTED DISTRICTS OF SIDAMA REGION, ETHIOPIA
(Hawassa University College of Agriculture, 2025) HABTAMU ALEMAYEHU LOREBO
Declining soil fertility and insufficient fertilizer application can limit crop yield. Integrating Azolla used as a source of organic nitrogen, with inorganic nitrogen fertilizers presents a promising strategy to improve soil health and crop productivity in tropical agroecosystems. This study was initiated to characterize soil, evaluate the effects of integrated application of Azolla dry biomass and inorganic nitrogen fertilizer on soil nitrogen mineralization, yield and nitrogen use efficiency of tomato in Hawassa Zuria and Wondo Genet, Sidama Region. The research conducted included soil characterization, through greenhouse, field and laboratory experiments with four specific objectives: (i) to characterize and classify soils at experimental sites,(ii) to determine the influence of Azolla dry biomass and inorganic N-fertilizer applications on selected soil chemical properties and as well as yield and yield components of tomatoes under greenhouse conditions,(iii) to evaluate the integrated effects of Azolla dry biomass and inorganic nitrogen fertilizer on soil chemical properties, nitrogen use efficiency, growth and yield of tomatoes, and (iv)determine the effects of Azolla dry biomass on soil nitrogen mineralization under controlled conditions. The first experiment, aimed to characterize and classify soils at experimental sites. A representative pedon was opened at each site to a depth of 2 x 2 x 2 m, and the profiles were described using the Guidelines for Field Soil Descriptions (FAO, 2006). A total of 12 disturbed and 12 undisturbed soil samples were collected from each diagnostic horizon at Jara Gelalicha, Hawassa Zuria and at Aruma, Wondo Genet locations. The soil analysis results showed that the surface horizon textural class of the pedon of Jara Gelalicha is sandy loam, whereas the textural class of the pedon at Aruma is sandy clay loam. Based on the World Reference Base for Soil Resources (WRB), the soils of the study areas were classified as Eutric Cambisols (Loamic) in the Jara Gelalicha area and Eutric Andosols (Loamic) in the Aruma area. Generally, the sitespecific soil characterization and classifications could offer crucial information for designing soil management options to increase soil productivity. The second experiment, aimed to determine the influence of Azolla dry biomass and inorganic nitrogen fertilizer on soil chemical properties, yield and yield components of tomato under greenhouse. The treatments included four levels of Azolla dry biomass (control (0), 25, 50, and 75 g pot⁻¹) and four levels of inorganic N 2 fertilizers (0 (non-fertilized), 0.23, 0.46, and 0.69 g pot⁻¹). The pot experiments were set up using factorial combinations within a completely randomized design (CRD) with three replications. In a greenhouse pot experiment, the interaction between Azolla dry biomass and inorganic nitrogen had a significant impact on various plant characteristics. The best results were achieved with the combined application of 75 g Azolla pot-1 and 0.69 g pot-1 of N, resulting in the highest marketable fruit yields at the Hawassa Zuria and Wondo Genet locations, which were 1088.43 g/plant and 833.73 g/plant, respectively. Field research is required to confirm the greenhouse findings and provide appropriate recommendations. Therefore, a third experiment, aiming to evaluate the integrated use of Azolla dry biomass and inorganic N fertilizers on soil chemical properties, growth and yield components, and nitrogen uptake and nitrogen use efficiency of tomato production was conducted under field conditions. Two-year field experiments were conducted in the Hawassa Zuria and Wondo Genet districts of the Sidama region. The experiment took place over two years in (2022/23 and 2023/24), a factorial combination of four rates of dry Azolla biomass (0, 5, 10, and 15 t ha⁻¹) as an organic nitrogen source and four rates of inorganic N fertilizer (0, 46, 92, and 138 kg N ha⁻¹) was evaluated. The treatments were arranged in a randomized complete block design (RCBD) with three replications. The combined two-year data showed that the highest marketable fruit yields in the Hawassa and Wondo Genet locations were 23.76 t ha⁻¹ and 26.35 t ha⁻¹, respectively. This was achieved by adding 15 t ha⁻¹ of Azolla biomass and 138 kg ha⁻¹ of nitrogen. It is integrated application of 15 t ha-1 of Azolla and 138 kg N ha-1 is recommended for tomato production in both districts. The combined application of 15 t ha⁻¹ and 138 kg ha⁻¹ led to the highest fruit N uptake (1093.48 kg ha⁻¹ in Hawassa Zuria and 1486.94 kg ha⁻¹ in Wondo Genet, while the control treatment had the lowest. The final experiment was aimed to determine the effects of Azolla dry biomass rates on soil nitrogen mineralization under controlled conditions. In addition, an incubation experiment using a completely randomized design (CRD) with three replications was conducted to determine the combined application of four rates of Azolla dry biomass (0, 15, 30, and 45 g pot⁻¹) and eight incubation periods (0, 7, 14, 21, 28, 42, 49, and 56 days of incubation). The results showed that the highest nitrogen mineralization occurred after 42 days of incubation with 45 g kg⁻¹ of Azolla in soils from both locations. The highest total mineralized N was found after 42 days of incubation in Hawassa Zuria and Wondo Genet (39.88 and 48.57 mg kg⁻¹ soil, respectively). Field research is essential to confirm the laboratory findings and provide appropriate recommendations.