Type: dissertation
Abstract: In Ethiopia, agriculture is the main economic sector, employing over 85% of the population. However, meeting the needs of the rapidly growing population has been challenging because crop productivity has declined, primarily due to land degradation by natural and anthropogenic factors. Soil acidity is one of the major constraints affecting over 43% of the country’s arable land. Although liming, chemical fertilizer and compost application, and growing acid-tolerant crops have been used to manage soil acidity and crop productivity depletions, their effectiveness was limited by the limited availability and short-lived effect of lime, high fertilizer costs, the lengthy and labor-intensive composting, and further fertilizer-induced soil acidification. Biochar has emerged as an eco-friendly alternative soil amendment. However, in the Ethiopian highlands, the co-application of biochar derived from waste materials such as water hyacinth with organic and inorganic fertilizers for soil amendment, plant development, and waste management remains underexplored, despite biochar effects significantly varying with feedstocks, soil types, and application methods. Additionally, the effect of biochar on nutrient leaching remains debatable, emphasizing further research needs. Therefore, the main objective of this study was to examine the effects of water hyacinth biochar and its co-application with organic and inorganic fertilizers on soil acidity amelioration and soil/plant nutrient interaction in the acidic soil of the Ethiopian highland. Two incubation experiments (Chapters 2 and 3) and one pot experiment (Chapter 4) were conducted. In Chapter 2 (91-day incubation), the effects of water hyacinth biochar on soil resistance to acidification stress and soil nutrient dynamics were examined using nine treatments: control (soil only), 1% and 2% applications of biochar produced using a furnace (WHBf) and a grounding method (WHBg), lime (L), fertilizer (F), 2% WHBf combined with fertilizer (2WHBfF), and lime combined with fertilizer (LF). Soils, except the control, underwent simulated acidification with nitric acid on days 35 and 63. Soil samples were collected at different times of incubation and analyzed for pH, exchangeable acidity, exchangeable aluminum (Al3+), available nitrogen, and available phosphorus. In Chapter 3 (90-day incubation), the impact of integrating water hyacinth biochar with organic and synthetic phosphorus (P) sources on the transformation of soil P fractions was explored using the treatments: control, P fertilizer (F; 138 kg P2O5 ha–1), poultry manure (PM) at equivalent P rate, and pairwise combinations of lime, and 1% and 2% biochar (B) with F and PM (LF, LPM, 1BF, 1BPM, 2BF, and 2BPM, respectively). P fractions were analyzed for soils sampled on days 3, 30, and 90. In Chapter 4, the effects of co-applying water hyacinth biochar with organic and mineral fertilizers on soil physicochemical properties, nutrient leaching, and plant response were investigated using 11 treatments: control, mineral fertilizer at the recommended rate of nitrogen (N) for barley (F; 69 kg ha–1), LF, PM at 50% (50PM) and 100% (100PM) of the recommended rate of N, and biochar at 1% (1B) and 2% (2B) application rates factorially combined with F, 50PM, and 100PM (1BF, 1B50PM, 1B100PM, 2BF, 2B50PM, and 2B100PM, respectively). Lime, PM, and biochar were applied one month before planting. Half of the urea and all P fertilizer (46 kg P2O5 ha–1) were applied at planting, and the remaining urea was added 40 days later. The barley plants were cultivated for 75 days. All pots were leached with equal volumes of water two weeks before harvesting. Plant height, leaf length, leaf width, leaf area, leaf number, and biomass (fresh and dry) were measured. Soils were sampled before planting and after harvesting and analyzed for different physicochemical parameters. The results in Chapter 2 revealed that water hyacinth biochar overshadowed lime in increasing the soil resistance against acidification, with 2% biochar application significantly increasing soil pH by 0.72–0.86 units, while decreasing exchangeable acidity and exchangeable Al3+ by 58.4–63.0% and 81.5–88.0%, respectively. The 2WHBfF treatment increased soil pH by 0.71 and 0.90 units, while decreasing exchangeable acidity by 49.8% and 64.7%, exchangeable Al3+ by 84.4% and 90%, and acidic H+ production by 35.1% and 19.2% compared to the LF and F treatments, respectively. Additionally, biochar application markedly enhanced available P and N dynamics. Chapter 3 presents results indicating that the B–PM and B–F integrations outstripped PM and F alone and with lime, substantially increasing labile P fractions by 1180–1795% and calcium-associated P by 372–611%, while decreasing Al/Fe-bound P fractions by 35–60% and recalcitrant P by 18–20% compared to the control after incubation. Chapter 4 presents results demonstrating that the B–PM treatments outperformed the B–F counterparts, considerably increasing soil pH by 0.79–1.65 units, organic carbon by 50.8–122%, and available P by 205–507%, while markedly reducing exchangeable acidity by 80.6–97.9%. More importantly, the 2BF, 2B50PM, and 2B100PM treatments eliminated exchangeable Al3+. Additionally, the B–PM and B–F treatments decreased ammonium-N (NH4+–N) leaching by up to 99.2% and 97.8%, and nitrate-N (NO3-–N) leaching by up to 97.5% and 95.6%, respectively. Consequently, barley growth was significantly enhanced, with shoot dry biomass (as a ratio to the control) increased in the order: control (1.0) < 50PM (2.1) < F (3.5) < LF (3.8) < 100PM (3.9) < 1B50PM (4.8) < 1BF (5.6) < 1B100PM (6.2) < 2B50PM (6.8) < 2BF (7.5) < 2B100PM (8.5). Overall, the study concluded that integrating water hyacinth biochar with fertilizers, especially with organic fertilizers, is an effective approach for ameliorating soil acidity, reducing nutrient leaching, improving overall soil health, and enhancing soil/plant nutrient interactions, thereby minimizing reliance on costly chemical fertilizers and promoting sustainable agricultural production and effective waste management in Ethiopia and similar tropical regions.
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7162738637