Browsing by Author "Asomaning, S.K."
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Item Acidity and Aluminum Speciation in Biochar Amended Tropical Soils(Taylor & Francis Group, 2022) Eduah, J.O.; Nartey, E.K.; Abekoe, M.K.; Asomaning, S.K.; Essibu, J.K.; Henriksen, S.W.Soil acidification in the tropics has become a more pressing issue due to its associated aluminum (Al) phytotoxicity. The chemical reactive nature of biochar can alter Al speciation in soils. The study assessed the chemical properties and Al speciation in a Ultisol and an Oxisol amended with corn cob (CC) and rice husk (RH) biochars charred at 300, 450 and 650°C in an incubation study for 120 d. pH was determined periodically while organic carbon (OC), cation exchange capacity (CEC), exchangeable base cations, exchangeable acidity, and exchangeable Al3+ were measured at the end of the incubation period. Dissolved organic carbon (DOC) and pH were also determined in soil solution from each treatment. Throughout the incubation period CC and RH biochars significantly increased soil pH, with CC biochar showing a greater effect. Similar effects were also observed for OC, CEC, and exchangeable base cations (Ca2+, Mg2+ and K+). Soil exchangeable Al3+ and exchangeable acidity, soluble Al and Al3+ activity in soil solution decreased significantly upon biochar application; it was more significant at the 650°C. Biochars at 300–450°C exhibited a more notable increase in soil DOC. At pH ≤ 5.8, Al-DOC and free Al3+ dominated in soil solution while at pH > 5.8, Al species was mainly Al-OH ions (i.e. Al(OH)2+, Al(OH)2 +, Al(OH)3, and Al(OH)4−). Biochars at 300–450°C promoted the large formation of Al-DOC while Al-OH ions dominated in 650°C-biochar treatments. Biochar can be used to ameliorate Al phytotoxicity in tropical acid soils, particularly at 300–450°C.Item Phosphorus sorption capacity in relation to soil properties in profiles of sandy soils of the Keta sandspit in Ghana(West African Journal of Applied Ecology, 2018-01) Asomaning, S.K.; Abekoe, M.K.; Dowuona, G.N.N.The sandy soils of Anloga in the Volta region form part of the Keta basin. The soils are infertile and of low productivity but are intensively cultivated for vegetables such as shallot (Allium cepa). Farmers have augmented the fertility of the soils by adding cow dung and poultry manure for the past seventy years. To study the P dynamics in the soils, three profiles were dug on cultivated (F) and two on uncultivated (U) fields to study P accumulation and sorption after decades of cultivation. The results showed that total P content was 533 mg P kg-¹ at the depth of 50 cm and below in the F-profiles compared to 416 mg P kg-¹ of similar depth of the uncultivated soils, suggesting some movement of P from the surface soil into the subsoil. The maximum P sorption capacity of the U soils was low (92 6 mg kg-¹) but higher than those of the F soils (58.8 mg P kg-¹). Multiple regression analyses showed that pH and Ca were the two major determinants of P sorption in the soils. The degree of P saturation (DPS) of the surface soils of the cultivated soils was higher than the average critical value of 25% DPS of an arable land but in the lower depths of the cultivated soils, the DPS decreased tremendously below the critical level of 25% which meant that these depths were not saturated well enough to enhance leaching of P to the underground waters.Item Sustainable long-term intensive application of manure to sandy soils without phosphorus leaching: a case study from Ghana(Acta Agriculturae Scandinavica Section B: Soil and Plant Science, 2015-08) Asomaning, S.K.; Abekoe, M.K.; Dowuona, G.N.N.; Borggaard, O.K.; Kristensen, J.A.; Breuning-Madsen, H.Long-term application of manure to sandy soils to ensure high crop productivity may lead to phosphorus (P) leaching, which, in turn, may deteriorate the quality of recipient waters because of eutrophication. The risk of P leaching depends on contents of aluminum (Al) and iron (Fe) oxides that are strong P sorbents and of calcium (Ca) that can form sparingly soluble Ca–P compounds. While P sorption by Al and Fe oxides is limited, the formation of sparingly soluble Ca–P may theoretically continue as long as enough Ca is available, i.e. under such conditions long-term application of manure may be environmentally sustainable. This hypothesis has been tested on soils formed on beach sand at Keta, Ghana, which have been used since the 1930s for intensive cultivation based on manure application. Soil samples were collected from different depths down to 80 cm in profile pits on cultivated soils that received manure over 70 years and on uncultivated plots (controls). The samples were analyzed for texture, pH, total C and P and poorly ordered Al and Fe oxides as well as different P forms as assessed by the Hedley fractionation method. The results showed a fourfold P increase in the top 40 cm of the cultivated soils, whereas in the deepest soil layers the P contents in the cultivated and uncultivated soils were almost the same indicating very limited downward P transport despite long-term manure application. This was supported by comparable P concentrations in groundwater taken under cultivated and uncultivated sites. P fractionation showed that the cultivated top soils were dominated by sparingly soluble Ca–P compounds that accounted for about 70% of the P gain. Thus, the results suggest that intensive crop production under tropical semi-arid conditions may be environmentally sustainable when based on manure fertilization ensuring enough Ca supply and neutral to alkaline pH. © 2015 Taylor & Francis.