Determining Rate of Liming for Attaining Optimum Soil pH and Tolerable Aluminum Saturation Level for Producing Bread Wheat in Strongly Acidic Soil of Guto-Gida District, East Wollega Zone, Western Ethiopia

Background: Bread wheat (Triticum aestivum L.) is one of the major crops cultivated in western Ethiopia. However, the crop is sensitive to soil acidity, which significantly reduces its productivity. The optimum soil pH for wheat production ranges between 6.0 and 6.5. The tolerable level of exchangeable aluminum saturation for producing the crop is below 10%. On the other hand, there is paucity of information on the extent of soil acidity, critical soil pH values, soil fertility, nutrient availability, and aluminum toxicity levels in the soil of the study region for making decisions to produce bread wheat production in the region. Objective: To assess the pH of the soil and its level of exchangeable acidity to determine the actual lime rate required for optimizing the soil pH and reduce Al concentration in the soil to a level that is suitable for producing bread wheat sustainably in the study area. Materials and Methods: Lime was used as an experimental material. The treatments consisted of 15 rates of lime, namely, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14 t ha–1. Acidic soil having a pH value of 4.87 was dug out from the top 0–20 cm depth using stainless steel shovel and taken to the experimental site for pH calibration. The experiment was arranged in CRD and replicated four times per treatment. The incubation experiment of a soil-lime reaction was conducted in 2020 using clay pots for a period of 42 days. After incubation, the soil in all pots was allowed to dry under room temperature, ground, sieved, and made ready for laboratory analysis. Thus, soil pH, exch. acidity, exch. Al, soil OC, TN, available P, exch. bases (Ca, Mg and K) and DTPA extractable soil micronutrients (Fe, Mn, Zn and Cu) were analyzed following the laboratory procedures. Results: The study revealed that applied rates of lime significantly (P ≤ 0.0001) increased soil pH (r2 = 0.95), available P (r2 = 0.97), TN (r2 = 0.94), exchangeable Ca (r2 = 0.91), Mg (r2 = 0.98), K (r2 = 0.95) and effective CEC (r2 = 0.92) while it significantly (P ≤ 0.0001) decreased soil exchangeable acidity (r2 = 0.99), %Al concentration (r2 = 0.99), OC (r2 = 0.96) as well as DTPA extractable Mn (r2 = 0.98), Fe (r2 = 0.96), Zn (r2 = 0.98), and Cu (r2 = 0.91) of the incubated soil. The soil target pH and Al concentration values identified were 6.23 and 9.97%, respectively, attained at 8 t ha–1 lime. At this target pH value, compared to the control, the soil exchangeable acidity (cmol(+) kg soil–1), Al concentration (%) and OC (%) were decreased by 1.36, 17.66 and 0.08 units, respectively. Similarly, the DTPA extractable soil Mn, Fe, Zn, and Cu each in mg kg soil–1 also decreased by 19.25, 16.07, 0.33 and 0.6 units, respectively. On the other hand, soil available P (mg kg soil–1), TN (%), exchangeable basic cations, namely, Ca, Mg and K, and effective CEC each in cmol(+) kg soil–1 increased by 9.75, 0.05, 3.8, 1.07, 0.08 and 4.1 units, respectively. However, the exchangeable acidity method-based lime requirement estimation proposed 5.04 t ha–1 which raised the soil pH value from 4.87 to 5.41 while reducing the Al saturation from 27.73% to16.77% at which bread wheat yield is reduced by more than 10%. Conclusion: At the determined target pH value (6.23), attained at 8 t lime ha−1 by the incubation method, Al concentration dropped below the level that has no/less toxic effect for production of wheat, and the soil pH value was increased from 4.87 to 5. 41 by exchangeable acidity method. The results imply that field evaluation of this lime rate should be done to verify its suitability for enhancing productivity of wheat by increasing soil pH and reducing the Al saturation.