Influence of potassium fertilization and liming on growth, grain yield, and quality of soybean (Glycine max L. (Merrill) on acidic soil in Gobu Sayo District, western Ethiopia

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The experiment was to evaluate the influence of potassium fertilization and liming on growth, grain yield, and quality of soybean (Glycine max L. (merrill) on acidic soil in Gobu Sayo district, western Ethiopia. Soil acidity problem is one of the bottlenecks to improve crop production in high rainfall areas of Ethiopia in general and in western parts of the country in particular. A field experiment was carried out during the 2016 main cropping season at three sites (Gishe, Laften and Ago). Five levels of potassium fertilizer (0, 20, 40, 60, and 80 kg ha-1) and two levels of lime (0 and 4.6 t ha-1) were applied as two factors. Fifty (50) kg ha-1 P2O5 with seed inoculation by biological organism (legume fix strain) was also used as standard check. The eleven treatment combinations were arranged in a randomized complete block design (RCBD) with three replications. KCL was used as K2O source and applied in two splits at planting time and at vegetative growth stage. The full dose of lime was broadcasted a month before planting on those plots which received lime. Soil samples were collected during pre-sowing and after harvesting to analyze for selected soil properties. The analysis of soil sample after harvest indicated that the soil pH was raised from very strongly acidic to slightly acidic level for Gishe and Laften sites and from strongly acidic to moderately acidic for Ago site. Furthermore, percent organic carbon and total nitrogen as well as exchangeable bases showed considerable increase after harvest for soil treated with lime at the rate of 4.6 t ha-1. The analysis of variance indicated that there were highly significant interactions (P<0.001) between potassium and liming for all measured plant variables, except for number of primary branches, tap root length and number of seeds per pod. The highest soybean grain yield (3642 kg ha-1) was obtained at Gishe site when 60 kg ha-1 K2O and 4.6 ton ha-1lime was applied while the lowest yield (1014 kg ha-1) was recorded at Ago site for the control treatment. The partial budget analysis also revealed that application of 60 kg ha-1 K2O with 4.6 t ha-1 lime has a substantial economic advantage on acidic soils of the study areas. Application of K2O significantly increased protein content of soybean seeds but lime and its interaction with K2O or K2O alone had negative effect in reducing oil content of soybean seeds. Hence, K2O at a rate of 60 kg ha-1 with 4.6 t ha-1 lime can be recommended to increase production and productivity of soybean in acidic soils of the study areas. However, the response of soybean having different maturity groups and use of different biological strains should further be tested in combination with liming and potassium fertilizer to come up with conclusive recommendations


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