Potassium forms of soils under enset farming systems and their relationships with some soil selected physico-chemical properties in Sidama zone, Southern Ethiopia

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Soil potassium is classified as unavailable, readily available and slowly available (fixed) K forms. A research was conducted to determine the distribution of forms of K (water soluble K, exchangeable K, non-exchangeable K and total K) and their relation with some soil properties under enset farming systems of Sidama zone in South Ethiopia. The soils were collected from ‘Qola’ (dry, hot tropical climate and moist to humid), ’Woinadega’ (warm subtropical climate) and ‘Dega’ (wet and cool temperate climate). In the study, coefficient of variance (CV%) for sand, soil organic matter (SOM), total nitrogen (TN), available phosphorus, water soluble K, exchangeable K, non-exchangeable K and percent potassium saturation were high (>30%). The high, medium and low proportions of acidic reaction were determined in Hula, Dale and Hawassa-Zuriya districts, respectively. The concentrations of total K in the soils ranged from 1358.9 to 3181.5 (mg/kg) where the Hula district soil show the lowest value. Water soluble K and exchangeable K concentrations in the soils ranged from 14.7 to 110.5 mg/kg and 130.9 to 1134.9 mg/kg, respectively, where the lowest values were indicated by Hula district. The Hawassa-Zuriya district soils had the highest concentrations in both exchangeable and water soluble K. The non-exchangeable K concentrations varied from 241.5 to 1714.9 mg/kg. It constituted the highest proportion of the total K measured in the soils, while the proportion of water soluble K in the total K measured was the lowest. Nearly all soils of Hula and Dale districts indicated low ratio of K:Mg. Almost all of the Hula district soils and about 50% of the Dale district soils had potassium saturation percent (KSP) values below critical level. Significant indirect and direct associations existed among soil physico-chemical properties. All forms of soil K correlated significantly and positively with pH, PBS and silt, and negatively correlated with SOM and Al+3. Key words: Water soluble K, exchangeable K, non-exchangeable K, total K, organic matter, cation exchange capacity.