Reaction Classes and Phosphorus and Potassium Contents of Soils in Major Potato Growing Areas of West Shoa Zone as Determined through Different Methods

Poor soil fertility management has been one of the major factors constraining potato productivity on farmers’ field in Ethiopia, creating a wide gap between the actual yield and potential yield. A study was conducted in West Shoa Zone, Ethiopia to investigate the reaction classes as well as phosphorus and potassium contents of soils of farmers managed potato farms. Soil samples, from a depth of 0-30 cm, were collected from six districts during the Belg (March-June) cropping season to determine pH, phosphorus and potassium contents. Soil pH was determined using both water and 0.01 M calcium chloride solutions. Available phosphorus content in the soil was determined using both CAL and Olsen methods. Potassium content of the soil was determined both by extracting the potassium with Calcium Acetate Lactate (CAL) solution as well as by 1 M ammonium acetate solution. Results showed that the soil pH in all the districts was generally low, the average soil pH determined in CaCl2 suspension ranged between 4.9-5.5. Most of the fields sampled in Chelia, Welmera, Ejere, Tikur-Inchini and Jibat districts had low and very low CAL-P value while all the fields sampled in Jeldu district had CAL-P only in the target, high and very high classes. 58.5% of the sampled fields had a CAL-K value in the very high class and above. 56% of the sampled fields had an ammonium acetate extractable K content in a class ranging from moderately high to very high. Nearly 70% of the fields had low, very low and extremely low according to Olsen P test. Only 9.5% of the surveyed field soil was rated as having low or very low Olsen P while 80.5% had K content of target value and above.