Status of Cu, Zn, B and Mo in Agricultural Soils of Western Ethiopia: Laboratory Assessment

Abstract

               One hundred and sixty soil samples of Nitisols of Western Ethiopia were collected following three elevational positions and two farming practices. The objectives of the study were to assess the status of copper, zinc, boron and molybdenum in the soils and to examine effects of altitude and farming practices on status of the nutrients. The status of copper and zinc were determined by diethylene triamine pentaacetic acid-triethanolamine (DTPA-TEA), ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA) and Mehlich-III methods using atomic absorption spectrophotometer. Boron was analyzed by hot water extraction method and molybdenum by ammonium acetate EDTA extraction method using spectrophotometer. The contents of extractable copper were in the sufficient ranges by DTPA-TEA and AB-DTPA methods. However, by Mehlich-III method the amounts of extractable copper of 18, 3.6 and 1.8% of the samples were below the critical level in low, mid and high altitudes, respectively. The contents of extractable Zn were all in the deficient ranges in low and mid altitudes by DTPA-TEA and Mehlich-III methods. However, by AB-DTPA method, the contents of 72 and 51% of the samples were below critical level in low and mid altitudes, respectively. The contents of extractable Zn were in the deficient range in high altitude by 73, 9 and 71% of the samples using DTPA-TEA, ABDTPA and Mehlich-III, respectively. The contents of extractable boron in 30, 38 and 27% of the samples and the contents of molybdenum in 6, 2 and 6% of the samples were in the deficient range in low, mid and high altitudes, respectively. The contents of copper were higher in traditional farms than in intensive farms in low altitude, while the contents were mostly higher in intensive farms than in traditional farms in mid and high altitudes. 

                 The amounts of extractable zinc were higher in intensive farms than traditional farms. The values of extractable boron and extractable molybdenum mostly were higher in traditional farms than in intensive farms in all altitudes. The amounts of copper and zinc by Mehlich-III and AB-DTPA methods increased with increase in altitudes. Boron and molybdenum did not show consistency in the effects of altitudes.