Status of Mn and Fe in Agricultural Soils of Western Ethiopia: Laboratory Assessment

Abstract

One hundred and sixty soil samples at depth of 0-15 cm were collected from Nitisols of Western Ethiopia following three elevational positions (low, mid and high altitudes) at 1300, 1800 and 2300 masl, respectively, and two farming practices (traditional and intensive). The objectives of the study were to assess the status of manganese and iron in Nitisols and examine effects of altitude and farming practices on the status. The status was determined using diethylene triamine pentaacetic acid-triethanolamine (DTPA-TEA), ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA) and Mehlich III methods using atomic absorption spectrophotometer. There were no textural variation among all samples and all the samples were classified in the clay textural class. The pH measured in water varied between 4.24-6.21. Sixty four percent and fourteen percent of the samples were low in available phosphorus and organic carbon, respectively. Comparing the results of extractable manganese and iron in Nitisols of Western Ethiopia with critical levels of manganese and iron from literature, the amounts of extractable manganese and iron were in the sufficient range. The manganese status was higher in traditional farms than in intensive farms in low and high altitudes. In mid altitude, on the other hands, the status of manganese in intensive farms was higher than that in traditional ones. The iron status was mostly higher in traditional farms than in intensive farms in all altitudes. Irrespective of farming practices the status of manganese and iron increased with the increase in altitude. The amounts of manganese were higher than those of iron in all the three altitudes using the three methods. Comparing the extracting power of the methods used for determining manganese and iron, the result of soil analysis showed that DTPA-TEA was superior to the others followed by AB-DTPA and Mehlich III.