Abstract

Post-fertilization changes in soil micronutrients were explored in three locations on lands cultivated for wheat in Ethiopia. For this purpose, 15 and 30 soil samples were collected, respectively, before planting and after harvest from 120 cm deep nine pedons. The samples were collected from middle-blocks at five-depth intervals. After harvest, samples were collected only from the check/control and full-dose Nitrogen-Phosphorus-Sulfur-Calcium (69:20:18:23 kg/ha, respectively) applied units, excluding the intermediates. The results revealed that the lands had been under intensive cultivation for several decades without external additions of micronutrients-containing inorganic fertilizers. However, the analyzed soils always contained some small/suboptimal amounts of micronutrients at all depths, with a very narrow scale of variability. The micronutrients Fe, Zn, B, and Mo were severely low in the initial topsoil, with a 10–40% decline soon after wheat harvest. Depth-wise, Mn, B, Mo, and other properties like pH, clay content, and bulk density increased with depth, whereas OC, Cu, Fe, and Zn followed reverse trends. Such spatial variations in soil properties were conceived to be largely affected by pH, particle size, clay mineralogy, and the amounts/rates of biomass recycling. A high degree of correlation was found among the variables. In this regard, Mo showed a strong inverse relation with the rest of the micronutrients, which may indicate its antagonistic effect with them. Organic carbon showed a strong positive relation with all the micronutrients, except Cu and Mo, which may affirm the critical role played by organic matter mineralization in micronutrients speciation and/or organic resource's role for the immediate best soil conditions. Other potential sources of soil micronutrients can be the subject of further investigations. 

Key words: Post-fertilization-changes, soil-micronutrients, soil-profile, leaching-loss, biomass-recycling, organic matter mineralization, several-decades