Micronutrient Status of Grain Size Fractions in Soils of Land Uses in Mbano, Southeastern, Nigeria

Micronutrient status in grain size fractions provides information on the active soil fraction and the ability for stabilization against microbial decomposition. Total, available, exchangeable and water-soluble Fe, Zn,Cu and Mn in bulk and grain size soil fractions were evaluated in three landuse types (Cassava, Cashew and Oil palm) in Ehime Mbano, Southeastern, Nigeria. Also, selected soil properties (pH, O.M, ECEC, clay, silt, Ca and P) were correlated with bulk soil micronutri- ents using correlation analysis. Equally, micronutrient in grain size soil fractions was regressed with bulk soil contents using regression analysis. Total, available, exchangeable and water-soluble micronutrients ranged from 1389.08-2350.06, 75.07-166.61, 73.43-163.45 and 1.64-8.04 (Fe), 12.93-21.88, 3.08-3.22, 2.31- 2.56 and 0.62-0.77 (Zn), 0.39-4.11, 0.21-0.64, 0.12-0.37 and 0.09-0.27 (Cu) and 127.62-215.96, 27.06-28.25, 19.80-21.94 and 5.85-7.26 mg kg-1 (Mn) respective- ly. Whereas, total and available Fe, Mn and Zn, exchangeable Fe and all Cu were significantly (LSD 0.05) higher in Oil palm, exchangeable Mn and Zn and water- soluble Mn and Zn were higher in cashew and cassava landuse types respective- ly. Also most bulk soil micronutrients were significantly (P < 0.05) correlated with soil pH, O.M, sand, silt and clay but not with C.E.C and exchangeable Ca. Equally, micronutrient distribution varied amongst grain size soil fractions with most distinctly higher in Oil palm land use. Furthermore, averaged over land use types, clay size fraction was more enriched with most micronutrients. Finally, more than 95% of bulk soil micronutrients could be accounted for by the grain size soils fractions and with the contribution of each grain fraction being equal.