Micro nutrient status and their distribution in aggregate-size fractions of tropical coastal plain sands under different land use

Micro nutrients are particularly sensitive to changes in land use and their availability in soil is influenced by their distribution and storage in stable aggregate fractions. Micro nutrient, (Fe, Mn and Zn) status and their storage in stable aggregate-size fractions in forested, rubber plantation, oil palm plantation, plantain plantation, and cassava soils were investigated. The result indicated that there were significant variations in Fe, Mn and Zn storage in whole soil and stable aggregates of the different land use types. Land use also led to changes in soil organic matter (SOM), pH and total N. The highest total N (4.7 mg kg-1) was found in the 0-15 cm depth in forested soil, whereas, the lowest (2.3 mg kg-1) was found in the rubber plantation soil. The highest Fe was found in oil palm and plantain plantation soils (103.7 and 89.6 mg kg-1) respectively, in the topsoil, and 132.7 mg kg-1 and 91.4 mg kg-1 in the subsoil. Plantain plantation had the highest Zn and Mn storage in micro aggregates in the top and subsoil. Cassava plots had greater Fe and Zn storage in macro aggregates. This indicates that breakdown of macro aggregates to smaller fractions during cultivation in may lead to significant loss of Fe and Zn in cassava plots. Manganese (Mn) deficiency may likely occur in plantain plantation if the soil is converted to arable cropping. Iron (Fe) and Zn showed significantly negative relationship with pH (r = -0.461 and r = -0.645) respectively, indicating the significant role of soil pH in Fe and Zn availability in soils. Relationship between soil mineral particles showed that Mn increased as sand content increases, but showed inverse relationship with silt. Oil palm and plantain soils are good sources of Fe and Zn, and can be utilized in areas where these micro nutrients are limiting arable crop production.Keywords: Stable aggregates, soil fertility, micro nutrient deficiency, organic matter, and nutrient storage.