MICRONUTRIENT STATUS OF SELECTED CACAO-GROWING SOILS IN SOUTHWESTERN NIGERIA: PROFILE DISTRIBUTION OF TOTAL AND AVAILABLE ZINC

Abstract

A study was conducted to determine the content and distribution of total 1.0 M NH4OAc-, 0.1 M HCl-, 1 M MgCl2-, and 0.005 M DTPA-extractable Zn in the genetic horizons of 16 soil profiles from major cacao-growing areas in Southwestern Nigeria. The content of total Zn for all the soils varied from 12 to 92 μg/g with soils derived from igneous and metamorphic rocks containing more than those of sedimentary origin. Most of the soils had the highest concentration of total Zn in the surface horizons. There was a strong association between total Zn and organic matter, total Zn and silt/clay content. The 1 M NH4OAc-, 0.1 M NCl-, 1 M MgCl2- and 0.005 M DTPA-extractable Zn in all the soils and horizons varied from 0.17 to 5.6, from 0.06 to 2.37, from 0.20 to 1.20 and from 0.022 to 1.14 μg Zn/g, respectively. The NH4OAc generally removed more Zn than the other three extractants. The amount of Zn extracted showed a general decrease with depth. A significant amount of MgCl2-extractable Zn appeared to be associated with silt content while soil pH influenced the quantity of Zn extracted by the NH4OAc method. Key words: Total Zn, NH4OAc-extractable N, HCl-extractable N, MgCl2-extractable N, DTPA-extractable Zn, soil profile