Variability of soil micro-nutrients under continuous cultivation in Nigerian Savanna.

Abstract

This study examined variability of soil micro-nutrients under continuous cultivation in Nigerian Savanna. Soil samples were collected from eight irrigated farm plots in Zaria while uncultivated nearby land was used as the control. Soil samples were taken from two depths: 0-15cm (top soil) and 15-30cm (sub soil) in two seasons: Wet Season (WS) and Dry Season (DS) respectively. In all, 9 composite soil samples from 216 sampling points were analyzed using standard laboratory methods. Soil samples were subjected to wet ashing using sulphuric and hydrofluoric acids. The solutions thus obtained were used for the determination of the following metals: Iron (Fe), Cupper (Cu), Manganese (Mn), Zinc (Zn), Lead (Pb), Nickel (Ni) and Chromium (Cr) using Atomic Absorption Spectrophotometer (AAS). Descriptive statistic was used to describe and compare the results while Pearson Correlation Coefficient was used to test the levels of significant of the elements at 0.01 and 0.05 with the use of SPSS. The results obtained varied considerably between the top and sub soils and between the dry and the wet seasons. With the exception of Mn which reduced by 9% at both layers and Co which reduced by 7% (sub soil), all other elements showed an increase of between 11 and 54% in WS over the DS. It is recommended that soil and in addition crop testing should be carried out from time to time in order to know the levels of concentration of these metals.