Total and double-acid extractable copper and its adsorption characteristics in selected soils in Kenya

Abstract

An investigation was conducted to determine the content and profile distribution of total copper (perchloric acid extractable) and double-acid (0.05N HCl + 0.025N H2SO4) extractable copper and its adsorption characteristics in surface lli1d subsurface soils representing Andisols, Nitisols and Cambisols. The means of total copper in the A horizons of Kabete, Gituamba, Njoro lli1dNaivasha soils were 26.6, 29.3, 3.3 and 8.9 ppm respectively and the means for the B horizons were 24.6, 31.3, 3.1 and 9.7 ppm respectively. Total copper was found to be generally uniformly distributed with depth. This uniformity was attributed to the low mobility of coper in soil. The means of the double-acid (DA) extractable copper in the A horizons of the same soils (i.e. Kabete, Gituamba, Njoro and Naivasha) were 0.08, 0.36, 0.18 and 0.09 ppm respectively lli1dthe melli1Sfor the B horizons were 0.23, 0.39, 0.22 and 0.06 ppm respectively. Total and DA-extractable copper contents were correlated with soil pH, organic carbon and CEC. There was no si@1ificant correlation between total copper and CEC, organic carbon, pH or DA-extractable copper. A significant non-linear relationship was found between DA-e~tractable copper and CEC in Naivasha soil (r2=0.77). The copper adsorption maxima were 299 ~ Cu/g for Naivasha soil, 264 j..lCgu/g for Gituamba soil, 260 j..lCgu/g for Kabete soil and 164 ~ Cu/g for Njoro soil. The adsorption maximum was highly correlated to organic carbon and CEC except in Kabete soil.