Adsorption and desorption of copper and zinc in tropical peat soils of Sarawak, Malaysia

Abstract

Tropical peat soils are inherently deficient in micronutrients particularly copper (Cu) and zinc (Zn). In addition, limited information is available on the adsorption and desorption of these micronutrients in these soils, which are important factors governing nutrient concentration in the soil solution and nutrient availability to plants. A study was carried out to quantify adsorption and desorption of Cu and Zn in three untreated and limed tropical peat soils of Sarawak, Malaysia. Copper and Zn adsorption increased gradually with increasing levels of added Cu and Zn in both control and limed soils. The adsorption of Cu and Zn in limed soils increased by 50 and 67 fold, respectively, relative to control soils. The Freundlich constant (KF) values for Cu in both control and limed peat soils were higher than for Zn indicating that Cu is more strongly adsorbed to the soil solid phase than Zn. The KF values for Cu and Zn in this study were higher than those reported for other soil types. The percentage of adsorbed Cu and Zn susceptible to desorption into 5mM DTPA was higher than that desorbed by 10mM Ca(NO3)2 in all soils. A higher percentage of Cu than that of Zn was desorbed by DTPA because Cu has a higher critical stability constant with DTPA. Liming is necessary to increase the pH of peat soils but it also inevitably decreases the solubility and hence the bioavailability of Cu and Zn. This study provides evidence on the importance of adsorption and desorption data for estimating nutrient availability for plant uptake in tropical peat soils.