The effect of sulphur in soil on the availability and uptake of metal nutrients

Abstract

Soils of Malta are classified as calcareous soils and slightly alkaline. They have poor soil horizon development with very shallow depths. They have a high pH and a CaCO₃ content, and these cause a negative impact on plants/crops by reducing the availability and solubility of certain elements which will eventually lead to element deficiencies. Soil treatment with S is common practice in alkaline soils in order to acidify them, thus reducing the pH and solubilizing CaCO₃, making plant nutrients more available to be absorbed by plant roots. The application of S for pH reduction in calcareous soils is not often very effective due to the buffering capacity of these soils. The scope of this work was to investigate the effect of S amendments in local calcareous soils. Different S doses were applied to calcareous Calcisol and Luvisol to determine the mobility, availability and uptake of nutrients by lettuce plants and also to record lettuce performance in terms of growth and yield, and the effect on soil pH and salinity. The study concluded that the NO₃⁻ content in lettuce sap increased in both soils. Regarding the PO₄³⁻ content in lettuce, S did not have a significant effect in the plants grown in the Luvisol whereas in the Calcisol the difference was significant. With regards to metal nutrients, the addition of S to the soil the plant uptake of Zn increased, whereas Ba and Mn decrease in both soils. As for Cu the difference in uptake by plants was only significant in the Luvisol. Conversely, S treatment did not affect the availability and uptake of Fe, Ni, Sr, Cr, Pb in both soils. With regards to crop height S application had no effect in both soils, however, the width of the plants in the Calcisol was greater in the S treated soil. No difference was noted in the plants grown in the Luvisol. Root growth and development, fresh mass, dry mass and % dry matter content of lettuce plants were not affected by S amendments in both soils. S treatment increased the soil EC and slightly lowered soil pH in both soils. It had significant effect on the NO₃⁻ where S made NO₃⁻ more mobile and available. S application also increased the EC of drain water, and it lowered the pH.