The response of the soluble- exchangeable form and bioavailability of heavy metals in saline-sodic and non-saline soils to two contrasting moisture treatments

Moisture and temperature have significant effects on soil characteristics [1]. Mobility and bioavailability of heavy metals are dependent on their chemical forms in soil [2]. The aim of this study was to evaluate and compare the effect of two moisture treatments (flooding and field capacity) by irrigation with potable water on transformation of heavy metals in saline and sodic and non-saline soils during one years with three sampling times (1, 150 and 365 days). Soil samples were taken from the surface layer of Kerahrood agricultural land (the non-saline soil) and Mighan playa (the saline soil). The Fe, Mn, Pb and Cd were extracted with KNO3 and distilled water (KNO3 extractable forms of metals) and DTPA (DTPA extractable form of metals) [3]. Analysis of variance and Duncan means test were done. Results showed that the redox potential (Eh) was decreased continuously in all treatments. The decrease of Eh in flooded non-saline soil compared to that in saline and sodic soil was more obvious. It was from 338 mv at the 1st day to -291 mv at the 365th day. Soil pH was decreased in 150th day in all treatments and then increased in 365th day of soil incubation. The changes of soil EC were similar to pH changes, but only in the saline-sodic soil these changes were significant. Total organic carbon (TOC) was increased in saline-sodic soil and decreased in non-saline soil continuously during incubation time. The soils incubated in flooding treatment had low levels of pH and Eh and high amounts of TOC that cause the metals would be more extracted by KNO3 and DTPA compared to their extractability in the field capacity treatment. The reduction of soil Eh in the flooded saline-soidic soil was significantly less than that in the flooded non-saline soil, therefore the KNO3 and DTPA extractable metals in saline-sodic soil were lesser may due to lower microbial activity. This finding may be related to lower microbial activity in the saline-sodic soil.