Soil and irigation management options to limit uptake of cadmium to rice plant grown in cadmium contaminated paddy soils

Abstract

From the researches conducted during 2003-2005 by the International Water Management Institute, the Land Development Department and Chulalongkorn University have unequivocally identified high levels of cadmium (Cd) in soils and rice grains in Phatat Pha Daeng sub-district, Mae Sot district, Tak Province, northern Thailand. This issue has raised the environmental and health concerns since then. Consequently, paddy fields in some areas have been prohibited for rice planting in order to avoid the problem of Cd uptake to plants and then transfer to the food chain. Therefore, this study aimed to investigate the farming practices that could reduce Cd uptake to rice plants. Four different treatments were set up for experimental pots containing contaminated soil from Mae Sot; namely, 1) normal practice by farmers, 2) rice straw adding to the studied soil, 3) liming agent (CaO) adding to the studied soil, and 4) rice straw and liming agent adding to the studied soil. Each of these four treatments were divided into two different procedures; drainage and flooding twice during the whole period of planting. So, there were 8 treatments all together and in each treatment, 3 replications were carried out. For drainage practice, two periods were designed to drain water from the experimental pots; 75 days after transplanting and before harvesting (125 days after transplanting). For these two periods, soil redox potential and pH in soil solution for all pots were measured. In addition, soil solution, soil sample, and rice plant were collected from both periods to determine Cd, Zn, Mn and Fe concentrations. The result shows that in most cases, Cd in soil solution directly related to Cd uptake to rice plants. The flooding practice in all cases reduced Cd uptake as compared to drainage practice because the reducing condition that occurred in the flooding practice minimized Cd transformation into is solution from. However, the treatments by adding rice straw and lime or both of them did not reduce Cd uptake as expected. It is believed that because of correlation among other metals and competition that may promote or inhibit Cd to be available form. So, from this study, it can be concluded only that flooding practice is better than drainage practice in term of reducing Cd uptake to rice plant.