ABSTRACT
Wetting and Drying (AWD) of the paddy soils during rice cultivation, i.e., in non-flooded conditions with supplemental irrigation promoting oxidation of arsenite in rice rhizosphere.
2 MATERIALS AND METHODS
A macrocosm study in pot experiment was performed using the rice variety BRRI dhan-11 on a silty clay loam soil (background As level was 1.6 mg/kg). The treatments used were three water regimes viz., at 100%, 75% and 50% of Field Capacity (FC) and three organic matter treatments, viz., cow dung, poultry manure and a mixture of both, applied at a rate of 5 tons/ha. In addition, another set of experiments was prepared with AWD. Two sets of control experiments were also included where both As-laden and As-free water were used at the 3 levels of FCs with no added organic matter. All experiments were performed in triplicates. Seedlings of the rice variety were transplanted into the pots and all the pots were arranged in a completely randomized way. Fertilizers were added as per direction of the Fertilizer Recommendation Guide 2005 (BARC 2005). 1 mg/L arsenic solution, in a combination of 80% arsenite (source: sodium meta-arsenite, NaAsO2) and 20% arsenate (sodium arsenate, Na2HAsO4.7H2O), was used as the As treatment. As accumulation in rice was analyzed using Atomic
1 INTRODUCTION
Arsenic (As) contamination of soil and groundwater has been termed the world’s biggest natural calamity in known human history (Imamul Huq 2008). The widespread use of As contaminated groundwater for irrigation has been reported to pose the risk of soil build up of As and its subsequent transfer to plants (Ali et al. 2003, Imamul Huq & Naidu 2005; Imamul Huq et al. 2006a; Williams et al. 2006; Meharg et al. 2001; Farid et al. 2003). In addition to this poisoning of the food chain due to increased As in soil-water-crop systems, its long-term impact on agricultural yield is also another major concern (Ali et al. 2003). Concerning this crucial issue, various mitigation strategies to reduce the As load in soil as well as its uptake by plants have been approached (Imamul Huq 2008). In the present study, a combination of some of these approaches were tried to assess the effectiveness of such mitigation measures to minimize arsenic toxicity in rice.
