Arsenic mitigation strategy for rice, using water regime management

Abstract

The response of two varieties of rice plant (BR-28 and BR-29) to arsenic accumulation added from two sources (As III and As V ) under two different water regimes (100 and 75% of field capacity) were examined. Treatments added to soil were 0, 10, 20 and 40 mg As/kg soil. Plant samples were collected after 120 and 140 days from seed sowing, for BR-28 and BR-29 respectively. Delayed seedling emergence; reduced plant growth; yellowing and wilting of leaves; brown necrotic spots on old leaves; and, finally, reduced grain yield of the two varieties, confirmed the symptoms of As toxicity. Arsenic accumulation by plants growing with either As III or As V increased with increasing As treatment, irrespective of water regimes. However, the accumulation was greater in the arsenite-treated soil than that in the arsenate-treated one, indicating the higher phytoavailability of As III . Most of the As taken up by plants was sequestered in the root, followed by straw and grain. In roots of BR-28, the maximum As accumulation from arsenite-treated soil was 17.6 mg/kg dry weight (d.w.) at 100% field capacity (f.c.), whereas at 75% f.c. it was 15.4 mg/kg d.w. and for the roots of BR-29 the values were 31.04 mg/kg d.w and 22.65 mg/kg d.w. at 100 and 75% of f.c. respectively. Arsenic in straw and grain was lower for plants of both varieties at 75% of f.c. However, there have been some varietal differences in the response to As III or As V . The paper discusses the possible management of moisture regimes to reduce the phytoavailability of arsenic, thereby mitigating its toxicity in the rice crop.