Mobilisation of arsenic in soils and in rice (Oryza sativa L.) plants affected by organic matter and zinc application in irrigation water contaminated with arsenic

Experiments were conducted to study the effects of arsenic-contaminated irrigation water, zinc and organic matter on the mobilization of As in an Aeric Endoaquept in relation to rice (cv. IET 4786). Our results show that the amount of extractable As increased with the progress of submergence and decreased with Zn application. The magnitude of such decrease varied with the amount of Zn. The As content in soil markedly decreased with organic matter application, especially with farmyard manure. The results of the greenhouse experiment with exposure of graded doses of As to rice suggest that the upper toxic limit of As in soil was 10 mg/kg for rice. The results of the field experiment show that the grain yield of continuous flooding (4.84 t/ha) and intermittent flooding up to 40 days after transplanting followed by continuous flooding (4.83 t/ha) with the application of ZnSO4 at the rate of 25 kg/ha did not vary significantly. The lowest grain yield (3.65 t/ha) was recorded in the treatment where the intermittent flooding was maintained throughout the growth period without the application of Zn. The amount of As was, however, much lower in the treatment where intermittent flooding was maintained throughout the growing period combined with zinc sulphate application.