ABSTRACT Arsenic (As) uptake by rice is mainly controlled by the redox potential, amount of iron- and aluminum-bearing minerals and silicon (Si) availability in paddy soil. These soil properties are altered upon long-term continuous rice cultivation, and differences in soil properties arising from different agricultural management practices can influence As behavior in soils. This study aimed to clarify how long-term soil management with and without liming and rice straw compost application influences As uptake by rice. Soil and rice samples were collected from plots with continuous application of NPK mineral fertilizer with and without lime and from plots applied with NPK mineral fertilizer and lime with 750 and 2250 g m−2 straw compost in a long-term experimental paddy field established in 1926. Concentrations of As in rice shoots and panicles from the 92nd to 97th cropping seasons were determined. Hydrochloric acid (1 mol L−1 HCl)-extractable As and pseudototal As concentrations were also determined in select archived soil samples collected from the 52nd to 97th cropping seasons and for the 97th cropping season, respectively. Arsenic uptake by rice was lowest in the plots with lime and 2250 g m−2 rice straw compost application because application of excess organic amendments induced strong reducing conditions, which resulted in a loss of As and Fe minerals from the soil. In this plot, As uptake was lower in the year when no precipitation occurred over a longer period of days during the mid-summer drainage. Despite the increase in the uptake of Si with the application of rice straw compost, the ability of Si to mitigate As uptake was not apparent. The uptake of As by rice in the plot without liming was lower although this plot had a higher concentration of HCl-extractable As in the soil, possibly because As dissolution under flooded conditions was suppressed by the presence of low-crystalline Al minerals. In conclusion, As uptake in rice decreased with the long-term application of excess rice straw compost and in the absence of liming.
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