Reduction of the risk of arsenic accumulation in rice by the water management and material application in relation to phosphate status

To reduce the risk of excessive arsenic (As) in rice by using agronomic methods applicable to common farming in uncontaminated soil with As, we examined the effect of different start periods of drainage after heading and the application of iron (Fe) or silicate (Si) materials in concrete frames filled with soil collected from an area surrounding a former As-polluted region. The concentration of As in the grain decreased with the early start of drainage, whereas the cadmium (Cd) concentration increased. Thus, maintaining the oxidative condition after heading significantly decreases the concentration of As in the grain. Fe material application significantly decreased the concentration of As in the grain compared to the control. The phosphorus (P) concentration ratio of grain to straw (which we regarded as the P distribution rate of grain and straw) was significantly lower with the delay of the start of drainage. Similar results were obtained in the solution culture experiment in which the P level was decreased by half in the culture solution. A negative correlation between the P concentration ratio of grain to straw and the concentration of As in the grain was observed, indicating that an increase in the P translocation rate from straw to grain would inhibit the accumulation of As in the grain due to the competition of P and As. Further evaluations of the effects of Fe, Si, and P on water management and fertilization are needed to reduce the risk of As accumulation in rice grain.