How Rice (Oryza sativa L.) Responds to Elevated As under Different Si-Rich Soil Amendments

Several strategies exist to mitigate As impacts on rice and each has its set of trade-offs with respect to yield, inorganic As content in grain, and CH4 emissions. The addition of Si to paddy soil can decrease As uptake by rice but how rice will respond to elevated As when soil is amended with Si-rich materials is unresolved. Here, we evaluated yield impacts and grain As content and speciation in rice exposed to elevated As in response to different Si-rich soil amendments including rice husk, rice husk ash, and CaSiO3 in a pot study. We found that As-induced yield losses were alleviated by Husk amendment, partially alleviated by Ash amendment, and not affected by CaSiO3 amendment. Furthermore, Husk was the only tested Si-amendment to significantly decrease grain As concentrations. Husk amendment was likely effective at decreasing grain As and improving yield because it provided more plant-available Si, particularly during the reproductive and ripening phases. Both Husk and Ash provided K, which also played a role in yield improvement. This study demonstrates that while Si-rich amendments can affect rice uptake of As, the kinetics of Si dissolution and nutrient availability can also affect As uptake and toxicity in rice.