Redox-Related Behavior of Zinc in Noncalcareous Paddy Soils.

Zinc plays a key role in the normal growth and production of rice plants. An inadequate amount of available zinc in the soil can reduce the yield and nutritional quality of the plant, causing zinc deficiency among rice consumers. A microcosm experiment of stirred soil slurry was conducted to explain how sulfide formation and reductive dissolution of iron and manganese affect zinc solubility. The slurry was made anaerobic by continuous addition of nitrogen, which resulted in a change in redox potential from +200 mV to -300 mV. During the 4-week reaction time, soil solution samples were collected repeatedly through microporous tube samplers for analysis of sulfate, sulfide, and water-soluble zinc, iron, and manganese. Geochemical modeling (Visual Minteq) of the measured data from four contrasting soils suggested that sorption of metals onto iron and manganese oxides, in addition to sulfide precipitation, were the main factors that decreased Zn solubility at low redox potential in the soils. This study provides an understanding of which soil properties are important in predicting the likelihood of a decrease in zinc availability after flooding and how redox-driven reactions such as sorption and precipitation could release the zinc in the soil.