Evaluating Calcium Silicate Slag in Rice Production:Trace Contaminants and Drought Stress Alleviation.

Calcium silicate slag from phosphorus fertilizer industry is potentially a good source of Si for rice production. However, this type of slag contains trace elements that have the potential to contaminate rice grain and straw. Before land application, it is necessary to evaluate the slag’s effect on solubility and bioavailability of trace contaminants. Silicon has been reported to reduce drought stress on many crops, but limited studies have evaluated this effect with rice using calcium silicate slag as a source of Si. Two greenhouse studies were performed to address these issues. Four slag rates (0, 1000, 2000, 4000 mg kg^-1) were surface applied or incorporated into an organic soil and a mineral soil for trace contaminants determination. The same rates and application methods were evaluated under flooded and drought-stressed conditions on a mineral soil for drought stress mitigation. Results showed that applied slag increased soil pH, Si availability, and rice biomass. Total concentration of evaluated trace contaminants and total radioactivity in soils and rice grain was not affected by slag application. Plant available Cu and Zn in the organic soil increased, whereas Ni in the mineral soil decreased following slag application. Under drought stress, added slag increased foliage density, photosynthesis, transpiration, carbon isotope discrimination, and sugar accumulation in rice leaf, but decreased proline accumulation in leaf. This research indicates that the environmental risks of using calcium silicate slag is minimal and that it may benefit rice production by improving Si availability and reducing drought stress.