Silicon fertilizers mitigate rice cadmium and arsenic uptake in a 4-year field trial

Abstract

Comparatively few field experiments have been conducted to monitor the long-term effects of Si fertilizer amendments on the mitigation of Cd and As accumulation in rice grains. A 4-year field trial (eight growing seasons) was established in paddy fields to investigate the effects of different Si fertilizers on the mitigation of Cd and As uptake in rice cultivars. Cultivars for the spring and summer growing seasons were chosen based on their local popularity to investigate the effect of Si fertilizers on different cultivars. Average Cd concentrations in spring rice grains (0.020 ± 0.006 mg/kg) were much lower than those in summer rice grains (0.416 ± 0.370 mg/kg) regardless of rice cultivar. Spring rice grains contained slightly higher average As concentrations (0.43 ± 0.07 mg/kg) than summer rice grains (0.30 ± 0.09 mg/kg). Silicon fertilizers, except sodium silicate, significantly decreased grain Cd concentrations. Calcium silicate fertilizer substantially decreased grain Cd, by up to 55.1 ± 17.6%, and to a greater extent than that in response to Si-potash fertilizer, by up to 26.4 ± 7.9%, probably because of competition between Cd and Ca for Ca transport channels. Slow-release Si fertilizer resulted in the greatest decrease in grain Cd concentration (69.0% ± 8.6%). Slow-release fertilizer may provide a longer-term Si source and higher efficiency of use for rice than readily soluble Si. Silicon fertilizers substantially reduced Cd, but not As, concentrations in summer rice grains for a long term (eight growing seasons). Calcium silicate fertilizer reduced grain Cd concentrations more significantly than potassium silicate fertilizer. Calcium silicate fertilizer exhibited higher efficacy of Cd reduction in grains regardless of rice cultivar or growing season. Slow-release Si fertilizer showed superior ability for Cd mitigation than that of soluble Si fertilizers.