Silicon transfers in a rice field in Camargue (France)

Abstract

We conducted a study of the biogeochemical cycle of silicon in a rice field in Camargue (France) in order to evaluate the role of biogenic silicon particles (BSi) in the cycle. Opal-A biogenic particles (phytoliths, diatoms…), which dissolve more rapidly than other forms of silicate usually present in soils, are postulated to represent the easiest bioavailable Si for rice. We found 0.03–0.06 wt.% of BSi in soils (mainly phytoliths). This value is lower than other values from the literature. Each year, the exportation of BSi from rice cultivation is 270 ± 80 kg Si ha − 1 . We show that BSi input by irrigation is mostly composed of diatoms and we estimate it at 100 kg Si ha − 1 year − 1 . This value is more than a third of the annual Si need for rice. The budget of the dissolved silicon (DSi) fluxes gives the following results: the atmospheric and irrigation inputs represents 1% and roughly 10%, respectively, of the annual need for rice; the drainage and infiltration outputs represent 17 ± 14 and 12 ± 9 kg Si ha − 1 year − 1 , respectively; the balance of our budget shows that at least 170 kg Si ha − 1 year − 1 are exported from the soil. If we consider the soil BSi as the only source of dissolved silicon, this stock could be exhausted in 5 years.