Silicon transfers in a rice field in Camargue (France)

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. (c) 2005 Elsevier B.V All rights reserved.