Forms and fluxes of potential plant-available silicon in irrigated lowland rice production (Laguna, the Philippines)

Abstract

Silicon (Si) is beneficial for rice plants. It increases their resistance against pests and diseases. Although Si uptake of rice crops is often higher than nitrogen uptake, studies on forms and fluxes of plant-available Si in paddy systems are scarce. In 2011/12 we assessed acetate-, oxalate-, and carbonate-extractable Si in topsoil (i.e., Si forms that contribute to the pool of ‘readily soluble Si’) and related them to plant-Si-uptake (n = 10 paddies; Laguna region; Philippines). In the wet season 2013, we determined changes in (i) plant-Si-uptake, (ii) dissolved Si (dSi) and (iii) acetate-extractable Si in topsoils in a high temporal resolution (n = 5 paddies, every ~10 days), and assessed dSi fluxes via irrigation, rain, drainage and percolation (n = 3 paddies). Si storage in plants at harvest was 0.73 ± 0.12 Mg ha−1 (>78 % in straw), and not related to different Si forms in topsoils. Large stocks of carbonate-extractable Si (2–29 Mg ha−1) suggest an accumulation of ‘phytoliths’ (amorphous Si oxides in straw) in topsoil due to irrigation. Acetate-extractable Si in topsoils hardly changed during plant growth, suggesting dSi and absorded Si was continuously contributed by irrigation and phytolith dissolution. Geo-/pedologic conditions, irrigation, and straw management are major determinants on Si storage and fluxes in irrigated rice paddies.