Evaluation of Absorption and Uptake of Soil- and Foliar-Applied Silicon Fertilizer in Rice.

Silicon (Si) fertilization via soil amendments is an established agronomic practice in rice production systems. While active Si uptake by roots has been long-established, Si absorption through leaves remains contentious. Two greenhouse experiments were conducted to evaluate Si absorption and uptake by rice via soil- and foliar-application of Si fertilizer. First, three application rates of Si solution  (12, 24, and 36 g Si ha^-1) were sprayed to either whole rice plants or leaves of the primary third tiller of each plant at early tillering, booting, and early flowering rice stages. For the second experiment, Si solution (36 g Si ha^-1) was strictly applied to adaxial side of rice leaves at early tillering stage and after one week of standing, leaves were harvested and washed with 2% nitric acid (HNO₃) and deionized water. All treatments were replicated at least four times and arranged in a randomized complete block design. Both washed and unwashed leaf samples were examined using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDAX) and analyzed for Si content. Plant tissue samples’ elemental composition, soil Si and nutrient content, biomass, and yield were also determined. Washing had no effect on leaf Si content across rice growth stage. While foliar application of Si solution increased Si content in rice biomass at harvest by 4% (P<0.10), there was no significant effect observed on number of tiller and panicle, and straw and panicle yield. Based on SEM/EDAX analysis, upper leaf surface had higher Si concentration (7.75%) than the lower surface (P<0.01). Compared with the foliar treatment, wollastonite-treated rice still attained the higher leaf Si content (P<0.01). The outcomes of this series of greenhouse studies suggest that Si solution was not absorbed through rice leaves and that soil-applied Si thus far is the effective method of enhancing plant Si uptake.