Silicon Fertilization in Rice: Establishment of Critical Silicon Level and Its Impact on Availability of Nutrients in Soils of Louisiana.

While silicon (Si) fertilization is widely practiced in paddy rice production, the establishment of critical soil Si levels has remained understudied.  This study was undertaken to: 1) determine the critical soil Si level for rice production in Louisiana using different extraction procedures, and 2) document the effect of enhanced Si content in rice panicle on the uptake and content of select plant essential nutrients. Field trials were established in 12 sites across Louisiana from 2013 to 2015. Before planting, Si was applied as calcium silicate slag (CaSiO₃, 12% Si) at the rates of 0, 1, 2, 3, 4, 6, and 8 MT ha^-1.  Agricultural lime was also applied (2 and 4 MT ha^-1) to control plots to evaluate the liming effect of CaSiO₃ slag in the main treatments.  Treatments were arranged in a randomized complete block design with four replications. Straw and panicle samples were analyzed for Si and nutrient content while Si content of collected soil samples was determined based on different extraction procedures. There were weak positive correlations between panicle Si uptake and soil Si content extracted by acetic acid (r² =0.21) and citric acid (r² =0.23) solutions. Straw Si uptake and soil Si content  based on 0.5 M ammonium acetate procedure obtained a stronger relationship with an r² value of 0.35 and with an estimated critical Si level of 52 ug g^-1 based on Cate-Nelson analysis. Positive correlations (r²>0.2) were also observed between total Si uptake and soil Si concentration using all extractants. In selected sites, panicle Si content had a strong negative relationship (r²= 0.75) with sulfur content whereas two sites showed an increased in iron content (r²=0.48). When pooled across sites and years, only sulfur content maintained a clear but weak relationship with Si (r²=0.11).  Estimated critical soil Si levels varied with different soil type and extractant.