Effect of Granular Size of Silicate Slag on Silicon Availability in Soils and Uptake By Wheat (Triticum aestivum).

Silicate slag application is a recognized agronomic practice for rice and sugarcane cultivation but limited research has been done on the effect of granular size on the silicon (Si) supplying capacity of silicate slag to wheat. The purpose of this study is to document the effect of different granular size of silicate slag on the availability of monosilicic acid (H₄SiO₄) to wheat. Four granular size fractions (fine - 100% < 0.1 mm, coarse - 100% > 0.1 and < 0.15 mm, pellet - 100% > 1 mm < 3.4 mm, and whole - a mixture of fine, coarse and pellet) of silicate slag from two sources (Slag-1 and Slag-2) and wollastonite were incorporated to soil at the rates of 0, 125, 250, 500 and 1000 kg Si ha^-1 in a pot trial before sowing wheat. Treatments were arranged in a randomized complete block design with four replications. For both slag sources, the concentration of H₄SiO₄ increased with decreasing granular size with fine material releasing H₄SiO₄ at an average rate of 0.40 µg for each g of Si applied (r²=0.94), followed by wollastonite, coarse, whole and pellet. The H₄SiO₄ level was maintained above 250, 150, and 100 mg Si kg^-1 from 30 to 120 days after the application of fine, whole, and course/pellet granular sized slag, respectively. Source has no evident effect on the amount of H₄SiO₄ released. The highest grain yield was 4.4 Mg ha^-1 from wollastonite- and whole-slag -treated soil. It is likely that granular size of slag influences its Si supplying power; however, increasing soil Si is not a guarantee for increase yield in wheat. The use of smaller granular size would be an effective way of lowering application rate of slag in Si depleted soils.