Field studies were established on the alluvial floodplain soils in Louisiana, from 2013 to 2015, to evaluate the effect of silicate slag applications on productivity of wheat (Triticum aestivum), under sufficient and high nitrogen (N) application rates. Treatments were arranged in a randomized complete block design, with four replications consisting of twelve treatments: a factorial combination of two N (101 and 145 kg N ha-1) and five silicate slag rates (0, 1, 2, 4.5, and 9 Mg ha-1), and two control plots (with and without lime). Nitrogen had a greater impact on wheat productivity than silicate slag application. Wheat grain yield reached over 7000 kg ha-1 with applications of 145 kg N, and 9 Mg silicate slag per ha for soil having Si level <20 mg kg-1. Yield increases due to N or Si were attributed to the increase in number of spike m-2 and grain number spike-1. Silicate slag application effectively raised soil pH, and availability of several plant-essential nutrients, including plant-available N (nitrate, NO₃-), demonstrating the benefits of slag application are beyond increasing plant-available Si. The benefits of silicate slag application were clearly observed in wheat supplied with high N, and on soil with low plant-available Si.
Keywords: grain yield; nitrogen; plant-essential nutrients; silicate slag; silicon; soil pH; wheat.