The beneficial effect of silicon to reduce the nitrate content of sorghum

Abstract

Purpose: Sorghum [Sorghum bicolor (L.) Moench] is one of the major fodder crops. Supplying sorghum with a sufficient amount of nitrogen (N) is essential to achieve a good yield and quality of forage. However, N excess may cause an accumulation of nitrate in the plant, which can be toxic to ruminant livestock animals. Silicon (Si) application reportedly enhances the utilization of N and reduces the nitrate content in several plant species. However, our knowledge is still limited regarding the interaction between Si and N in sorghum. Hence, this study investigated the possibility of nitrate content reduction by Si application in sorghum. Methods: We analyzed the nitrate content in the shoot of hydroponically grown seedlings, with or without Si application. It was then further evaluated in mature plants under high N supply with 0, 25, 50, 75, or 100 mg SiO2 L–1. We also considered possible mechanisms of the Si-N interaction. Results: The application of Si reduced nitrate content without significantly affecting the growth and dry matter production. The effect of Si application on the N metabolism of sorghum plants was confirmed by a modulated expression of the genes for N transport and assimilation, in which an upregulation of the cytokinin signal transduction pathway might be involved. In addition, the in vitro digestibility was not significantly affected by Si application. Conclusion: Silicon application has a beneficial effect on fodder sorghum production in reducing nitrate content without compromising the biomass yield and quality.