631 AJCS 12(04):631-638 (2018) ISSN:1835-2707 doi: 10.21475/ajcs.18.12.04.pne967 Physiological quality and dry mass production of Sorghum bicolor following silicon (Si) foliar application Rilner Alves Flores 1* , Everton Martins Arruda 2 , Virgínia Damin 1 , Jonas Pereira Souza Junior 3 , Deyvid Diego Carvalho Maranhão 4 , Marcus André Ribeiro Correia 5 , Renato de Mello Prado 3 1 Soil Sector, Agronomy School, Federal University of Goiás, Goiânia, Brazil 2 University of the State of Mato Grosso, Campus of Nova Mutum, Nova Mutum, Brazil 3 Department of Soil and Fertilizers, Paulista State University, Jaboticabal, Brazil 4 Department of Soil Science, Rural Federal University of Rio de Janeiro, Seropédica, Brazil 5 Federal Institute of Tocantins, Campus of Colinas do Tocantins, Colinas do Tocantins, Brazil * Corresponding author: rilner1@hotmail.com Abstract The forthcoming of silicon (Si) highly soluble sources provided a suitable alternative to Si use in agroecosystems. There are many benefits associated to Si application in crops, such as improvement in feed quality. In this sense, the aim of this work was to evaluate the effect of Si foliar application on physiological quality, biomass production, and silicon accumulation in Sorghum bicolor. The experiment was conducted under greenhouse condition using an entirely randomized design, with five Si rates (0 as control), 0.84, 1.68, 2.52, and 3.36g L -1 of Si) applied as potassium and sodium silicate, with four repetitions. In each treatment, applied solutions were balanced in potassium in order to isolate the Si effect. The following measurements were taken: growth, biomass production, Si accumulation, and physiological quality. Supplying Si via leaves did not affect the sorghum growth rate and the relative chlorophyll index; however, leaf area increased 23% with the use of 2.36 g L -1 of Si. Physiological variables are influenced by increasing Si rates, with rates close to 1.68 g L -1 of Si causing the best photosynthetic rates and stomatal conductance. The use of potassium silicate as a source of silicon is an alternative for productivity increases up to 30%, but an economic study on the viability of its commercial application in the production chain of Sorghum bicolor is necessary. Keywords: Silicon fertilization; beneficial element; mineral plant nutrition; photosynthesis; stomata conductance; relative chlorophyll index; transpiration. Abbreviations: Si_Silicon; pH_hydrogen potential; Al_aluminum; P_phosphorus; K_potassium; Mg_magnesium; SO 4 2- _sulfate; Zn_zinc; B_boron; H_hydrogen; CEC_cation exchange capacity; V%_base saturation; ERD_randomized experimental design; MAP_monoammonium phosphate; KCl_potassium chloride; PRNT_relative total neutralization power; DAE_days after emergence; RCI_relative chlorophyll index; DAS_days after sowing; IRGA_system portable infrared gas analyzer; PPFD_density of photon flux; ABef_nutritional indices comprising absorption efficiency; UTef_efficiency of use of nutrients for conversion to dry matter. Introduction Sorghum (Sorghum bicolor) is currently considered to be the fifth most important grain for use as food, fiber production, and energy (Zheng et al., 2011). The crop stands out for presenting satisfactory grain and biomass productivity in regions that are considered unproductive for other cereals because they are very warm and/or dry, with annual precipitation between 375 and 625 mm (Ribas, 2003). In the last decade, total production was 60 million tons in an area of 44 million hectares (Zheng et al., 2011). Sorghum can be cultivated in conditions that are adverse to other crops, however the management strategies aiming reduce the deleterious effect of drying is important to guarantee a suitable production. In this sense, silicon (Si) application can be performed, since it may increase the plant’s tolerance to elevated temperatures (Okamoto, 1969; Soundararajan et al., 2014), hydric deficit (Lux et al., 2002; Hattori et al., 2005), Mg toxicity (Galvez et al., 1987) e Al toxicity (Cocker et al., 1998) and salinity (Kafi and Rahimi, 2011). Silicon is absorbed by sorghum as opaline silicon (phytolites), increasing the growth rates and, therefore, crop production. Moreover, some quality improvements and protection to abiotic and biotic stress have been associated with Si application (Tripathi et al., 2013). When absorbed, Si leads to the formation of a double layer of silica-cuticle and silica-cellulose in the cellular wall, giving to the plants physical resistance and reducing transpiration, resulting in an increase in water use efficiency (Ma and Yamaji, 2006; Barbosa Filho et al., 2001). Silicon accumulation in leaves can reduces the salt accumulation and the plasmatic membranes permeability, maintaining their integrity and functioning through a decrease in lipid peroxidation and an increase in superoxide dismutase activity (Matoh et al., 1986; Zhu et al., AUSTRALIAN JOURNAL OF CROP SCIENCE | SUBMITTED: 16-AUG-2017 | REVISED: 21-OCT-2017 | ACCEPTED: 07-DEC-2017