International Journal of Environmental & Agriculture Research (IJOEAR) ISSN:[2454-1850] [Vol-2, Issue-6, June- 2016] Page | 45 Physiological Assessments of Sweet Sorghum Inoculated with Azospirillumbrasilense according to Nitrogen Fertilization and Plant Growth Regulators Cleber Junior Jadoski 1 , João Domingos Rodrigues 2 , Denilson de Oliveira Guilherme 3 , Elizabeth Orika Ono 4 , Rúbia Renata Marques 5 , Sidnei Osmar Jadoski 6 1,3,5 Departament of Agronomy, Dom BoscoCatholic University, Campo Grande, Mato Grosso do Sul, Brazil. 2,3 Departament of Botany, University of State of São Paulo, Botucatu, São Paulo, Brazil 6 Departament of Agronomy, University of State of Centro Oeste, Guarapuava, Paraná, Brazil Abstract—Some factors, such as yield increase and production cost reduction, must still be assessed as a way toimprove the sweet sorghum success prospects. The use of plant growth regulator mixtures has shown significant results in crop yield.Nitrogen assimilation stands out as one of the main limiting factors in plant production. Given the physiological effects of plant growth regulators and their mode of action in the photosynthetic metabolism, the aim of the current study is to assess the physiological responses of sweet sorghum plants inoculated with Azospirillum brasilenseto the use of nitrogen fertilization and plant growth regulators. The experiment comprised split plots, with four repetitions. The treatments comprised nitrogen (0, 40, 80, 120 and 160 kg ha -1 ) and biostimulant levels (0, 300, 400, 500 and 600 mL ha -1 ) in sweet sorghum culture inoculated with Azospirillum brasilense. Variables such as gas exchange and total recoverable sugars (TRS%) were assessed. The application of plant growth regulator at the dose 440.7 ml ha-1 showed the highest photosynthetic efficiency up to 46 DAE. According to the experimental conditions, the plant growth regulator treatment had no effect on the TRS %. It is concluded that the plant growth regulator did not affect the production of sugars by the plant. Keywords— total sugars, kinetin, photosynthesis, inoculation I. INTRODUCTION Sweet sorghum (Sorghum bicolor Moench) is the name given to the sorghum plant able to produce and accumulate sucrose in the stem, reaching amounts close to those of the sugarcane. The sorghum belongs to the family Poaceae. It is believed that its center of origin lies on the region where Sudan and Ethiopia are located in the African continent and that; apparently, it was disseminated worldwide by the native Africans who were smuggled into slavery. Nowadays, it is grown in most tropical and subtropical regions and is the fifth most produced cereal worldwide (MOREIRA, 2011). Sorghum is considered a positive energy balance culture and stands out as a promising raw material to generate bioenergy, due to its high fermentable fiber and sugar contents, which may be exploited on a large scale and with great adaptability to different weather and soil conditions (SANTOS et al., 2014).In addition, the short production cycle (six months for high biomass yield) and the low water demand, in comparison to that of the sugarcane and corn, favor the sorghum, which shows better energy efficiency (NAGAIAH et al., 2012; SERNA-SALDÍVAR et al., 2012). In addition to the sucrose production by sorghum, it can be said that some factors, such as productivity increase and crop production cost reduction, are still to be assessed as a way to improve the sweet sorghum success prospects. Among such factors, the high cost of fertilizers is a bottleneck that narrows the cost/benefit ratio in the sweet sorghum cultivation and in the sugar and alcohol generation (MOURA et al., 2005). Although nitrogen is abundant in the atmosphere, the plants metabolize it just in its nitric and ammonia forms. Nitrogen fertilizers are expensive, and the biosphere reserve comes from the atmosphere.It cannot be directly assimilated by plants in its molecular form; however, the biological N fixation processes by prokaryotic organisms make such assimilation possible. The proliferation of soil bacteria adhered to the plant root surface was discovered in the early nineteenth century, along with the discovery of nitrogen fixation (MOREIRA, 2007). Thus, the use of nitrogen-fixing bacteria benefited the yield of several crops such as soybean (Glicine max (L.) Merrill). Therefore, whenever nitrogen-fixing bacteria are inoculated in seeds, there is potential release nitrogen of approximately 150