Effect of application of flowering inhibitor on sweet sorghum

Studies on sweet sorghum have been conducted in countries like Brazil, USA, India and Argentina to complement ethanol production. In Brazil, it is cultivated in areas for sugarcane renovation, and can be used in sugarcane industries. However, the use of chemical flowering inhibitor can increase sucrose in stalks, resulting in higher production. Therefore, the goal of the present study is to evaluate the effect of Etefom application on two sweet sorghum hybrids. The experiment was carried out with cultivation in “D” productive environment, using the Nexsteppe J53 and Embrapa BRS511 hybrids of sweet sorghum. Application of the flowering inhibitor was done 70 days after sowing. From the beginning to the end of the experiment, the plants’ development was evaluated according to their biometric aspects: height, diameter of the stalk, moisture, tons of stalks per hectare (TSH), tons of dry matter per hectare (TDM), Brix, liters of juice per hectare and liters of ethanol per hectare. Results of flowering inhibitor application in sweet sorghum are dependent on the hybrid used, with a higher response to J53 between 90 and 110 days after sowing.


INTRODUCTION
The sugarcane sector has been gaining prominence in the Brazilian economy, with an approximate growth of 65% in the sector in the last ten years.There is a prediction that in 2017/2018 harvest, 647 million tons of sugarcane will be produced, in detriment to the 431 million processed in 2005/2006(CONAB, 2017)).
Ethanol and energy are responsible for the production of sugar, and the sector already shows signs of insufficiency in meeting a higher demand, since there is a growing increase in the automotive industry.In 2015, there was an increase from 40 to 50 million of flex-fuel vehicles (UNICADATA, 2017).
In this sense, there is a search for new technologies that can increase the annual production of ethanol in the country, without increasing the production costs and the planted area (Jaiswal et al., 2017), and also, the use of new raw materials that can be grown in sugarcane renovation areas during off-season (Barcelos et al., 2016;Santos et al., 2015).
Among these, sweet sorghum stands out, with a vegetative cycle of 90 to 120 days, yield of 40 to 60 t/ha, mechanized planting and harvest, the possibility of using agroindustrial infrastructure present in the sugarcane industries, high sugar concentrations in the stalks (Masson et al., 2015) and production of up to 3000 L of ethanol per hectare (Almodares and Hagi, 2009).However, the useful period of industrialization of this raw material is short, maximum of 30 days, making agroindustrial planning difficult, considering that the harvest can occur in a period in which there are still considerable precipitation indexes in the country.After this period, much of the sucrose stored in the stalks is translocated to the panicles, and stored as starch, with a marked decrease in the amount of juice (Freita et al., 2015).
In this way, there is search for alternatives that can increase harvest and enable adequate management of the crop in off season.Among these, the use of flowering inhibitors, which prevent the formation of panicle, resulting in no displacement of the sucrose from the stalk to the tassel, can be highlighted (Blanco et al., 2017).
Thus, the aim of this study is to evaluate the effects of flowering inhibitor application on sorghum culture.

MATERIALS AND METHODS
The experiment was conducted at the experimental farm of the Universidade Sagrado Coração (USC) located in the municipality of Agudos in the State of São Paulo in 2017/2018 harvest season.The soil of the area is yellow dystrophic Oxisol, the region climate is classified as Cwa subtropical climate, according to Köeppen, and is classified as "D" productive environment.The farm is located at latitude 22.283°S and longitude of 48.980°W with average altitude of 530 m.The experimental area is 400 m 2 , with 6 plots of 33 m 2 each, being previously subjected to pH correction (90 days before planting), elimination of weeds, plough and harrowing.
The Nexsteppe J53 and Embrapa BRS511 sweet sorghum hybrids were used.The sowing was carried out on 07 January 2017, using a 3-row seeder, with a rate of 5 to 6 seeds per meter, and 0.5 m spacing between lines.20 days after sowing (DAS), manual thinning was performed to adjust the final stand of the crop to 110.000 plants per hectare.
The experimental design used was subdivided plots with two treatments and three repetitions.The primary treatments were constituted by the application or not of flowering inhibitor, while sampling times constituted the secondary treatments.Each sorghum hybrid was evaluated separately.The results were subjected to analysis of variance by F test and the averages compared by the Tukey test (5%), using the Agroestat program (Barbosa and Maldonado Junior, 2017).

RESULTS
Figure 1 shows the average values observed for stalk height of the BRS511 and J53 sweet sorghum hybrids subjected to flowering inhibitor application.For the BRS511 hybrid, the growth stopped at 75DAS, whereas for J53, the growth paralysis only occurred at 90 DAS.Considering the inhibitor application, this input decreased plant height values.Figure 2 shows the values obtained for the stalk diameter of the BRS511 and J53 sweet sorghum hybrids.
The stalk diameter of the BRS511 variety showed a decrease in values after 90DAS, with little difference between the inhibitor treatments.The J53 variety, when subjected to the flowering inhibitor at 75 DAS, interrupted its growth.The BRS511 variety showed greater diameter   variance from sowing to maturation. Figure 3 shows the values determined for the Brix percentage of the BRS511 and J53 sweet sorghum hybrids.The BRS511 variety showed a percentage of Brix in the control treatment similar to the one with the inhibitor.The J53 variety had the highest percentage of Brix in the sample where the chemical flowering inhibitor was inserted at 110 DAS.
Figure 4 shows data for the number of tons of stalks per hectare for each hybrid, with and without the use of the flowering inhibitor.The BRS511 cultivar presented increasing numbers until 75 DAS; when the inhibitor was applied, the  numbers reduced and at the end of the cycle, they increased again.The J53 variety presented lower results after application of the chemical flowering inhibitor; however, it did not differ significantly from the sample without treatment.The data for dry matter quantity produced per hectare of the sweet sorghum hybrids subjected to the application of chemical flowering inhibitor are shown in Figure 5.For the BRS511 and J53 varieties, the inhibitor treatments presented better conditions for the dry matter production, especially the J53 variety.
Considering the volume of juice obtained per hectare (Figure 6), there was a decrease in this parameter after 75 DAS and increment at the end of the plant cycle for both hybrids and treatments (with and in inhibitor).Figure 7 shows the values of ethanol obtained per hectare for each hybrid of cultivated sweet sorghum subjected to treatment with chemical inhibitor.
The highest values were obtained for J53 hybrid at 110DAS, with application of flowering inhibitor.From 90 DAS, the application of this input in this hybrid resulted in larger quantities of ethanol produced in relation to the control.However, the flowering inhibitor did not result in positive reflections for the BRS511 hybrid, which presented an average of 20% less ethanol produced per hectare of the plant.

DISCUSSION
Considering the physiology of sweet sorghum, it is expected that it will grow until panicle emission, stage where the plant directs metabolites to produce and fill the grains (Borém et al., 2014).This behavior was observed in this study.However, in hybrids that were subjected to Etefom application, the height was lower as compared to the control treatment.It probably occurred because the Etefom stopped the stalks growth, but in the control, the growth of panicle occurred, resulting in increase in height.
The values for height are lower than those obtained by Abascal et al. (2014), who studied the biometry of two hybrids of sorghum cultivated in the region of Jaboticabal-SP and determined values were about 3 m at 130 DAS.The soil of that region is considered "Terra Roxa", "A" environment, while the soil of the research was in sandy "D" environment.Although, the application of flowering inhibitor changed the height, the diameter was not affected by this treatment, for Malibu J53 and BRS511.However, it should be highlighted that in 90 days, this parameter decreased for all treatments.It is expected, because plant losses moisture (Borém et al., 2014).In media, the diameter of stalks were 2 cm, values similar to that obtained by Abascal et al. (2014) and Tsuchihashi and Goto (2004), which determined diameters of 1.70 cm.
The Brix was influenced by Etefom only for hybrid J53, in 110 DAS, stage that showed an increase of this parameter.This result is motivating since the sugars of the plant were not translocated to the panicle during the flowering period.Viana et al. (2017) observed that Etefom increase in 1% Brix of sweet sorghum hybrids BRS508 and BRS509, at 110 DAS, as compared to the control treatment.Therefore, it can be inferred that the Etefom results in different behavior for hybrids.In media, the Brix was 19%, values higher than that obtained by Silva et al. (2016) who found 16.6 for the BRS508 hybrid.Freita et al. (2014), studying the genotypes, CVSW80007 and CVSW80147 determined 18% at 130 DAS.The J53 variety cultivated in the same soil of this research, presented 17.8°Brix at the end of its cycle, as pointed out by Nogueira et al. (2017).Other fact observed was the non-influence of Etefom in TSH.It is important because the goal of this product is only to increase the sugar content of stalk, and increase the harvest period (Viana et al., 2017).However, data from Jardim et al. (2016) indicate that the BRS511 variety can reach up to 69.7 t/ha at the end of its cycle when cultivated in "A" environment soils.The J53 variety, when subjected to cultivation in the same environment in which the research was carried out, can present up to 33 t/ha, as reported by Nogueira et al. (2017).
Although, the Etefom did not affect the TSH, it showed increase of TDM for J53 with flowering inhibitor application.This makes the production of biomass to become interesting.The J53 variety can present up to 11.12 t/ha at the end of its cycle, as pointed out by Nogueira et al. (2017).The greater the dry mass of the plant, the more bagasse the agroindustrial unit will generate, benefiting the energy production.Thus, the inhibitor can also aid in the energetic gain of the factory.Considering that, the juice volume per hectare did not show differences between treatments.It is interesting, because the inhibitor did not promote drying of the stalk.However, this behavior is detected as time goes by.This occurs in function of the senescence stage of sweet sorghum that occurs after the period of panicle emission (Taiz and Zeiger, 2004).These results are similar to those obtained by Gonçalves et al. (2016), who studied the BRS511 hybrid, and determined the production of 33290 L/ha of extracted juice.
The most important information of this study is the increase of 500 L of ethanol produced per area when Etefom is used in hybrid J53, at 110 days.It is interesting, because it promoted the production of 3000 L of this fuel per area, and Almodares and Hadi (2009) obtained the maximum potential of this raw material.Besides that, this value is similar to that obtained for sugarcane producers in Brazil (CONAB, 2017).Considering that the renovation area at 2017 was 12% of the total (CONAB, 2017), it will increase the ethanol production in this country to 3.5 billion liters.Other point to discuss is that the hybrids of sweet sorghum present a different behavior from the flowering inhibitor, and may even differ in relation to the dosage to be applied.Thus, future studies with different doses of Etefom for BRS511 hybrid may demonstrate different behavior.

Conclusion
The results of the flowering inhibitor application in sweet sorghum are dependent on the hybrid used, with a higher response to J53 between 90 and 110 days after sowing.

Figure 1 .
Figure 1.Average values obtained for the height of sweet sorghum stalks, subjected to the application of flowering inhibitor, for BRS511 and J53 hybrids, 2017/2018 Harvest, Bauru-SP.

Figure 2 .
Figure 2. Average values obtained for the diameter of sweet sorghum stalks, subjected to the application of flowering inhibitor, for BRS511 and J53 hybrids, 2017/2018 Harvest Bauru-SP.

Figure 3 .
Figure 3. Values obtained for the percentage of Brix in sweet sorghum, subjected to the application of flowering inhibitor, for BRS511 and J53 hybrids, 2017/2018 Harvest, Bauru-SP.

Figure 4 .
Figure 4. Values obtained for tons of stalks per hectare of sweet sorghum hybrids of BRS511 and J53, subjected to the application of chemical flowering inhibitor, 2017/2018 Harvest, Bauru-SP.

Figure 5 .
Figure 5. Data obtained for the amount of dry matter content per hectare of BRS511 and J53 sweet sorghum hybrids subjected to the application of chemical flowering inhibitor, 2017/2018 harvest, Bauru-SP.

Figure 6 .
Figure 6.Data obtained for the juice volume of BRS511 and J53 sweet sorghum hybrids subjected to the application of chemical flowering inhibitor, 2017/2018 harvest, Bauru-SP.

Figure 7 .
Figure 7. Data obtained for the production of ethanol per hectare of BRS511 and J53 sweet sorghum hybrids subjected to the application of chemical flowering inhibitor, 2017/2018 harvest, Bauru-SP.