EFFICIENCY OF FOLIAR SULFUR SUPPLY TO SOYBEAN IN DIFFERENT DEVELOPMENTAL STAGES

173 A matéria publicada nesse periódico é licenciada sob forma de uma Licença Creative Commons – Atribuição 4.0 Internacional http://creativecommons.org/licenses/by/4.0/ EFFICIENCY OF FOLIAR SULFUR SUPPLY TO SOYBEAN IN DIFFERENT DEVELOPMENTAL STAGES Ivan Vilela Andrade Fiorini, Cassiano Spaziani Pereira, Helcio Duarte Pereira, Luiz Gustavo Balbinot, Gabriel Wiest, Mateus Emanuel Schoffen Universidade Federal de Lavras , Lavras-MG, Brasil 2Universidade Federal do Mato Grosso, Sinop-MT, Brasil 3Universidade Federal de Viçosa, Viçosa-MG, Brasil


Introduction
The soybean (Glycine max) is a crop of world agricultural importance. In 2019 the USA had the greater mean yield of the grain in the world, with about 3,468 kg ha -1 , followed by Brazil with mean of 3,201 kg ha -1 . The Mato Grosso state is the major soybean producer in the country. In the 18/19 crop the state production reached 32,454.5 millions of tons, in a total area of 9,699.5 millions of hectares, but despite the large soybean production in Mato Grosso the yield is at levels below the national mean, with 3,120 kg ha -1 [1].
One of the factors influencing the soybean yield is the deficiency of some essential nutrients, like the sulfur, which is the fourth main nutrient required by the crop. The need of sulfur in mineral nutrition of plants is already known for much time, mainly due to its participation in enzymes and protein formation. In general, soils cultivated for many years with continuous usage of concentrated fertilizers, hence with low levels of sulfur, end up generating deficiency of this element on the agricultural crops, mainly in the Cerrados region of Brazil [2].
The sulfur deficiency in Brazilian soils is influenced by several factors, the low fertility, added to the low levels of organic matter, the increase in nutrient exportation due to high yields and the high sulfate leaching are the main causes. Richart et al. [3] did not observe increase in sulfur levels in the layer of 0 to 10 cm depth after applications until 60 kg ha -1 of sulfur and attribute this fact to the facility of removing sulfate ion on the soil profile. The authors still highlight more attention should be given to sulfur in order to it does not become limiting to the crops, mainly in soils with low levels of organic matter. In this way, the adequate sulfur level in the soil is a factor determining the growth and yield of crops. Soils deficient in sulfur generate grains of lower quality, especially in terms of protein formation, besides take the plant more vulnerable to diseases and abiotic stress [4][5][6].
Currently, the soil supply of nutrients is one of the main practices that ensure higher yield levels of the crops. However, the application of nutrients via soil is one of the more costly practices in the cost of agricultural products, due to price volatility and its impacts on the profit of the crops. The sulfur absorption occur on the sulfate form S-SO4 2-, it can also be absorbed as organic (S), SO2 (air) and wettable S (pesticides) via foliar. On the plant it presents itself on the organic form on the majority (cystine, cysteine, methionine, protein, glycosides and vitamins). It is found on the literature works associating the sulfur assimilation with the nitrogen assimilation, being one correlated with the other and with the levels of chlorophyll in leaves and grain yield [7,8]. agronomists and farmers still consider the sulfur as a secondary element [9]. The sulfur is, probably, the macronutrient less employed on fertilizations and little studied [10]. of the element in the soil-plant system to understand the real necessity and importance of sulfur on the agricultural productivity.
That said, the objective of the work was to determine the effect of sulfur usage, about vegetative characteristics and yield components, by foliar application in different stages of soybean development.

Material and Methods
The experiment was carried out in commercial area, cultivated in minimum tillage system for five years, between 2018 October and 2019 January, on Sinop-MT city. soil is classified as red yellow latosol [13]. hours.
The data was submitted to analysis of variance (ANOVA) at the level of 5% probability, by the F test, with the help of SISVAR statistical software [15]. The means were compared by the Scott-Knott test at 5% probability.

Results and Discussion
The characteristics evaluated at the flowering stage,  Corroborating the results found here, Tiecher et al. [19] also did not verify significant increases in shoot dry mass of the crops as soybean, sorghum, sunflower, millet and mammon with Unlike the present work, such authors found increases in shoot dry mass of 29% with sulfur application of 30 kg ha -1 .
For the individual effects compounding the grain yield, as the number of pods, number of grain per pod and thousand grain weight, and also for grain yield itself, did not verify significant differences in function of times of sulfur application (Table 3).
There were significant effects for the interaction between doses of sulfur and times of application (stages) for thousand grain weight and grain yield.   Unfolding the interaction between sulfur doses applied within times of application, for thousand grain weight, verified that on the V2 stage the largest thousand grain weight was obtained with the dose of 750 mL ha -1 . Such fact did not happen on the stages V2+10 and V2+20 days (flowering), which effect of doses within time of application did not differ (Table 5).