Épocas de dessecação na qualidade pós-colheita de grãos de soja

Abstract

Desiccation of soybean crops has been used, in some situations, to homogenize maturation, as well as to accelerate the senescence of plants and the natural drying process of the grains, thus enabling mechanized harvesting with reduced losses due to unevenness or due to weather, also reducing the crop cycle. Due to the lack of knowledge or the imminence of unstable climatic periods, which make harvesting impossible, some producers carry out desiccation in stages earlier than recommended (R7), which can lead to qualitative losses in the grains. Thus, it was evaluated the influence of desiccant’s application at different stages of maturation of soybeans on the physiological, physical and chemical qualities of the beans. Experiment area was installed in Embrapa Agrossilvipastoril, Sinop (MT), in 2018/2019 crop, with the cultivars BRS 7980 and M8372 IPRO, in a randomized block design, with four replications. Cultural treatments were carried out as recommended for the culture, but desiccation. For each cultivar evaluated, desiccation occurred in five phenological stages (R5.5, R6, R7.1 R7.3, R8.1), using the desiccant (Paraquat). After mechanized harvesting, beans were dried, cleaned and classified. Then, tests of germination rate, electrical conductivity, apparent specific mass, mass of a thousand grains and components of centesimal composition (crude fiber, ether extract, protein, ash and water) were accomplished. Carbohydrate content was determined by the difference between the grain mass and the sum of the analyzed components. The electrical conductivity to cultivate BRS 7980 showed lower values in stages R6, R7.1 and R7.3, compared to the others. As for the cultivar M8372 IPRO, its results did not differ statistically. Germination rate showed higher values in stages R6 and R7.1 to cultivate BRS 7980 and in stages R6, R7.1 and R7.3 to cultivate M8372 IPRO. For cultivars BRS 7980 and M8372 IPRO, there were a gradual reduction in bulk density and a gradual increase in mass of one thousand grains as the phenological stages advanced. Generally, color only varied in intensity (Cr) for the cultivar BRS 7980 in stages R7.1, R7.3 and R9. For the cultivar BRS 7980, there was no difference between the phenological stages for the content of crude fiber, protein, ash, water and carbohydrates. Ether extract content was lower in the R5.5 stage, in relation to the others evaluated. M8372 IPRO cultivar did not show variation for the contents: ash, water and carbohydrates. Ether extract content, as for the cultivar BRS 7980, was lower at stage 5.5, but it was possible to highlight the stage with the highest content of this component: R8.1. However, the highest protein content was observed at the R6 stage in relation to the other stages.