Silício na incidência de pragas e doenças, na qualidade fisiológica de sementes e composição bromatológica do sorgo forrageiro

Abstract

The use of silicon (Si) to increase resistance against different pest species, diseases, and abiotic conditions such as water stress has been widely studied. However, most studies do not address the subsequent stages of crop production, such as the evaluation of seed quality or the nutritional quality of the produced plant material. Bromatological composition and seed quality are influenced by several factors, and different fertilization protocols may alter the characteristics of the seed and the plant as a whole. Given the above, this study aimed to investigate the effect of Si throughout the entire forage sorghum cycle, from increasing resistance to different insect pests and diseases to the physiological quality of the produced seeds and the bromatological composition of the plant material. To evaluate the increase in resistance and the physiological quality of the seeds, two experiments were conducted. One experiment evaluated different doses of Si (0, 300, 600, 900, and 1200 kg ha⁻¹ of Si, plus an additional treatment consisting only of soil correction), while the other experiment evaluated the absence and presence of Si (800 kg ha⁻¹ of Si) in relation to the absence and presence of chemical control, in a two-factor factorial design. The bromatological composition of sorghum was evaluated in the experiment with different Si doses. The experiments were carried out in an experimental field located at Glória Farm, where Si was applied to the soil in the form of calcium and magnesium silicate 30 days before planting. Si content was evaluated in the soil, leaf tissue, and seeds. Assessments of the percentage of plants showing symptoms of insect pest attack (aphids, caterpillars, and stink bugs) were performed at 23, 42, 49, and 56 days after crop emergence (DAE). Parameters related to production, such as yield and thousand-seed weight, were evaluated, in addition to the physical and physiological quality of the seeds through water content, germination, electrical conductivity, emergence, emergence speed index, mean emergence time, seedling dry mass, and accelerated aging. Bromatological analyses included the determination of ash, ether extract (lipids), crude protein, and neutral detergent fiber (NDF) and acid detergent fiber (ADF). There was an increase in Si content in the soil and leaf tissue with increasing silicate doses applied to the soil in both experiments; however, no difference was observed in the Si content of sorghum seeds. Si increased sorghum resistance to attacks by stink bugs of the genus Diceraeus Spinola in the first experiment and by Diceraeus spp. and caterpillars of Spodoptera frugiperda (Smith) in the second experiment, reducing the percentage of plants showing symptoms. The different silicate doses applied did not influence the production or physiological quality of sorghum seeds. The use of chemical control resulted in a slight increase in root dry mass regardless of Si use; however, chemical control had no effect on insect populations, seed production, or seed quality. Regarding bromatological composition, no effect of Si was observed on the percentages of ash, ether extract, crude protein, or NDF. When compared to the additional treatment, in which Si was not applied and lower amounts of Ca and Mg were supplied, an increase in ash content was observed at the dose of 900 kg ha⁻¹ and an increase in ADF at the dose of 1200 kg ha⁻¹. The reduction in insect attack, whether through the use of Si or chemical control, did not interfere with seed quality, and high doses of Si, Ca, and Mg in the soil may reduce the digestibility of forage sorghum. The benefits of Si in pest control outweigh the possible disadvantages related to forage sorghum digestibility, without affecting crop yield or seed quality.