Efeito da fertirrigação com vinhaça no desenvolvimento inicial da cana-de-açúcar, na condutividade e teor de potássio no solo

Abstract

Using vinasse as a source of potassium for sugarcane is important to save the use of fertilizers and an appropriate destination for that residue of sugarcane production. Despite this, its use in periods of low potassium extraction can compromise the initial development of the crop due to the increase in soil salinity. Potassium leaching can also occur, contaminating the soil and groundwater. This study aimed to evaluate the effect of localized vinasse application on the initial development of sugarcane, soil salinity, and potassium leaching. An experiment was conducted in two areas with different soil textures, the first at Santa Rita Farm (SR), Pirassununga - SP, on sandy soil, and the second one at Batatais Farm (BT), Batatais - SP, on clayey soil. The experiment was carried out in different periods for each area, looking for extreme soil water availability for the crop. In SR, the field trial was carried out in a period of low rainfall; in BT, in a period of high rainfall. We measured soil and plant parameters to analyze the results: for the soil, electrical conductivity (0-40 cm), and potassium content (0-40 cm and 75-85 cm); for the crop's early development, the number of tillers and the fresh matter weight. Soil samples were collected in three different periods, depending on the date of application of the treatments (1 day before, 1 day after, and 30 days after), namely: (i) localized application of vinasse (Vlocal); (2) application of vinasse in the total area (Vtotal); (3) application of localized water (W); and (3) control (T). To evaluate the potassium leaching, samples were collected in the soil layer of 75-85 cm, 75 days after the application of the treatments. In the SR, there was an increase in electrical conductivity and potassium content in the layers 0 to 40 cm, and this increase was maintained after 30 days of application of the treatments. In this area, there was a reduction in the amount of tiller and green mass in the Vlocal. In BT, there was an increase in salinity in layer 0 to 40 cm one day after the application of the treatments, but after 30 days, the salinity no longer showed any difference in layer 0 to 20 cm. In this area, no significant difference was observed in the initial development of sugarcane in any treatment. There was no leaching of potassium to the layer 75 to 85 cm in any treatment of the two areas. It is concluded that the localized application of vinasse can increase the salinity in the soil layer, where the root system of the sugarcane develops in its initial development. This increase in salinity for a period longer than 30 days was enough to reduce the initial development of the crop. The non-application of potassium did not affect the initial development of sugarcane in any of the areas. The localized application of vinasse in the evaluated environments did not present a risk of leaching, but further studies are recommended in sites with sandy-textured soil and high rainfall.