Monitoramento do lençol freático em área de várzea sob fertirrigação com vinhaça em cana-de-açúcar

Abstract

Sugarcane is cultivated in Brazil in an approximate 8-million hectare area, condition that places the country as the first in the world concerning the areas cultivated with that kind of culture. With the growing demand for ethanol in the market every crop, its greatest production implied in the growth of the vinasse generation. That sub-product is largely utilized in agricultural practices such as fertilizers. However, the vinasse might cause environmental impacts when not managed properly, damaging the aquatic fauna and water bodies as well as compromising the health of the population. The present work aims at evaluating the effects of the vinasse utilization on the sugarcane fertirrigation in floodplain areas. It was conducted at Engenho Aldeia, which belongs to Usina Cucaú, in Rio Formoso, Pernambuco. The experimental gadget adopted was formed of a 81-monitoring wells georeferenced mesh, distributed along a 7.5 hectare area, constituting three 2.5 hectare subareas, all vegetated with sugarcane. The monitoring wells were distributed in two molds in each of the three subareas, being 15 wells in the area submitted to the vinasse application, and 12 wells on the edges totalizing 27 wells. The distance between the wells is 30 x 30 m on the edge area and 15 x 30m on the areas submitted to the vinasse application. Six water collections from the water table were performed: one before the vinasse application, and five after it, over different periods, with the objective of monitoring the concentration on the elements throughout time. Seven K+, Na+, Ca2+, Mg2+, CE, pH and SAR quality parameters were analyzed over time, highlighting potassium for appearing in higher concentration in vinasse, and SAR for indicating the water and soil salinity. The sugarcane itself (TCH) and sugar production per hectare (TPH) were defined as production components, whilst the apparent content of the soluble solids in the sugarcane juice (ºBrix), the sugarcane polarization (PC) and the total recoverable sugar (ATR) were evaluated for technological quality. Modifications in the sugarcane technological quality were not observed. No changes in the technological quality of sugar cane. Vinasse provide 9% productivity stems and 4% at sugar yield. The sodium absorption ratio showed that there is no risk of salinity in the area during the evaluation period. Results also show that concentration chemical elements reduced and are related to fluctuations of groundwater levels in the aquifer and rainfall. Finally, vinasse can be applied in floodplain areas annually where high rainfall is.