The Effect of Vinasse Application in Lowland Areas Cultivated with Sugarcane on Spatiotemporal Variability of Groundwater Salinity in the Northeast of Brazil

Abstract

Aims: The aim of this study was to evaluate the spatiotemporal variability of electrical conductivity in groundwater under vinasse application on a lowland area cultivated with sugarcane in the northeast of Brazil. Place and Duration of Study: This area is located in a sugarcane/ethanol plant in Pernambuco state (Brazil) and receives an average annual rainfall of 2100 mm, between January 2011 and August 2011. Methodology: The experiment was composed of 54 georeferenced wells spread over an area of five hectares of sugarcane crop. This sampling was carried out six times from the 54 wells during eight months to evaluate the temporal variability of electrical conductivity (EC) in the groundwater. Descriptive statistics and geostatistical methods were used for spatial modeling and to create maps. A correlation matrix using Spearman’s method was calculated by SAS to evaluate if there was a temporal correlation among the electrical conductivity values of groundwater over a long period of time. Results: The mean EC does not present any risk of soil salinization, and do not produce a limit for irrigation. All data had normal frequency distributions. A Gaussian model was adjusted for all samplings. The range of spatial dependence was from 20.43 m 4th sampling) to 34.64 m (before vinasse application), with an average of 25.17 m. EC values in the groundwater during the monitoring period were not high enough to indicate a severe degree of restriction on use, i.e. < 3dS.m-1. Conclusion: Groundwater electrical conductivity was reduced by rainfall events and did not present a risk of salinization. The range of spatial dependence values demonstrated that it was necessary to use 32 m spacing between observing wells for the sustainable management of vinasse in lowland areas.