Seasonality of the irrigated water quality at the Distrito Irrigado Baixo Acaraú, Ceará, Brazil

Abstract

Seasonality of the irrigated water quality due to rainfall was investigated at Baixo Acaraú Irrigated District (DIBAU), Ceará, Brazil. This study considered the ions, the  Electric Conductivity (EC) and the Sodium Adsorption Ration (SAR). Sample waters were taken monthly from April/03 to Dec./03, except Jun., and each two month from Jan./04 to Sept./05. Water was sampled at Santa Rosa Station, place where water was conducted to the DIBAU. It was analyzed the following parameters: EC, Ca2+, Mg2+, Na+ e K+, Cl-, HCO-3 e SO-24. Besides, the Piper’s triangle and USDA Salinity Lab were used to define water classes. The Wilcoxon test to paired data was applied to identify if there are significant difference among the values of  ion concentrations, EC and SAR  to wet and dry season. Results shown that water does not preset irrigation use limitation in relation to Na+ and Cl- ions. According to USDA Salinity Lab irrigated water presented low to medium salinity risk and low risk of sodicity. Piper’s Diagram indicated that the predominant water class was bicarbonated sodium in both seasons. The Wilcoxon test pointed out significant difference (level of 5%) between the registered values of EC, SAR, Na2+, K+, Mg2+ e HCO3- in wet and dry season.