The impact of irrigation over soil-water resources

Abstract

The aim of this work was to identify the influence of irrigation management and climatic conditions over the soil water content, salinity, sodium adsorption ratio (SAR) in the soil profile, and variation of the water table level at the Irrigation District of Baixo Acaraú, Ceará, Brazil. Soil samples were collected in two different sites, one irrigated and another one a rain fed field. Soils samples were taken for each 0.50 m depth until  the water table (7 m) was reached, during rainy and irrigation seasons. The groundwater table was measured, monthly, from December 2003 to November 2005, on November 2006, on March and May 2007, in four shallow wells, two located in irrigated fields and two on rain fed areas.  According to the results, the lowest values of Electric Conductivity (EC) and SAR were always registered in irrigated field (S2), due to the sandy soil texture through the total profile. Soil water content, through the studied profile (7 m), was lower during the rainfall season than in the irrigation period. The difference in water content (irrigated season – rainfall season) was statistically significant (<1%) by Wilcoxon test. The water table level rose 2.5 m and depleted 0.15 m for wells P1 and P2, respectively, located in irrigated fields, while those located in rain fed fields, P3 and P4, presented a depletion of 3.7 and 1.7 meters, respectively. Therefore, water table should be monitored in relation to the water level, salt addition, organic matter, fertilizers and pesticides residues.