Irrigation water quality in Alentejo (Portugal) study of the irrigation perimeter of the reservoir of Roxo

Abstract

Alentejo is a region of Portugal located in the south of the country and the main economic activity is agriculture. In Alentejo the precipitation is very irregular. The problem of droughts often occurs. The Alqueva reservoir is the biggest reservoir in Europe and provides water for more than 120,000 hectares for agriculture. Before the use of the reservoir, the main agricultural products were cereals. Now farmers grow vegetables and they make an intensive culture of olive trees and almond trees. The Roxo reservoir is one of those will receive water from Alqueva in 2016. The increase of water in quantitative and qualitative terms can provide very significant increases in the growth of the soil production that we must monetize in the best way. The aim of this study was evaluate the quality of water resulting from the monitoring carried out during 2014/2015 in the hydraulic system and in the drainage network of the irrigation perimeter of Roxo's reservoir to be made a more sustainable management of irrigated area. The main conclusions were as follows: i) the water of the irrigation channel and drainage network show a mil to moderate degree of salinity risk; ii) doesn t show characteristics to modify the soil infiltration conditions; iii) indicates degree of restriction slight to moderate due to the amounts of Na+ and Cl-; iv) the drainage network presents toxicity due the chlorides and boron; v) the ammonia nitrogen and nitrate values were low. The application of nitrogenous fertilizers seems to influence the results.