Irrigation management and hydrosalinity balance in a semi-arid area of themiddle Ebro river basin (Spain)

The analysis of irrigation and drainage management and their effects on the loading of salts is important for the control of on-site and off-site sali nity effects of irrigated agriculture in semi-arid areas. We evaluated the irrigation management and performed the hydrosalinity balance in the D-XI h ydrological basin of the Monegros II system (Aragon, Spain) by measuring or estimating the volume, salt concentration and salt mass in the water input s (irrigation, precipitation and Canal seepage) and outputs (evapotranspira tion and drainage) during the period June 1997-September 1998. This area is irrigated by solid-set sprinklers and center pivots, and corn and alfalfa account for 90% of the 470 ha irrigated land. The soils are low in salts (o nly 10% of the irrigated land is salt-affected), but shallow (<2 m) and imp ervious lutites high in salts (average ECe = 10.8 dS m(-1)) and sodium (ave rage SAR(e) = 20 (meq l(-1))(0.5)) are present in about 30% of the study ar ea. The global irrigation efficiency was high (Seasonal Irrigation Performance Index = 92%), although the precipitation events were not sufficiently incor porated in the scheduling of irrigation and the low irrigation efficiencies (60%) obtained at the: beginning of the: irrigated season could be improve d by minimising the large post-planting irrigation depths given to corn to promote its emergence. The salinity of the irrigation water was low (EC = 0 .36 dS m(-1)), but the drainage waters were saline (EC = 7.5 dS m(-1)) and sodic (SAR = 10.3 (meq l(-1))(0.5)) (average values for the 1998 hydrologic al year) due to the dissolution and transport of the salts present in the l utites. The discharge salt loading was linearly correlated (P < 0.001) with the volume of drainage. The slope of the daily mass of salts in the draina ge waters versus the daily volume of drainage increased at a rate 25% highe r in 1997 (7.6 kg m(-3)) than in 1998 (6.1 kg m(-3)) due to the higher prec ipitation in 1997 and the subsequent rising of the saline watertables in eq uilibrium with the saline lutites. Drainage volumes depended (P < 0.001) on irrigation volumes and were very low (194 mm for the 1998 hydrological yea r), whereas the salt loading was moderate (13.5 Mg ha(-1) for the 1998 hydr ological year) taking into account the vast amount of salts stored within t he lutites. We concluded that the efficient irrigation and the low salinity of the irrigation water in the study area allowed for a reasonable control of the salt loading conveyed by the irrigation return flows without compro mising the salinization of the soil's root-zone. (C) 2001 Elsevier Science B.V. All rights reserved.