Three study decades on irrigation performance and salt concentrations and loads in the irrigation return flows of La Violada irrigation district (Spain)

Abstract

Irrigationdistrictsalt balances identify the main sources and sinks of salts and quantify saltloads in irrigationreturnflows. Salt balances were performed in LaVioladaIrrigationDistrict during the 80s (1982–1984), 90s (1995–1998) and 00s (2006–2008) decades. Total Dissolved Solids (TDS) and loads in irrigationreturnflows were related with changes in irrigationperformance and infrastructures during these decades. TDS increased linearly to increases in Irrigation Consumptive Use Coefficient (ICUC) (P < 0.01), and decreased with increases in Drainage Fraction (DRF) (P < 0.001). The salt balances revealed that 82% of the exported salts originated from soil gypsum dissolution. Annual salt yields in returnflows were high and similar in the 80s and 90s (about 19.3 Mg/ha year), and halved in the 00s (9.9 Mg/ha year) due to comparable reductions in irrigation and drainage volumes derived from a better irrigationperformance. Irrigation season salt yields were high and steady around 14.1 Mg/ha for ICUC < 51% and DRF > 66%, and decreased exponentially for values above and below these thresholds, respectively. Therefore, the key management strategy to reduce salt discharge to downstream areas is to decrease drainage volumes by improving irrigation management.