Salt accumulation in soils and plants under reclaimed water irrigation in urban parks of Madrid (Spain)

Reclaimed water irrigation in urban parks is expanding all over the world and could cause salt accumulation in soil and plants. Since the beginning of the 2000s, the city of Madrid (Spain) has been using reclaimed water to irrigate its parks. The main aim of this study was to estimate salt accumulation in soils and plants due to reclaimed water irrigation in two urban parks of Madrid. It was conducted over five consecutive years and the chemical properties in soil solution, soil and plant leaves of four species were analyzed. Two plots from each park were selected, one irrigated with reclaimed water (RW) and another one irrigated with drinking water (DW). There was a steady increase of Cl-, Na+, SAR and electrical conductivity (EC) in soils that were RW irrigated for 5 years, while in DW plots lower values for these parameters were observed. Likewise, there was no soil sodification in RW plots. On the contrary, the park which has been RW irrigated for 15 years showed a slight soil salinization (EC > 2 dS m(-1)). There were significant differences for the Cl and Na (%) leaf content between species irrigated with RW versus DW. Overall, salt concentration in leaves was similar to the values found in the literature, being in most of the cases below the threshold when plants start to show injuries. However, an adequate leaching requirement (9%) is advisable in order to wash out the excessive salt accumulation in parks irrigated with reclaimed water.