USE OF RECLAIMED WATER AND REGULATED DEFICIT IRRIGATION: AN ALTERNATIVE TO MEDITERRANEAN CITRUS

摘要

The use of reclaimed wastewater is expanding all over the world, because it helps to preserve the supply of potable water for human consumption by providing an alternative source of water for irrigation and other uses. Agriculture still is a very important economic sector in many European countries, and represents the highest consumptive water use. The effect of RDI and different water quality were investigated in a commercial mandarin orchard during three growing seasons. Six irrigation treatments were differentiated, an irrigation control treatment (C, 100% ETc) and a regulated deficit irrigation (RDI, 50% ETc during stage II of fruit growth) were applied using three different water quality sources [freshwater (EC ≤ 1),irrigators association water (1≤EC≤4) and reclaimed water (EC ≥ 3)]. Reclaimed water presented different mineral composition. Macro and micro nutrients were higher, especially potassium. The phytotoxic elements, B, Na and chlorides were higher in reclaimed water. The soil water content was maintained at field capacity for all treatments from the beginning of the irrigation season till the start of deficit irrigation; since that date till the end of deficit irrigation the soil water content of the RDI treatments were depleted progressively by root water uptake while only 50% of the water lost by ETc were restored to the soil. The effects of different types of water were not evident on the seasonal evolution of soil water content. In 2009,in the deficit irrigation period, a significant increase in the SWS of treatments irrigated with reclaimed water was observed due to the osmotic effect arising from salt accumulation in rootzone. In soil salinity, A tendency was identified in terms of salts accumulation in the soil in reclaimed water treatments. A reduction of stem water potential was observed in the regulated deficit irrigation treatments respect to the values observed in control plants, independently of the quality of water applied. The stomata conductance and the assimilation rate were reduced during the water deficit period when reclaimed water was used, but without significance differences.