The nitrogen role in vegetables irrigated with treated municipal wastewater
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The reuse of treated municipal wastewater for irrigation is an established alternative to conventional water, in many countries of the world, particularly where or when water resources are extremely limited. Wastewater reuse could represent a double benefit when used in agriculture, helping overcome any lack of water resources and additionally, enriching the soil with nutrients - especially nitrogen and phosphorus. In the experimental site of Castellana Grotte (Apulia region, Southern Italy) during the 2012/13 and 2013/14 growing seasons, vegetable crops (fennel and lettuce) in succession were dripirrigated with three different water sources. Two reclaimed water streams, obtained by applying different treatment schemes to the same municipal wastewater (an effluent from the full-scale treatment plant and an effluent from the Integrated Fixed-film Activated Sludge – Membrane BioReactor pilot plant) and a conventional source, to verify the crops response and nutrient contribution through wastewater supply. Both lettuce and fennel yields were enhanced by the high content of nutrients in the effluent of one of the treatment plants, which had been operated for partial nitrogen removal. For Fennel 2013/14, wastewater-reuse led to a 54% reduction of nitrogen supply in relation to the other plots normally fertilized. In this way, an estimated saving of about 98.00 € ha-1 was achieved. Crops irrigated with treated wastewater operated for partial nitrogen removal (IMBR) showed early ripening (8 days for lettuce and 35 days for fennel 2013/14) and better quality than others not similarly-treated. However, the wastewater presented a nitrate content in excess of legal limits (35 mg L -1 , D.M. 185/2003). Therefore, the contribution of nutrients increased production (47 vs 32 t ha-1 in IMBR and WELL 2012/13 fennel theses, 53 vs 31 t ha-1 in IMBR and WELL 2013 lettuce theses and 40 vs 31 t ha-1 in IMBR and WELL 2013/14 fennel theses respectively) and improved product quality, while simultaneously saving money for chemical fertilizers not supplied, producing less environmental impact.