Irrigation management, nitrogen fertilization and nitrogen losses in the return flows of La Violada irrigation district (Spain)

35 Pags., 5 Figs., 5 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/01678809Nitrogen (N) pollution induced by irrigated agriculture is a significant environmental problem. The main N inputs and outputs were measured or estimated in the semi-arid LaVioladairrigation district (Spain). Data on two periods (1995–1998 and 2006–2008) were compared and related to observed changes during the decade in cropping patterns and N fertilization and irrigationmanagement. N fertilization exceeded crop N uptake due to over-fertilization of corn (426 kg N/ha in 1995–1998 and 332 kg N/ha in 2006–2008) and alfalfa (62 kg N/ha). Between the two periods, N fertilization decreased by 56%, primarily due to a change from corn to alfalfa and barley. Accordingly, N losses in the irrigationreturnflows (IRF) diminished from 31% of the applied fertilizer in 1995–1998 to 20% in 2006–2008. NO3− concentrations and NO3-N loads in the IRF decreased from 40 mg/L and 106 kg N/ha in 1995–1998 to 21 mg/L and 22 kg N/ha in 2006–2008, due to lower N fertilization, lower corn area and improved irrigation efficiency. N contamination in the IRF will be minimized by increasing the irrigation efficiency and decreasing the corn area and its N fertilization rates, particularly when supplemental organic N is applied at pre-sowing.This work was sponsored by the Spanish Ministry of Science and Education project AGL2006-11860/AGR, the European Regional Development Fund (FEDER) and the European Union project INCO CT-2005-015031.Peer reviewe