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Cavero J.,CSIC - Aula Dei Experimental Station | Barros R.,Soil And Irrigation Dep Eead Csic Associated Unit | Sellam F.,Institute National Agronomique | Topcu S.,Cukurova University | And 7 more authors.
Agricultural Water Management | Year: 2012

One of the main constraints of irrigated agriculture is off-site N pollution due to export of nitrate in irrigation return flows (IRF). Models capable of simulating the growth of crops and the N loads in IRF as affected by irrigation and N fertilization may be valuable tools in watershed studies. The Agricultural Policy Environmental eXtender (APEX) model was used to assess best management practices for reducing off-site N loads in the IRF of three Mediterranean irrigated watersheds (Akarsu in Turkey, La Violada in Spain and Sidi Rached in Algeria). The watersheds (ranging from 4013 to 10,971ha) were monitored along three hydrological years to determine the volume of IRF and the NO 3-N concentrations and loads in IRF. APEX was calibrated with the data of the first two years and validated with the last year's data. APEX adequately simulated crop evapotranspiration and the volume of IRF and N loads in the IRF (errors<20%). Simulated annual values were in general more accurate than simulated monthly values. APEX predicted that improving irrigation management (change of irrigation system and/or scheduling) will decrease N loads in IRF over current values by 45% (Akarsu), 40% (La Violada), and 8% (Sidi Rached). However, improved N fertilization only will reduce N loads in IRF by 17% (Akarsu) or below 5% (La Violada and Sidi Rached). Improving irrigation management will increase IRF NO 3-N concentrations by 19% in La Violada and will decrease or will remain the same in the other two watersheds. APEX simulations identified the main soils (shallow and low water holding capacity soils) and crops (heavily fertilized or shallow-root crops) N polluters within the studied watersheds. Overall, APEX simulated that the improvement of irrigation performance was the best management strategy to decrease off-site N pollution while maintaining or increasing crop yields in the three studied Mediterranean watersheds. © 2011 Elsevier B.V.

Salmeron M.,Soil And Irrigation Dep Eead Csic Associated Unit | Cavero J.,CSIC - Aula Dei Experimental Station | Quilez D.,Soil And Irrigation Dep Eead Csic Associated Unit | Isla R.,Soil And Irrigation Dep Eead Csic Associated Unit
Agronomy Journal | Year: 2010

Under semiarid Mediterranean conditions irrigated maize (Zea mays L.) has been associated with nitrate pollution of surface water and groundwater. Cover crops grown during the intercrop period of maize could reduce N leaching. A 2-yr experiment was conducted in drainage lysimeters with three cover crops: barley (Hordeum vulgare L), winter rape (Brassica rapa L.), or common vetch (Vicia sativa L.). Bare soil was used as control treatment. Maize was fertilized with 300 kg ha-1 N in the control, and this amount was reduced after a cover crop according to the N content in the aboveground cover crop biomass. Barley and winter rape biomass had a higher N content than vetch (130-170 vs. 50 kg ha-1). The vetch treatment did not reduce N leaching or affect maize yield. The barley and winter rape treatments reduced N leaching by 80% compared to the control (25 kg ha-1 yr-1) mainly due to a reduction of NO3-N concentration in drainage. Maize yield was reduced by 2.7 Mg ha-1 after barley and winter rape but still high (≈14 Mg ha-1). This reduction was due to an N deficiency caused by lower soil N in spring after the cover crop and insufficient N mineralization and/or lack of synchronization with maize N uptake. To use nonlegume winter cover crops to reduce N leaching in monoculture maize it is necessary to consider that N mineralization may not be sufficient to fulfill maize N requirements and N fertilizer adjustment tools should be developed. © 2010 by the American Society of Agronomy.

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