Winter Cover Crops Affect Monoculture Maize Yield and Nitrogen Leaching under Irrigated Mediterranean Conditions

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 NO 3 –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.