Interseeding cover crops into maize: Characterization of species performance under Mediterranean conditions

Cover crop (CC) benefits and adoption in crop rotations may be limited by the short planting window after the cash crop. Interseeding or relay intercropping of CC is a technique that could overcome short planting windows constraints and allow CC establishment and growth. However, in Mediterranean regions this technique has been poorly implemented. Field experiments were established in Central Spain during two consecutive growing seasons to assess the performance of different species as interseeded crops into irrigated maize (Zea mays L.). The treatments included annual ryegrass (Lolium multiflontm L.) and eight legumes: burr medic (Medicago polymotpha L.), barrel medic (Medicago truncatula L.), yellow sweetclover (Melilotus officinalis L.), berseem clover (Trifolium alexandrinum L.), balansa clover (Trifolium michelanium L.), red clover (Trifolium pratense L.), Persian clover (Trifolium resupinatum L.), and common vetch (Vicia sativa L.). A bare soil was included as control treatment. After the maize harvest, the four species with the best performance were planted as autumn cover crops in adjacent plots. The ground cover was studied throughout the experimental period, and biomass and N content for each species were determined in the autumn and in the following spring prior to the cover crop termination. The soil inorganic N content was determined in spring. Barrel medic, yellow sweetclover, common vetch and annual ryegrass were the species with the best performance in terms of soil coverage during the summer. Red clover and Persian clover had good establishment in one out of two years. None of the interseeded species impaired maize grain yield or quality. Interseeded species achieved better soil coverage and increased the biomass accrued at autumn compared to cover crops sown in October. Therefore, interseeded species ensured longer ground coverage, increasing the potential for soil quality improvement or weed suppression. Moreover, the higher biomass achieved by interseeded species ensured the survival of yellow sweetclover, which was winter killed when planted in the autumn. Interseeded cover crops enhanced the potential of N leaching reduction compared to autumn cover crops. This experiment confirms the suitability of different species interseeded in summer into irrigated maize in Mediterranean regions, and highlights the extra benefits of this practice in annual rotations.