Effects of undersown crops on soil mineral N and grain yield of spring barley

Undersowing a cereal crop can reduce nitrogen (N) leaching and increase available N for the successive crop. An undersown crop can also compete with the main crop. Seventeen plant species were undersown in spring barley (Hordeum vulgare L.) to study their suitability regarding establishment, biomass production, competition with the main crop and effects on soil mineral N. Three different seeding rates were evaluated. Italian ryegrass (Lolium multiflorum Lam.) decreased nitrate nitrogen (NO3-N) content in late autumn and timothy (Phleum pratense L.) in the succeeding spring. A mixture was optimal to reduce N leaching. Italian ryegrass is a very competitive species that should be undersown at moderate seeding rates to avoid large yield reduction in the main crop. Black medic (Medicago lupulina L.) slightly increased N leaching risk, but red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) did not increase soil NO3-N content. As clovers did not compete strongly with the main crop, fairly high seeding rates can be used to maximise N fixation to benefit the successive crop.