1 Section for Crop Sciences, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet2 Department of Agriculture & Ecology, Crop Science, Department of Agriculture & Ecology, Faculty of Life Sciences, Københavns Universitet3 Aarhus University4 Ukrudtsøkologi og Beslutningsstøtte5 Agro Tech A/S6 Institut for Agroøkologi - Jordbrugsproduktion og Bæredygtighed7 Department of Agriculture & Ecology, Crop Science, Department of Agriculture & Ecology, Faculty of Life Sciences, Københavns Universitet8 Section for Crop Sciences, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet
Abstract Background and aims We carried out field experiments to investigate if an agricultural grassland mixture comprising shallow- (perennial ryegrass: Lolium perenne L.; white clover: Trifolium repens L.) and deep- (chicory: Cichorium intybus L.; Lucerne: Medicago sativa L.) rooting grassland species has greater herbage yields than a shallow-rooting two-species mixture and pure stands, if deep-rooting grassland species are superior in accessing soil 15N from 1.2 m soil depth compared with shallow-rooting plant species and vice versa, if a mixture of deep- and shallow-rooting plant species has access to greater amounts of soil 15N compared with a shallow-rooting binary mixture, and if leguminous plants affect herbage yield and soil 15N-access. Methods 15N-enriched ammonium-sulphate was placed at three different soil depths (0.4, 0.8 and 1.2 m) to determine the depth dependent soil 15N-access of pure stands, two-species and four-species grassland communities. Results Herbage yield and soil 15N-access of the mixture including deep- and shallow-rooting grassland species were generally greater than the pure stands and the two-species mixture, except for herbage yield in pure stand lucerne. This positive plant diversity effect could not be explained by complementary soil 15N-access of the different plant species from 0.4, 0.8 and 1.2 m soil depths, even though deep-rooting chicory acquired relatively large amounts of deep soil 15N and shallow-rooting perennial ryegrass when grown in a mixture relatively large amounts of shallow soil 15N. Legumes fixed large amounts of N2, added and spared N for non-leguminous plants, which especially stimulated the growth of perennial ryegrass. Conclusions Our study showed that increased plant diversity in agricultural grasslands can have positive effects on the environment (improved N use may lead to reduced N leaching) and agricultural production (increased herbage yield). A complementary effect between legumes and non-leguminous plants and increasing plant diversity had a greater positive impact on herbage yield compared with complementary vertical soil 15N-access.
Plant and Soil, 2013, Vol 371, Issue 1-2, p. 313-325