Biodiversity effects on yield and unsown species invasion in a temperate forage ecosystem.

Swedish University of Agricultural Sciences, Department of Crop Production Ecology, Box 7043, SE-750 07 Uppsala, Sweden.
Annals of Botany (Impact Factor: 3.45). 02/2009; 103(6):913-21. DOI: 10.1093/aob/mcp008
Source: PubMed

ABSTRACT Current agricultural practices are based on growing monocultures or binary mixtures over large areas, with a resultant impoverishing effect on biodiversity at several trophic levels. The effects of increasing the biodiversity of a sward mixture on dry matter yield and unsown species invasion were studied.
A field experiment involving four grassland species [two grasses--perennial ryegrass (Lolium perenne) and cocksfoot (Dactylis glomerata)--and two legumes--red clover (Trifolium pratense) and white clover (Trifolium repens)], grown in monocultures and mixtures in accordance with a simplex design, was carried out. The legumes were included either as single varieties or as one of two broad genetic-base composites. The experiment was harvested three times a year over three years; dry matter yield and yield of unsown species were determined at each harvest. Yields of individual species and interactions between all species present were estimated through a statistical modelling approach.
Species diversity produced a strong positive yield effect that resulted in transgressive over-yielding in the second and third years. Using broad genetic-base composites of the legumes had a small impact on yield and species interactions. Invasion by unsown species was strongly reduced by species diversity, but species identity was also important. Cocksfoot and white clover (with the exception of one broad genetic-base composite) reduced invasion, while red clover was the most invaded species.
The results show that it is possible to increase, and stabilize, the yield of a grassland crop and reduce invasion by unsown species by increasing its species diversity.

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    ABSTRACT: Establishment of native grassland species can be impaired by weed populations, presenting considerable economic risk for growers of perennial bioenergy crops. We established switchgrass (Panicum virgatum) in southwestern Wisconsin using four weed management strategies, and established a mixture of diverse grassland species to evaluate productivity of diverse mixtures relative to monocultures. Weed management for switchgrass included pre-emergent glyphosate (1.12kgae/ha; GLY), pre-emergent glyphosate (1.12kgae/ha)+post-emergent 2,4-D (1.06kg ae/ha; GLY+2,4-D), pre-emergent glyphosate (0.14kgae/ha) and imazapic (0.07kg ae/ha; S-IMAZ+GLY), and oats planted as a companion crop+pre-emergent glyphosate (1.12kg ae/ha; GLY+OATS). The diverse species mixture was established with pre-emergent glyphosate (0.14kg ae/ha) and imazapic (0.07kg ae/ha; D-IMAZ+GLY). We estimated plant species composition in 2008 and 2009, and biomass yield in autumn of each year. Imazapic decreased grass weed abundance and 2,4-D decreased broadleaf weed abundance in switchgrass in 2008, whereas there were no differences in weed abundances in 2009. Abundance of grass weeds was negatively correlated with biomass yield, and S-IMAZ+GLY produced greater yield in 2009 (7.31±0.75Mgha−1) than GLY and GLY+OATS. Of the four switchgrass establishment treatments we tested, only S-IMAZ+GLY yielded significantly greater biomass than the diverse species mixture. Total costs of establishment were greatest for D-IMAZ+GLY and equivalent among the four switchgrass treatments. These results contribute to current understanding of the agronomic potential and economic risks of native grassland species for bioenergy crops in the first two years of establishment.
    Biomass & Bioenergy - BIOMASS BIOENERG. 01/2011;
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    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 01/2013; · 3.24 Impact Factor
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    ABSTRACT: Background and aims Legumes are important components of grassland mixtures due to their ability to sustain high yields with moderate nitrogen inputs. This study investigates nitrogen relationships in mixtures of Trifolium pratense and grasses into which a deep-rooted forb was included, and particularly whether these realtionships differ when the forb is a legume or a non-legume species. Methods A field experiment in which mixtures of T. pratense, Phleum pratense, Lolium perenne, and Medicago sativa or Cichorium intybus, and monocropped stands of all species was established in 2007 and harvested in 2008 and 2009. The experiment received a total input of 100 kg ha−1 N yearly. Yield and botanical composition were determined in seven harvests. Species were analysed for 15N abundance, and N2 fixation and N transfer were calculated. Soil samples were analysed twice for inorganic N. Results Non-legumes benefitted from the presence of legumes in terms of N concentration, and the yield of mixtures exceeded that of monocropped non-legumes but not monocropped legumes. The mixture containing M. sativa did not yield more DM or N than did the mixture containing C. intybus. A total of 17.08 kg N ha−1 was transferred from T. pratense to the non-legumes in the mixture in which it was the sole legume species. Conclusions It is concluded that there was a synergy effect in species mixtures, but the effect did not differ between the two deep-rooted species.
    Plant and Soil 08/2013; 370:567-581. · 3.24 Impact Factor

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