Biodiversity effects on yield and unsown species invasion in a temperate forage ecosystem.
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.
Full-textDOI: · Available from: B. E. Frankow-Lindberg, May 09, 2015
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ABSTRACT: Formulating grass-legume mixtures requires knowledge of how the proportion of species in a seed mixture (i.e., species evenness) affects productivity and weed abundance. We hypothesized that mixtures with more equal proportions of species in the seed mixture (i.e., greater species evenness) would have greater productivity and fewer weeds than mixtures dominated by one or two species or monocultures. Two experiments with 15 mixtures and monocultures of orchardgrass (Dactylis glomerata L.), quackgrass (Elytrigia repens L.), alfalfa (Medicago sativa L.), and white clover (Trifolium repens L.) (Exp. 1) or 15 mixtures and monocultures of meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], reed canarygrass (Phalaris arundinacea L.), red clover (T. pratense L.), and kura clover (T. ambiguum L.) (Exp. 2) were sown in autumn 2008 at four locations in Pennsylvania and Wisconsin. In each experiment, there were four monocultures, four mixtures dominated by one species, six mixtures dominated by pairs of species, and one equal mixture. Mixtures and monocultures were harvested four to five times each year from 2009 to 2011. Mixtures often had more biomass than the average of legume or N-fertilized grass monocultures. Mixtures with more equal proportions of species in the seed mixture, however, did not have more biomass or fewer weeds than other mixtures. Rather, differences in yield were related to the dominant species in the mixture. Optimal legume percentages (30-40%) in the harvested biomass were achieved with a wide range of grass and legume seed proportions, which suggested that farmers have wide flexibility in formulating seed mixtures for pastures.Agronomy journal 09/2013; 105(5):1289. DOI:10.2134/agronj2013.0131 · 1.54 Impact Factor
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ABSTRACT: Increasing plant species diversity in grasslands may improve productivity and stability of yields. In a field experiment, we investigated the herbage dry-matter (DM) yield and crude protein content of two-species swards of perennial ryegrass–white clover (Lolium perenne L.–Trifolium repens L.) and three-species swards of ryegrass–white clover with red clover (Trifolium pratense L.). Five different managements represented cutting, grazing and combinations thereof, with different slurry fertilization treatments in 1- to 4-year-old swards. The three-species mixture out-yielded the two-species mixture in years 1 and 2. Across all 4 years, yields were 8–10% higher in cut swards. Inclusion of red clover increased the yields of clover across the 4 years by 51% without fertilizer and by 90% when fertilized. Responses to slurry fertilization were similar in both mixtures and were mainly independent of sward age. There was a complementary effect over the season and across managements. Red clover dominated in the first and third cuts; white clover dominated in the second and fourth cuts. Red clover dominated in cut swards and white clover in grazed swards. Future prospects of the inclusion of red clover in sown swards are discussed. These may include higher nitrogen-use efficiency in ruminants, increased soil fertility and improved sward flexibility to cope with changing managements. The findings also suggest positive yield effects of alternating between cutting and grazing within the season or between years.Grass and Forage Science 06/2014; 69(2). DOI:10.1111/gfs.12025 · 1.93 Impact Factor
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ABSTRACT: Download publisher version for free - http://authors.elsevier.com/a/1QN7p3IW-wLM-c (until March 5th) Sown biodiverse permanent pastures rich in legumes (SBPPRL) were developed in Portugal in the 1960s and 1970s as a strategy to increase grassland productivity by sowing mixtures of up to 20 species/cultivars of legumes and grasses. Compared to semi-natural pastures, the resulting engineered system provides higher yields of better quality pasture, significantly increasing sustainable stocking rates, with multiple environmental co-benefits. Here, we propose a conceptual framework for the sustainability assessment of SBPPRL and apply it with existing data. Our objective is to inquire if this system is an example of sustainable intensification of livestock production, i.e., an economic and ecological win–win solution that can answer many of the causes for ecosystem degradation in semi-arid and sub-humid climate zones, such as in the Mediterranean basin. We build on experimental results from previous studies, which suggest that SBPPRL replenish soil organic matter pools and improve soil structure. The high increase in stable soil organic matter acts as a carbon sink, turning the system into an optimum tool for climate change mitigation and adaptation. Portugal made use of this fact by supporting the expansion of SBPPRL areas and abating the corresponding carbon from Kyoto Protocol emissions calculations. We resorted to the literature to evaluate other environmental effects due to the absence of data specifically for SBPPRL. Surface water runoff decreases and pirophyte shrub vegetation is eliminated or much reduced. Nitrogen accumulates in stable forms in the soil after being fixed by Rhizobium/legume symbiotic associations. Legumes depend on phosphorus fertilization; as such the nitrogen cycle in SBPPRL relies on a potentially non-renewable resource (required during the first years after installation of the pasture), which may be a potential limiting factor in the future. The effects on wild biodiversity are unclear. The methodology laid out in this article provides an innovative framework to assess these effects as additional experimental data becomes available.Ecological Engineering 01/2015; 77:85-97. DOI:10.1016/j.ecoleng.2015.01.002 · 3.04 Impact Factor