Summary 1.A coordinated continental-scale field experiment across 31 sites was used to compare the biomass yield of monocultures and four species mixtures associated with intensively managed agricultural grassland systems. To increase complementarity in resource use, each of the four species in the experimental design represented a distinct functional type derived from two levels of each of two functional traits, nitrogen acquisition (N 2 -fixing legume or nonfixing grass) crossed with temporal development (fast-establishing or temporally persistent). Relative abundances of the four functional types in mixtures were systematically varied at sowing to vary the evenness of the same four species in mixture communities at each site and sown at two levels of seed density. 2. Across multiple years, the total yield (including weed biomass) of the mixtures exceeded that of the average monoculture in >97% of comparisons. It also exceeded that of the best monoculture (transgressive overyielding) in about 60% of sites, with a mean yield ratio of mixture to best-performing monoculture of 1Á07 across all sites. Analyses based on yield of sown species only (excluding weed biomass) demonstrated considerably greater transgressive overyielding (significant at about 70% of sites, ratio of mixture to best-performing monoculture = 1Á18).3. Mixtures maintained a resistance to weed invasion over at least 3 years. In mixtures, median values indicate <4% of weed biomass in total yield, whereas the median percentage of weeds in monocultures increased from 15% in year 1 to 32% in year 3. 4. Within each year, there was a highly significant relationship (P < 0Á0001) between sward evenness and the diversity effect (excess of mixture performance over that predicted from the monoculture performances of component species). At lower evenness values, increases in community evenness resulted in an increased diversity effect, but the diversity effect was not significantly different from the maximum diversity effect across a wide range of higher evenness values. The latter indicates the robustness of the diversity effect to changes in species' relative abundances. 5. Across sites with three complete years of data (24 of the 31 sites), the effect of interactions between the fast-establishing and temporal persistent trait levels of temporal development was highly significant and comparable in magnitude to effects of interactions between N 2 -fixing and nonfixing trait levels of nitrogen acquisition. 6. Synthesis and applications. The design of grassland mixtures is relevant to farm-level strategies to achieve sustainable intensification. Experimental evidence indicated significant yield benefits of four species agronomic mixtures which yielded more than the highest-yielding monoculture at most sites. The results are relevant for agricultural practice and show how grassland mixtures can be designed to improve resource complementarity, increase yields and reduce weed invasion. The yield benefits were robust to considerable changes in the relative propo...

Grassland diversity can support sustainable intensification of grassland production through increased yields, reduced inputs and limited weed invasion. We report the effects of diversity on weed suppression from 3 years of a 31‐site continental‐scale field experiment.At each site, 15 grassland communities comprising four monocultures and 11 four‐species mixtures based on a wide range of species' proportions were sown at two densities and managed by cutting. Forage species were selected according to two crossed functional traits, “method of nitrogen acquisition” and “pattern of temporal development”.Across sites, years and sown densities, annual weed biomass in mixtures and monocultures was 0.5 and 2.0 t  DM ha−1 (7% and 33% of total biomass respectively). Over 95% of mixtures had weed biomass lower than the average of monocultures, and in two‐thirds of cases, lower than in the most suppressive monoculture (transgressive suppression). Suppression was significantly transgressive for 58% of site‐years. Transgressive suppression by mixtures was maintained across years, independent of site productivity.Based on models, average weed biomass in mixture over the whole experiment was 52% less (95% confidence interval: 30%–75%) than in the most suppressive monoculture. Transgressive suppression of weed biomass was significant at each year across all mixtures and for each mixture.Weed biomass was consistently low across all mixtures and years and was in some cases significantly but not largely different from that in the equiproportional mixture. The average variability (standard deviation) of annual weed biomass within a site was much lower for mixtures (0.42) than for monocultures (1.77). Synthesis and applications. Weed invasion can be diminished through a combination of forage species selected for complementarity and persistence traits in systems designed to reduce reliance on fertiliser nitrogen. In this study, effects of diversity on weed suppression were consistently strong across mixtures varying widely in species' proportions and over time. The level of weed biomass did not vary greatly across mixtures varying widely in proportions of sown species. These diversity benefits in intensively managed grasslands are relevant for the sustainable intensification of agriculture and, importantly, are achievable through practical farm‐scale actions.

Kirwan, L., Connolly, J., Brophy, C., Baadshaug, O. H., B?langer, G., Black, A., Carnus, T., Collins, R. P., ?op, J., Delgado, I., De Vliegher, A., Elgersma, A., Frankow-Lindberg, B. E., Golinski, P., Grieu, P., Gustavsson, A., Helgad?ttir, ?., H?glind, M., Huguenin-elie, O., J?rgensen, M., Kadziuliene, Z., Lunnan, T., L?scher, A., Kurki, P., Porqueddu, C., Sebastia, M. T., Thumm, U., Walmsley, D. & Finn, J. A. (2014). The Agrodiversity Experiment: three years of data from a multisite study in intensively managed grasslands. Ecology, 95 (9), [2680]Intensively managed grasslands are globally prominent ecosystems. Weinvestigated whether experimental increases in plant diversity in intensively managedgrassland communities can increase their resource use efficiency.This work consisted of a coordinated, continental-scale 33-site experiment. The core designwas 30 plots, representing 15 grassland communities at two seeding densities. The 15communities comprised four monocultures (two grasses and two legumes) and 11 four-speciesmixtures that varied in the relative abundance of the four species at sowing. There were 1028plots in the core experiment, with another 572 plots sown for additional treatments. Sitesfollowed a protocol and employed the same experimental methods with certain plotmanagement factors, such as seeding rates and number of cuts, determined by local practice.The four species used at a site depended on geographical location, but the species were chosenaccording to four functional traits: a fast-establishing grass, a slow-establishing persistentgrass, a fast-establishing legume, and a slow-establishing persistent legume. As the objectivewas to maximize yield for intensive grassland production, the species chosen were all highyieldingagronomic species.The data set contains species-specific biomass measurements (yield per species and of weeds)for all harvests for up to four years at 33 sites. Samples of harvested vegetation were alsoanalyzed for forage quality at 26 sites.These data should be of interest to ecologists studying relationships between diversity andecosystem function and to agronomists interested in sustainable intensification. The largespatial scale of the sites provides opportunity for analyses across spatial (and temporal) scales.The database can also complement existing databases and meta-analyses on biodiversity?ecosystem function relationships in natural communities by focusing on those samerelationships within intensively managed agricultural grasslands.publishersversionPeer reviewe

Summary Increased species diversity promotes ecosystem function; however, the dynamics of multi‐species grassland systems over time and their role in sustaining higher yields generated by increased diversity are still poorly understood. We investigated the development of species’ relative abundances in grassland mixtures over 3 years to identify drivers of diversity change and their links to yield diversity effects. A continental‐scale field experiment was conducted at 31 sites using 11 different four‐species mixtures each sown at two seed abundances. The four species consisted of two grasses and two legumes, of which one was fast establishing and the other temporally persistent. We modelled the dynamics of the four‐species mixtures, and tested associations with diversity effects on yield. We found that species’ dynamics were primarily driven by differences in the relative growth rates (RGRs) of competing species, and secondarily by density dependence and climate. The temporally persistent grass species typically had the highest RGRs and hence became dominant over time. Density dependence sometimes induced stabilising processes on the dominant species and inhibited shifts to monoculture. Legumes persisted at most sites at low or medium abundances and persistence was improved at sites with higher annual minimum temperature. Significant diversity effects were present at the majority of sites in all years and the strength of diversity effects was improved with higher legume abundance in the previous year. Observed diversity effects, when legumes had declined, may be due to (i) important effects of legumes even at low abundance, (ii) interaction between the two grass species or (iii) a store of N because of previous presence of legumes. Synthesis. Alongside major compositional changes driven by RGR differences, diversity effects were observed at most sites, albeit at reduced strength as legumes declined. This evidence strongly supports the sowing of multi‐species mixtures that include legumes over the long‐standing practice of sowing grass monocultures. Careful and strategic selection of the identity of the species used in mixtures is suggested to facilitate the maintenance of species diversity and especially persistence of legumes over time, and to preserve the strength of yield increases associated with diversity.

The changes in dry matter (DM) yield, botanical composition and nutritive value of herbage to ruminants of two wet grasslands, Arrhenatherum elatius grassland (Experiment 1) and a Molinia caerulea fen meadow (Experiment 2), in which a range of cutting and fertilizer treatments were imposed in 1999, were assessed after 4-7 years of treatment imposition. Both experiments had a split-plot design with four replicates. In Experiment 1 the three main-plot cutting treatments were two cuts with a delayed first cut, three cuts and four cuts during the growing season of each year. In Experiment 2 the cutting treatments were two cuts with a traditional harvest time, two cuts with a delayed first cut and three cuts. The four sub-plot fertilizer treatments were an unfertilized control, application of a phosphorus and potassium (PK) fertilizer, application of a nitrogen (N) and PK fertilizer to the first cut only (N 1 PK) and application of PK plus N applied to each of two, three or four cuts (N C C PK). Application of fertilizer influenced yield and botanical composition of herbage more than the cutting treatments while the opposite occurred for nutritive value of the herbage. Application of fertilizer increased the proportion of tall grasses in Experiment 1 and forbs in Experiment 2. The proportion of Equisetum palustre, present only in Experiment 1, was reduced from 0AE33 to less than 0AE01 by increased cutting frequency together with the NPK fertilizer treatments. In Experiment 1 diversity of vascular plants was negatively affected only by the four-cuts treatment while on both wet grasslands other cutting and fertilizer application treatments had no effect. Changes in DM yield of herbage caused by the cutting and fertilizer application treatments were similar for both vegetation types with DM yield increased significantly by fertilizer application but only slightly or not reduced by increasing the cutting frequency. Nutritive value of herbage was positively correlated with cutting frequency and was most influenced at the first cut.