Effects of expanding functional trait diversity on productivity and stability in cultivar mixtures of perennial ryegrass

Authors: Lowry, Carolyn; BOSWORTH, SIDNEY - University Of Vermont; Goslee, Sarah; KERSBERGEN, RICHARD - University Of Maine; POLLNAC, FREDRIC - University Of New Hampshire; SKINNER, R HOWARD - Retired ARS Employee; WARREN, NICHOLAS - University Of New Hampshire; SMITH, RICHARD - University Of New Hampshire

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2019
Publication Date: 10/1/2019
Citation: Lowry, C.J., Bosworth, S.C., Goslee, S.C., Kersbergen, R.J., Pollnac, F.W., Skinner, R., Warren, N.D., Smith, R.G. 2019. Effects of expanding functional trait diversity on productivity and stability in cultivar mixtures of perennial ryegrass. Agriculture, Ecosystems and Environment. 287:106691. https://doi.org/10.1016/j.agee.2019.106691.
DOI: https://doi.org/10.1016/j.agee.2019.106691

Interpretive Summary: This work shows that cultivar mixtures of perennial ryegrass grown for forage perform as well, but not better, than the best performing cultivar for a given region. However, increasing functional trait diversity within a cultivar mixture of perennial ryegrass was associated with greater productivity. The impact of this work is that we provide evidence to plant breeders and seed companies about the benefits of increasing functional trait diversity within cultivar mixtures, which can potentially lead to designing forage mixtures with greater productivity and stability.

Technical Abstract: Cultivar mixtures can provide a host of beneficial agroecosystem services in annual grain crops; however, it remains unclear whether these same benefits apply to perennial forage cropping systems, or the degree to which the functional trait diversity of the mixture contributes to these effects. We conducted a field experiment across four locations in the Northeast US in which we grew perennial ryegrass cultivar mixtures varying in cultivar number and range of expression of three functional traits (winter hardiness, heading date, and extended growth) and assessed the effects on dry matter yield and inter-annual yield variability. Trait ratings supplied by the seed company were related to observed variation in perennial ryegrass productivity and/or stability at both the individual cultivar and mixture levels. Winter hardiness was associated with greater perennial ryegrass cumulative biomass, and lower interannual stability. In contrast, extended growth was associated with lower cumulative biomass, and both extended growth and later heading date were associated with greater interannual variability. Overall, cultivar richness was negatively associated with perennial ryegrass biomass and stability; however, the best performing mixtures performed as well as the recommended cultivar for the region. When comparing mixtures with equal cultivar richness, functional trait diversity, measured as the additive trait range, was associated with increased biomass production and over-yielding, but not interannual variability. Cultivar mixtures of perennial ryegrass can lead to improved forage production when specific functional traits are optimized within mixtures. Our results support the growing understanding that efforts to ecologically intensify agriculture through enhancement of crop diversity are more likely to succeed when they explicitly consider the functional traits of the crops involved rather than solely numbers of cultivars or species.