Performance of Forage Mixtures Constructed to Fulfill Multiple Functional Roles.

Ecological theory predicts that complex pasture communities that include numerous plant functional types should be more productive, stable, and better at excluding weeds than simple communities with few functional types. In a series of greenhouse and field studies, six unique functional attributes contributing to forage productivity were identified and 23 temperate pasture species were screened for their ability to perform each function. These functions included, 1) early-spring growth, 2) late-spring growth, 3) summer growth and drought resistance,  4) fall growth, 5) lack of sensitivity to low fertilizer N inputs (mainly through N fixation), and 6) ability to spread and colonize bare soil. In a follow-up field study, 14 of the species were sown as monocultures or combined into six 2-species mixtures, five 3-species mixtures, six 4-species mixtures, and five 6-species mixtures. Nested within each level of species complexity were varying levels of functional complexity including mixtures that maximized the number of positive functional attributes and mixtures that were designed to include species that performed poorly in fulfilling the identified functions. Plots were planted in the fall of 2004, then grazed by beef cattle four or five times per year in 2005, 2006, and 2007. This presentation will focus on annual yield and weed exclusion data and will discuss results in light of the following hypotheses: 1) inclusion of more functional attributes (rather than more species) and redundancy in these functional attributes among species increases seasonal evenness as well as total plant production; 2) functional attributes of species and redundancies among species are additive and the negative tradeoffs of these attributes are subtractive; 3) the increase in plant productivity over a greater portion of the season minimizes invasion success of non-desirable species.