The third technical session dealt with the grass species and variety grazing trial results from coordinated plot trials conducted at the University of Massachusetts, University of Vermont, and ARS, University Park. Dr. Sarah Goslee led off this session talking about plant species diversity in pastures and its impact on productivity, nutritive value, resistance to weed invasion, and economics. Dry matter yield per acre tended to increase as plant species diversity went from just 2-species, to 6-species pastures. Yield per acre was particularly better in a dry year on species diverse pastures versus 2 plant species pastures. This was due to better and deeper root distribution in the soil when deeper rooted plant species were in the plant mixture. Milk production per animal was no different on plant species diverse pastures than on a 2-species pasture. However, owing to the diverse species pastures being more productive, more milk was produced per acre on more diverse plant species pastures - 7000 pounds per acre versus 4700 pounds per acre on a 2-plant species pasture. Weed invasion was much less when plant species mixtures approached 7 to 9 species. More research is needed to determine what forage plant species combinations are best over a wide variety of soil and climatic conditions.
Dr. Stephen Herbert was the next speaker. In his presentation, plant species diversity tended to increase pasture productivity until a 5-species mixture was reached over the 4 years of the study, only in 2011 did the 6 and 7-species mixtures continue to add tonnage to forage yield on average. Within mixtures having the same number of species, there was a broad range of yield that would overlap with yields from mixtures having fewer or more species. Therefore, the varieties and species selected to compose a planting blend were of great importance to yield performance. Extend orchardgrass tended to be the best of the orchardgrasses in Massachusetts for yield, but this was not observed in either PA or VT. Perennial ryegrass was susceptible to winter injury. In summary in Massachusetts, based on yield and four-year revenue stream (long term), Blend 13, a 6-species mix performed best. It was composed of Extend orchardgrass, Boost perennial ryegrass, Select and Summit tall fescue, Slezanka timothy, Kentucky bluegrass, and FSG 9601 red clover.
Dr. Sid Bosworth presented the Vermont plot trial results done on a heavy clay soil with a high water table. Five varieties of Festulolium were badly damaged in winter by white mold. It recovered but was weak in late May compared to other grasses growing in adjacent plots. Perennial ryegrass tend to produce well the first year, but yielded much less and inconsistently, varying from 5 percent of total dry matter yield to 35 percent depending on variety the following years. Species diversity tended to improve dry matter production and suppress weeds the first year. However, by the second year as volunteer grasses and broadleaf weeds invaded, the more diverse mixture yielded less than the 2- species mixture even though the planted grass in both mixtures had declined significantly. The invading grasses gave the 2-species seeded mixture (now more diverse, no longer a 2-species sward) the edge in yield over the 3-4 species and 5-6 species seeded mixtures. The diverse species mixtures continued to suppress weedy grasses and broadleaf weeds and therefore were less productive than the 2-species mix when the grassy weeds and broadleaf weeds were included in the total yield of all mixtures. Pastures as they naturalize tend to drift towards higher diversity from simple seeded mixtures.