Interest in cool-season forage grasses exists because not all soils are suited to growing alfalfa. In the Northeast, it is not uncommon for producers to plant alfalfa with a cool-season grass such as timothy, orchardgrass, or tall fescue in proportions of alfalfa:grass of 2:1 to 3:1 (depending on the grass species), with a total seeding rate of about 20 pounds per acre. The best alfalfa-growing soils are deep, well-drained loams that permit alfalfa taproots to penetrate far into the soil profile. Some soils have fertile topsoil with much less desirable subsoil, including high acidity and/or a fragipan that limits good drainage. Grasses have dense, fibrous root systems that don‘t penetrate nearly as deep into the soil making them more suitable for tough soils (Thomas and Mahanna, 2012).
Alfalfa tap roots store nutrients needed for the next crop and do not regrow from the cut stems but rather from crown buds. Grasses do not have tap roots and regrow from the cut stems. Nutrients for the following crop are stored in the bottom few inches of grasses, so cutting height can impact both regrowth and stand life. The trend toward disc mowers (versus sickle bar mowers) has resulted in lower stubble heights because disc knives are less apt to be damaged from scalping the soil surface or hitting rocks. Reduced grass stand life can be caused by short stubble height due to grass not having enough nutrients in the remaining stubble for normal regrowth. While it may be acceptable to mow alfalfa to a 2-inch stubble height, many agronomists now recommend a 4-inch stubble height for cool-season forage grasses (Thomas and Mahanna, 2011).
Grass species differ in their tolerance to soil drainage and seasonal growing conditions. Reed canarygrass will tolerate very wet soils, while orchardgrass will not. Orchardgrass and tall fescue will produce well under typical summer growing conditions, while timothy grow well in the spring but will become somewhat dormant during the heat of the summer. Orchardgrass is high-yielding but requires aggressive management and is more susceptible to winter damage, particularly ice sheets.
Forage quality also differs among grass species. Cornell University research reported somewhat higher forage quality for tall fescue versus reed canarygrass when both were harvested at the boot stage. If establishing a pure stand of grass, it is best to use one species because there are considerable differences in heading date among cool-season grasses and also between varieties. In recent years, the cool-season grass species generating the most interest is endophyte-free tall fescue. There are dozens of tall fescue varieties on the market, most which head at about the same calendar date as do the latest-maturing orchardgrass varieties (Thomas and Mahanna, 2015). There can also be large differences in maturity within the species. For example, early maturity varieties of timothy and orchardgrass head out at least 10 days earlier than late-maturity varieties of the same species. There is somewhat less varietal difference in the heading dates of reed canarygrass, tall fescue, and bromegrass. Within a species, there is little difference in forage quality when the varieties are harvested at the same stage of maturity. However, there are significant differences in varietal yield within a species, so variety selection is important (Thomas and Mahanna, 2011).
Research at the University of Minnesota found that tall fescue and orchardgrass had higher yield and quality than did alfalfa, and forage analyses predicted that both milk per acre and milk per ton would be higher for the two grasses. However, even though the neutral detergent fiber (NDF) in grass is more highly digestible than alfalfa NDF, the digestion rate is slower which may limit the amount of grass that can be fed to high-producing dairy cows. The farms that have the most success feeding grass put a high priority on harvesting any grass that will be fed to high-producing cows when it‘s still in the boot stage (Thomas and Mahanna, 2015).