Can We Manage Alfalfa Stem Fineness With Varieties and Seeding Rate?

Hay producers want alfalfa that is fine stemmed, rather than course stemmed. This is thought to improve palatability (less "sorting" by livestock), intake, forage quality (digestibility) and marketability. Stem fineness is more important when alfalfa is harvested as dry hay rather than haylage. Hay producers are more likely willing to sacrifice some yield potential for an improvement in stem fineness if necessary, whereas haylage producers are not. Anecdotal differences between varieties and seeding rates with regards to stem fineness are often talked about, but without good data to support it. The East-Central Soil & Crop Improvement Association utilized an OSCIA Regional Grant to answer some of these questions.

Variety Differences
A side-by-side variety performance trial was set up at the farm of Eric Bowman, Enniskillen. This was a cooperative project shared with the University of Guelph and the Ontario Forage Crops Committee (OFCC). The trial included 49 commercially available alfalfa varieties side-by-side in 1 X 6 metre plots that were replicated 4 times These plots were harvested and evaluated for yield, maturity and stem diameter in Years 1, 2, and 3 following the establishment year.

Relative maturity of each variety was measured by sorting stems by stage and a "mean stage by weight" was calculated. Stem diameters of Stage 4 (late bud) were measured with electronic calipers to determine "stem fineness" when cutting at that stage. Maturity and stem diameter data was pooled with a similar trial at Elora. Varieties significantly different (p=0.05) for maturity and stem diameter are listed in Tables 1 and 2.

Table 1 - Alfalfa Varieties With Maturity Significantly Different Than The Trial Mean

Table 2 - Alfalfa Varieties With Late-Bud Stage Stem Diameter Significantly Less Than The Trial Mean

Harvest timing and variety selection are both management options for producing finer stemmed hay. Harvesting any alfalfa variety at an earlier stage of development will result in forage that has a greater proportion of finer stemmed, less mature material. However, varieties also differ in their stem diameter as well as their maturity, so some varieties are finer stemmed at the same stage of maturity. Since there was not a high correlation with yield, this does not necessarily have to be sacrificed. Seeding early-maturing as well as late-maturing varieties can be an option to widen the first-cut harvest window.

Variety yield data was added to the composite index data published in the 2009 OFCC Forage Variety brochure (www.goforages.ca).

Seeding Rate
A seeding rate trial, similar to the variety trial, was seeded in 2006 under good conditions, and harvested in 2007 and 2008 to determine if an increased seeding rate increases stem fineness. Five varieties were planted at seeding rates of 5.5, 11, 16.6 and 22 kg/ha.

Table 3 - Effect of Alfalfa Seeding Rate On Maturity, Stem Diameter and Yield

The alfalfa plots seeded at higher rates were less mature than the lower seeding rates. However, there were no differences in stem diameter at the same stage of maturity (late-bud). In other words, high seeding rates delayed maturity, and therefore reduced stem diameter on a given date of harvest, but not at the same stage.

Full Report
A full project report will be posted when available on the East-Central SCIA website:
www.regionalscia.org/.