Carefully select alfalfa varieties

By DAN UNDERSANDER

Many of us carefully select corn hybrids and soybean varieties, but choose alfalfa varieties based on price, marketer, etc., rather than performance. Yet, the differences among alfalfa varieties are at least as great as those of corn and soybeans.

It costs about as much to grow a low-yielding variety as a high-yielding variety. Land cost, taxes, machinery cost, fertilizer, and herbicide costs are all about the same.

Harvesting costs also are about the same, regardless of yield. It takes only about 15% more energy to harvest 2 tons per acre than 1 ton per acre, and labor is about the same.

Trouble is, yields vary widely. Top-yielding varieties in University of Wisconsin trials average about 40% more — 1.3 tons per acre in the first year — than the lowest-yielding varieties.

With hay at $100 per ton, this alone would more than pay for the total seed cost of the most expensive variety!

And the yield spread widens in subsequent years. Each year thereafter, the top-yielding variety averaged more than 2.3 tons per acre more than the bottom-yielder — even in drought years.

Selecting the best variety, regardless of the seed cost, will pay for itself every year of the stand.

That’s why I recommend premium varieties, even for green manure or other very short rotations.

Winter survival comes next

We all want alfalfa to survive winter, and recognize that enough winter-hardiness is needed. However, the greatest loss to most alfalfa growers isn’t stand kill, but stand injury.

Alfalfa starts shoots in the fall for spring growth. If these shoots are killed over winter, then the plant must start over making new shoots in the spring. Consequently, first-cutting yield is reduced due to the later start.

According to my trials, a lower winter survival score (more winter-hardiness) is needed near Madison, Wis., where the snow comes and goes over winter than further north, where snow cover remains most winters.

A cold spell during a period of no snow cover can really injure alfalfa.

The highest yields in my trials over the past 20 years have been with varieties having a winter survival score of 2 or less.

The reason? The shoots from the more winter-hardy plants didn’t have to start over.

Select for insect, disease resistance

Most varieties have very high resistance to anthracnose, bacterial wilt, fusarium, phytophthora, and verticillium (disease resistance score near 30).

But in the Midwest, we also need aphanomyces resistance. Race 2 resistance is recommended because it includes resistance to Race 1 and some others.

Potato leafhopper resistance isn’t used as often as it would be beneficial.

In some areas, this trait can eliminate the need to spray or reduce sprayings.

Consider fall dormancy 5

Varieties grown in the Midwest with fall dormancy 4 ratings tend to yield more than fall dormancy 3. Now, some companies are releasing alfalfa varieties with fall dormancy 5.

Generally, the higher the fall dormancy, the quicker the varieties start growing in spring and after each cutting. This can result in higher yields and more late-fall yield.

The challenge with a fall dormancy 5 variety is, since shoots come back faster, the hay/haylage must get off the field more quickly to avoid driving over the new shoots and reducing the next cutting yield. I’d recommend it especially for haylage fields.

For more information on alfalfa variety traits check my website at www.uwex.
edu/ces/forage.

Undersander is a University of Wisconsin Extension forage agronomist.

Scrutinize alfalfa seed quality

Seed certification tags are verification of purity, weed seeds, germination scores and more. But there are some things to check carefully. For instance, any germ test that’s a year or more old should be suspect.

High-quality forage seed should have a germination score above 90% and a purity above 98%, for a minimum pure live seed of 88%, unless seed is coated (which maybe 8% to 35% of the seed weight). Germination is the percent of seeds that germinate in a standard test, plus hard seed (seeds that don’t take up moisture).

Both can be expected to germinate within 30 to 60 days of planting. The same is true for cool-season grasses such as bluegrass, orchardgrass and tall fescue.

Seed purity should be high. Purity is 100 minus the percentages of weed seed, other crop seed (which should be less than 1%), and inert materials such as dirt, chaff and seed coating.

Pure live seed, or PLS, in the bag is what you really want to calculate, and compare prices based on it. PLS is the percent germination times percent purity divided by 100. If you divide the pounds of PLS in a bag by the price per bag, you get a price per pound of actual live seed.

The accompanying table calculates that actual cost at varying prices and PLS. Note that a bag of seed costing $225 with 65% PLS is more expensive per 50 pounds of live seed than a bag costing $275 with 85% PLS.

— Dan Undersander

This article published in the February, 2011 edition of AMERICAN AGRICULTURIST.

All rights reserved. Copyright Farm Progress Cos. 2011.