The first thing to consider in selecting an alfalfa variety is yield, but it’s not the only thing, says University of California (UC), Davis, Extension Agronomist Dan Putnam.

During a recent alfalfa and forage field day at the Kearney Agricultural Center at Parlier, Putnam outlined other points to ponder in choosing a new variety.

He showed visitors a test plot of about 30 released and 22 experimental alfalfa varieties, with CUF 101 as the standard, planted in 2002 for comparison. It is part of a statewide program including plots at Tulelake, Davis, Five Points, and the Imperial Valley. He also distributed tabulated results of yields of recent seasons.

“Keep in mind that when you walk into a production field, you can’t know whether the variety is the right one. But when you look at varieties planted side-by-side you begin to see some differences between varieties,” he said.

“Yield is probably the most important trait of an alfalfa variety,” the alfalfa specialist continued, “since it integrates many other traits, including fall dormancy and pest resistance.”

His second consideration is biotech traits, and the program has tested Roundup Ready alfalfa varieties for about four years. These varieties withstand glyphosate herbicide applied to them for weed control.

“Basically, remember with these you are buying a technology and not just the variety,” Putnam commented.

Roundup Ready alfalfa, however, is currently suspended under a federal district court ruling pending completion of an environmental impact statement on biotech alfalfa.

Putnam said a conservative estimate on the difference the best-suited variety can make would be in the range of $600 to $700 per acre, given the current alfalfa market. This is possible by paying as little as $2 per pound more for a 20-pound per acre seeding rate, or $40 per acre.

“So, yes, it is worth your while to be cautious about variety choice. Granted, a variety may not perform for you like it did in our trials, and that’s why the key question is performance and not the price of the seed,” Putnam said.

And, he recommended, look at multi-year data, not just a single year. Although a seed company may tout a variety after one year’s performance, the important thing is what it does the second and third seasons.

Putnam said it’s helpful to consider the top third of the performers among certified entries in the UC trials. “It may be hard to figure out where the cut-off is, but at least it will give you an indication of how these varieties perform under controlled conditions. Generally, they will match what growers experience in the field.”

Growers who still have their doubts can set up their own strip trials, often with the cooperation of seed companies, to gauge varieties under real conditions and practices in their fields.

Turning to fall dormancy, Putnam pointed to a single strip of a fall dormant variety that was noticeably shorter than the rest. Fall dormancy, he explained, is a measurement (typically ranging from 3 to 10) of regrowth during October when the most dramatic differences are seen.

In the 2005-2006 trial at KAC, average yield peaked at about 12.5 tons with varieties having a fall dormancy rating of about 9 and then declined. “Generally, if you are below a 7 in the area around Parlier, you will take some fall hits in fields,” he said.

However, among 8 and 9 ratings, yields were not consistent, so he recommended growers concentrate on yield to consider fall dormancy first, then select for yield.

Growers seeking quality, he noted, should be prepared for the trade-off with yield. In trials at UC, Davis during 2002-2004, as fall dormancy declined from 8 to 4, yield was about 2 tons per acre less.

“But at the same time, quality increases with lower dormancy at the same cutting schedule,” he said, adding that in this season of high hay prices, non-dairyman growers will likely go for higher yield.

Pest resistance in a variety can be considered “a strategic management factor,” and resistance to Phytophthora and other root diseases, along with aphids in the southern San Joaquin Valley, should be high.

Some growers, he said, overlook “disease and insect resistance packages” offered by certain varieties. “If something like stem nematode breaks out two or three years later, there’s not much you can do. When you have a problem, you can’t do much more than contain it in a field, but you could have prevented it by planting a resistant variety.

“Talk with your farm advisor and PCA to see that you have a variety with a level of resistance adequate for your particular ranch.”

What about persistence in a variety? That depends on how long the grower wants to have the field in production. “Some may want it as long as possible,” Putnam said, “but others may be on a rotation schedule. Generally, most fields in this area last three to four years, and in the San Joaquin Valley our trials with high fall dormancy varieties, particularly with a 25-day cutting schedule, tend to be less persistent.”

Finally, Putnam reminded growers that price (including hats or other premiums) should be their last consideration in choosing a variety. “When everything else is good, then look at price, but don’t make it your main criterion.”

Putnam said trials at UC Davis also investigated the comparative effects of wheel traffic and cutting schedules on performance of 20 alfalfa varieties.

There are two effects of wheel traffic: the soil compaction itself and the crushing of the new stems. “We think the effect on the new stems is pretty important,” he said.

“We found the overall effect of wheel traffic on yield is pretty dramatic: 25 percent to 30 percent. In the plots we just ran over every square inch of the field twice with a tractor, not the regular ‘alfalfa abuse’ of swathers, one-ton balers, fertilizer trucks, and the rest of it.”

The study did reveal differences by variety to the traffic. “The key question — and one that breeders often ask — is whether you want a variety that comes back quickly or not after cutting.”

Higher fall dormancy varieties tend to grow back sooner, and, Putnam explained, “that four to six days earlier is exactly when the wheel traffic is being applied and the tiny stems are crushed.”