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ABCs of harvesting alfalfa discussed during webinar

April 4, 2013 | 0 comments

Proper harvest management of alfalfa sets the stage for the top quality forages required by today's rising herd averages and high forage rations.

Dr. Ev Thomas packed a haymow full of management details into "ABC's of Harvesting Alfalfa", the latest Hoard's Dairyman/University of Illinois webinar. The veteran agronomist with William H. Miner Agricultural Research Institute pointed out that alfalfa plants don't simply die. They are killed.

In the webinar sponsored by W-L Alfalfas, Thomas told his audience of more than 80 people from across the nation that while declines in alfalfa stands can be traced to insect damage, weed encroachment, foliar diseases, low fertility and frost heaving, the most common culprit is crown damage caused by running the plants over.

Although alfalfa plants can be killed by cutting too frequently or cutting at the wrong time of year, crown damage caused by field traffic as farmers mow, bale and chop, haul and fertilize is the top cause of alfalfa death, Thomas said, and it is the only unavoidable cause.

"Every year, we theoretically run over every alfalfa plant in the field, which can damage the crown and expose it to disease. We killed it and there is nothing we can really do to prevent that," he pointed out.

Since necessary field traffic is the primary cause and disease is the secondary cause of stand decline, Thomas said it makes little sense to manage alfalfa with long stand life as the primary goal, particularly on dairy farms where forage quality is so important.



Mowing Height

Unlike grass, alfalfa stores nutrients for the next crop in its tap root. There is no regrowth from the stubble, which dies soon after mowing. Therefore, Thomas said, alfalfa mowing height has no direct impact on the regrowth rate.

In northern locations, he advises leaving 4-6 inches of stubble for winter to catch and hold snow.

"Leaving high alfalfa stubble really works," he said, explaining the stubble poking through ice sheets in low areas may also reduce winterkill by reducing smothering. "This is based on fact and not just opinion," he said.

Mowing often becomes a bottleneck in hay crop silage production, but producers found that disk mowers can be operated at much higher ground speeds than sickle bar mowers. "There has been a rapid switch to disk bines, which in some cases can be operated at darn near road speeds," Thomas noted.

Disk bines also proved more "bullet-proof" than sickle bar mowers, he added, with fewer broken knives and less downtime.

Farmers quickly responded by mowing closer to the soil surface. "In some cases, mowing became dual-purpose operation - mowing and land leveling," Thomas observed.

Over the past few years, the use of disk mowers has been linked to problematic rising levels of ash.

There are two reasons for more ash potential. Growers are reducing mowing height to as low as one inch, with research finding 500 pounds yield difference per year for every one-inch change in stubble height.

Lowering the cutting height does not have as much impact on forage quality as it might seem, Thomas added, citing a two-year study at Miner on switching from four-inch to two-inch cutting heights. "It looks to me that the increase in yield outweighs the modest decrease in quality on most farms," he remarked.

Disk Mowers and Ash Problems

The second reason, confirmed by tens of thousands of samples, is that disk mowers cause turbulence.

Forage analysis of mineral content and legumes silages showed an increase in mineral content over those years when sickle bar mowers were predominant. The numbers have modified a bit since 2007 as producers respond to the problem, Thomas noted.

Although the average ash content of alfalfa silage is 11 percent, 8 percent of that is ash and mineral content and 3 percent is dirt, meaning soil, manure solids and vegetative debris.

That's fine, Thomas said, but some alfalfa silage has 18 percent ash or about 10 percent dirt, which means that a farmer feeding 10 pounds of alfalfa silage dry matter is actually offering his cows nine pounds of alfalfa and one pound of contaminants.

Not everyone has an ash problem. "Don't make changes unless ash content is high enough to be a potential problem," Thomas advised. "If it's up into the mid-teens, I would certainly check into it", Thomas advised.

It could be machinery scalping the ground or overaggressive raking. Miner research documented that dropping from four inches to two inches did not spark an increase in ash, but dropping from two inches to one inch did. "I think it is a function of knives and what soil moisture conditions are," Thomas noted.

One simple step is to switch from curved to flat disk mower knives. Thomas considers flat knives better because they have less "vacuuming" action. "This is a rather simple, inexpensive either fix or improvement," he said.



Windrow Management

Getting in narrow windrow down to 35-40 percent dry matter means waiting until the top layer is almost too dry, while the bottom layer remains too wet. It's like a farmer having one foot in a bucket of ice and the other foot in a bucket of scalding water. "On average, he's comfortable, but of course he's not," Thomas said.

It's the same with narrow windrow alfalfa. It's too dry on top and too wet on the bottom, which means a lot of leaf shatter and nutrient loss.

Research results in New York State compared wide swath windrows of 75-85 percent of the cutter bar with narrow windrows spanning three feet.

The wide swath alfalfa was ready to chop in seven hours, while the narrow windrows took 25 hours to get to the same dry matter.

For first cut alfalfa silage, taken at 48-inches high, wide windrows provided 20 percent more milk per ton, while second cut grass in wide windrows gave 11 percent more milk per ton.

Don't let alfalfa be the low stave in the dairy's barrel, Thomas said, meaning the practice or condition that most limits profits and production.

Fifty years ago when dairy cows were producing 50 pounds of milk a day, alfalfa with 16 percent protein and 50 percent NDF may have been acceptable, he explained, but it's a low stave in the barrel for modern cows producing 100 pounds of milk a day.



Balancing Risks and Rewards

Intensifying alfalfa harvest management is not without risks, Thomas said, invoking the image of a turtle who doesn't make progress unless he sticks his head out. Dairy farmers must balance risk and rewards in their hayfields through tradeoffs that involve yield, quality and stand life.

Harvesting alfalfa in the mid-bloom to full-bloom stage compared to the full-bud stage often results in higher forage yield, less weed competition and less plant damage.

Thomas cited California research showing alfalfa mowed at 50-100 percent bloom for five cuts a year had no weeds after three years, while alfalfa mowed at bud stage for eight or nine cuts a year had 50 percent weed cover after three years.

There was stand decline because bud stage harvest doesn't permit the full replenishment of root carbohydrates, Thomas noted, and results in plant stress.

Mid-bud yields were 7.9 tons of dry matter per acre, while 50-100 percent bloom yields were 10.3 tons of dry matter per acre.

More harvest means less yield, Thomas said, with one ton per cutting versus two tons per cutting. "Intensifying harvest management has an impact. It really affects yield, weed pressure and, also, plant damage since it was run over eight times rather than five times," he said.



Key Questions

There are two key questions for dairy farmers. Is the primary goal of alfalfa production maximum yield and long stand life or the most profitable milk production? What would the milk production and financial impact on a dairy farm with a 25,000-pound herd average be if the best alfalfa now available was harvested at 50-100 percent bloom?

Two generations ago, dairy farmers cut at 10 percent bloom and then at 6-7 week intervals. Now, alfalfa is harvested at pre-bloom for at least the first three cuttings and more in longer season areas.

"With bud stage harvest, farmers will reap at least one more cutting per year," Thomas said. "Five cuttings are possible even in northern New York."

In summary, Thomas said quality trumps quantity, even if it involves some risks. The idea is milk per ton, not milk per acre.

Adjust mowing height to field conditions and ash concentrations, and make fall harvest decisions that are influenced by recent growing conditions, prior harvest management and how badly the forage is needed.

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