A Reality Check for Alfalfa Fields
Written by Ev Thomas and Dan Wiersma
|Look at the Roots
Count Stems, Not Plants
|The Right Time For Manure|
By now, most farmers have harvested their first and second cuttings of alfalfa and, therefore, should have some idea of the productivity of each field. This is regardless of whether each load of forage is weighed on drive-over scales (more common on larger dairy farms) or simply by counting loads.
If yields were disappointing, what was the reason? A rough winter for perennial forages, a dry spring, insect or disease problems, or something else?
Alfalfa is a perennial, but alfalfa plants won’t live indefinitely. Nature takes a toll through weather, insects, and diseases, but another reason alfalfa stands become depleted is crown damage by wheel traffic. Consider what runs across your alfalfa field during harvest: Mower, chopper or baler, multiple trips by trucks or forage wagons, manure and/or fertilizer spreaders, and perhaps a field sprayer, merger, or hay rake.
Then multiply the trips with harvest equipment by the number of harvests per season. By the time an alfalfa field has been harvested several times in a season, every plant in the field may have been run over at least once by the tires of a farm implement. Cornell University Forage Agronomist Jerry Cherney says that alfalfa persistence is influenced “by a series of small insults.” Among these “insults” is wheel traffic!
Look at the Roots
A good way to evaluate alfalfa stand health is by digging up plants in several areas of the field and examining the roots. You’ll need a shovel for this — don’t try to yank plants out of the ground.
Healthy roots will be solid white internally. Taproot injury normally starts at the crown and works its way down. You can often pick out these damaged plants early in the season because they’ll have less new growth.
Plants with brown, damaged areas in the crown and the top 1 to 2 inches of the taproot may remain productive for this season and perhaps one more year, but the clock is ticking. You should make plans to rotate the field to a crop other than alfalfa.
Count Stems, Not Plants
Agronomists once recommended counting alfalfa plants to predict yield potential, but a better method is to count stems. In pure stands of alfalfa, a field with an average of at least 55 stems per square foot is considered to have full yield potential. You can expect some yield loss with 40 to 50 stems per square foot; less than 40 and you should consider rotating the field to corn or another nonalfalfa crop.
If you grow alfalfa grass, you could still expect good yields with somewhat less than 40 alfalfa stems per square foot. Rules of thumb are tricky here, though, since the production potential would involve not only how much grass is present but also the species. Some grass species are more productive than others.
The ideal time to evaluate alfalfa stands is prior to first cut, but a summer evaluation can still be useful in suggesting future cropping plans. Many farmers are hesitant to replace moderately damaged stands early in the season since there’s so much other spring work to do, even though keeping an alfalfa stand with fewer than 40 stems per square foot may be a triumph of hope over experience. One advantage of a summer evaluation is that alfalfa plants with moderate injury may have produced some first-cut yield but then died as temperatures rose and the soil warmed and dried.
The Right Time For Manure
An alfalfa stand in its final year or two of production is a good candidate for summer manure application. Contrary to some long-held beliefs, manure doesn’t necessarily harm pure stands of alfalfa providing it’s applied soon after harvest. In fact, the nitrogen in manure may slightly improve alfalfa yield. The reason we don’t recommend applying nitrogen fertilizer to alfalfa is economics: The fertilizer would cost more than the value of the additional yield, and alfalfa can produce its own nitrogen.
As previously noted, wheel traffic may result in some plant damage, but this can be reduced by applying manure within three days of harvest. Research at Miner Institute found visible wheel track damage when manure application was delayed by seven days versus three days after alfalfa harvest. Forage ash content was also higher with the seven-day delay.
Among the best candidates for in-season manure application may be alfalfa grass fields in their second and later years after establishment. The nitrogen in the manure will elevate the yield of the forage grass.
Ev Thomas is retired from the William H. Miner Agricultural Research Institute and president of Oak Point Agronomics Ltd. Dan Wiersma is the alfalfa business manager with DuPont Pioneer.
Used by permission from the July 2016 issue of Hoard’s Dairyman. Copyright 2016 by W.D. Hoard & Sons Company, Fort Atkinson, Wisconsin.