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Many Factors Affect Alfalfa Harvest Decisions

NDSU’s dairy specialist offers alfalfa harvesting advice.

This year’s alfalfa hay harvest could be the earliest in years, according to J.W. Schroeder, North Dakota State University Extension Service dairy specialist.

Seeding surveys indicate that, unlike in the last five to six years, crops and forages are ahead of schedule this year.

“Naturally, the weather in the next few days could change that, but all indications at this point suggest that you could be done seeding early this year,” Schroeder says. “However, that doesn’t mean you have more time to put up forage, especially good-quality alfalfa for dairy cows.”

Many factors, such as environmental conditions, other fieldwork and insect infestations, enter into the decision of when to harvest alfalfa. But for dairy quality or prime alfalfa hay, height should be your guide, Schroeder advises.

“For years, we made forage harvest decisions based on plant maturity or calendar date,” he says. “Today plant height is more important in determining when to harvest first-cutting alfalfa than plant maturity and calendar date. Forage quality, digestibility and intake potential decrease with increasing maturity.”

A variable growing season changes the optimum time to take the first cutting from year to year, says Dwain Meyer, a professor and the interim chair of NDSU’s Plant Sciences Department. If spring is late and the temperature average is below normal, high-quality hay can be obtained by harvesting alfalfa at a later maturity stage, such as late bud to early bloom. For example, in 2008, the Red River Valley harvest started June 16.

However, if spring is early and above normal in temperature, the optimum harvest date will be earlier, as it was in 2002, when the first harvest was May 24.

Plant height is the best indicator of when to take the first harvest because relative feed value (RFV) and relative forage quality (RFQ) decrease as the plant height increases. The RFV decreases with increasing plant height at all maturity stages. For example, the RFV decreases 71 units at the late vegetative stage, 61 units at late bud stage and 53 units at the late flower stage when alfalfa increases from 20 to 40 inches in height. Therefore, the taller the plant, the earlier in plant maturity that harvest should occur to get prime hay (RFV greater than 151) in the bale.

According to NDSU research, harvest should begin whenever the alfalfa reaches about 28 inches in height, regardless of the maturity stage.

“If prime hay for feed or sale is the objective, then that means you need to get ready for an early start on the harvest in 2010,” Schroeder says. “But keep your target in mind, and be sure to allow another 25 to 30 units of RFV for harvesting losses. In other words, harvest will have to begin at 175 to 180 RFV to meet your target.”

The best method to estimate the RFV or RFQ in the first harvest is to use a PEAQ (Predictive Equations for Alfalfa Quality) stick available for purchase from the Midwest Forage Association (go to http://www.midwestforage.org/peaq.pdf), he says. It basically is a method to predict the forage quality of standing alfalfa using a calibrated stick.

Soil type and topography commonly affect height and maturity. Thus, alfalfa on hilltops has less growth and is more advanced in maturity than plants in lower, wetter areas of the field. Schroeder recommends basing harvesting decisions on the growth in the valleys because the short growth and more advanced maturity on the hilltops will not affect the quality extensively.

“Assuming that Mother Nature will provide ample moisture for subsequent forage harvests, keep in mind that second and third harvests are generally shorter in height than the first,” he says. “Therefore, the optimum maturity stage at harvest for these will be more advanced than the first harvest.”

The first harvest is always the most variable in maturity and, therefore, the least predictable, he notes. NDSU forage research found that under a four-cut system, the maturity at harvest generally is mid to late bud stage and occasionally 80 percent bloom stage (under drought stress) in the second harvest and 10 to 20 percent bloom stage in the third harvest or later under drought stress.

Once producers decide when to harvest, they also need to consider the time of day for the harvest. Research has shown that harvesting in late afternoon or early evening produces a forage with a higher total nonstructural carbohydrate content than one harvested in the morning due to the current day’s photosynthesis. Higher carbohydrate levels in the plant will increase digestibility, resulting in improved animal performance.

While plant height and scissor cutting reports from your area, if available, are the best indicators of when to start harvesting, do not leave plant maturity out of the harvesting decision, Schroeder says.

If the alfalfa is for lactating dairy cows, it should be harvested at about 160 RFV, or when it has about a 37 to 38 percent neutral detergent fiber (NDF). The crude protein content in alfalfa of this quality will be about 20 percent. For wet forages, the haylage dry matter of 40 to 45 percent is ideal.

Don’t overlook particle length of the haylage, Schroeder says. Cattle still need some length of chop to stimulate chewing. Determine your effective fiber by using the Penn State forage particle box to measure the chop length of the alfalfa a couple of times each harvest day. Forage particle boxes are available from Nasco at http://www.enasco.com/.

The objective is to have 15 to 20 percent of the chopped alfalfa by weight still remaining on the top screen. Haylage can become gummy and sticky, so make sure you shake wet samples well and look carefully at the material on the top screen to see that it contains stems and not a mat of wet haylage.

Harvest still should occur at 26 to 28 inches in height, Schroeder says.

“If we continue with warm and dry weather this spring, alfalfa plants will mature early and, therefore, the alfalfa plant will become more advanced than anticipated,” he adds. “The amount of fiber and lignin in the alfalfa plant that affects forage quality is related more to plant height than plant maturity. Since all indications are this spring will stay warm, plant maturity/height will sneak up on us faster than expected. For example, alfalfa plants on Fargo research plots already were 12 to 14 inches in height on May 3. Don’t be surprised if you see alfalfa in the swath by Memorial Day.”

Schroeder also offers these notes of caution: The relationship between height and quality was developed in pure alfalfa stands, so quality estimates in alfalfa-grass fields based on just alfalfa will be less reliable. Furthermore, frost still is possible. The good news is that a light frost (29 F) is not a concern. However, if temperatures get below 23 F, then losses would be likely.

“So before you put off the alfalfa harvest because you think it is too early, or you still need to service the chopper, check those fields for height and maturity,” he says.


NDSU Agriculture Communication

Source:J.W. Schroeder, (701) 231-7663, jw.schroeder@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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