Keeping track of your alfalfa plants’ height is the best way to tell when to take off your first cutting, says J.W. Schroeder, North Dakota State University Extension dairy specialist.

“For years, we made forage harvest decisions based on plant maturity or calendar date. Today plant height is more important in determining when to harvest first-cutting alfalfa,” he says.

As plant height increases, relative feed value (RFV) and relative forage quality (RFQ) decrease. RFV decreases at all maturity stages: 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” in height. So the taller the plant, the earlier in plant maturity that harvest should occur to get prime hay (greater than 151 RFV) in the bale.

Begin harvest whenever alfalfa reaches about 28” in height, regardless of maturity stage, according to NDSU research.

“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 25-30 units of RFV for harvesting losses. In other words, harvest will have to begin at 175-180 RFV to meet your target.”

To estimate first-harvest RFV or RFQ, use a PEAQ (Predictive Equations for Alfalfa Quality) stick, which can be bought from the Midwest Forage Association, he suggests. The calibrated stick basically predicts forage quality of standing alfalfa.

Of course, height and maturity are affected by soil type and topography; alfalfa on hilltops has less growth and is more advanced in maturity than alfalfa in lower, wetter areas of fields. Schroeder recommends basing harvesting decisions on growth in valleys because the short hilltop growth and more advanced maturity won’t affect 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’s.”

Forage harvested in late afternoon or early evening produces a higher total nonstructural carbohydrate content than that harvested in the morning, Schroeder says. That increases digestibility and improves animal performance.

Growers shouldn’t disregard plant maturity before deciding when to harvest, Schroeder adds. Alfalfa for lactating dairy cows should be harvested at about 160 RFV, or when it has about 37-38% NDF and 20% crude protein. For haylage, a dry matter of 40-45% is ideal.

Determine your haylage’s effective fiber and particle length by using a Penn State forage particle separator, available from Nasco at About 15-20% of the chopped alfalfa by weight should remain on the top screen. Shake wet samples well and look carefully at the material on top screen to see that it contains stems and not matted, wet haylage, Schroeder adds.

“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 says. “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 that 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 12-14” in height on May 3. Don’t be surprised if you see alfalfa in the swath by Memorial Day.”

Schroeder also cautions growers to remember that making quality estimates in alfalfa-grass fields will be less reliable and that frost damage still is possible. If temperatures get below 23ºF, losses are 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.”