Predicting Pre-Harvest Alfalfa Quality with PEAQ

PEAQ stick to measure alfalfa qualityPredictive Equations for Alfalfa Quality (PEAQ)

Dodge County Forage Council (DCFC) will be doing the PEAQ stick (predictive equations for alfalfa) again for 2016. PEAQ  is a method to measure standing alfalfa’s forage quality before it’s harvested. Agronomists at the University of Wisconsin – Madison developed this method to help predict alfalfa’s Relative Feed Value (RFV) at the time of cutting.

Alfalfa height is measured using a wooden PEAQ measuring stick and an equation determines the alfalfa’s RFV. Values on opposite sides of the PEAQ stick correspond to alfalfa maturity stages. Increasing alfalfa Relative Feed Value adds value to farm enterprises through purchased feed reductions and increased dry matter intake. Determining when to cut first-crop alfalfa is often difficult because alfalfa quality, relative to flowering stage, varies greatly.

Estimate preharvest alfalfa quality using a PEAQ stick

Step 1: Choose a representative 2-square-foot area in the field.

Step 2: Determine the stage of the most mature stem in the area using the following criteria:

  • Vegetative: Stem is more than 12 inches tall with no visible buds or flowers.
  • Bud: Nodes have visible buds with no flowers or seed pods present.
  • Early flower: 1 or more nodes have open flowers.

Step 3: Select the tallest stem in the 2-square-foot area. Measure it on the correct maturity scale (from step 2) by placing the stick at the soil surface and determining RFQ at the tip of the stem (not the tip of the highest leaf). Note that the tallest stem may not be the most mature stem. Measure carefully, making sure the stick is next to stem.

Step 4: Repeat these three steps in five representative areas across the field. Sample more areas if fields are larger than 30 acres.

Producers are to take the readings on Monday and Thursday mornings and call the UW-Extension office by noon. The more producers that call in the more accurate we can predict the harvest window county wide. A full tally of reports will be put in the paper and reports on radio.

How PEAQ predicts forage quality

Research from Larry Tranel’s Cooperative Extension Service’s (CES)  fact sheet Sheet LT-111, says it’s important to note  that each point of RFV is typically worth about $1 per point on the alfalfa market and in dairy and livestock rations. It’s important to realize that first-crop alfalfa can rapidly drop 3-5 points of RFV per day as plants mature. Alfalfa quality should be 150 RFV for milking dairy herds and 120-130 RFV for heifers, stocker cattle and lactating beef cattle.

CES research shows that under the best conditions, 15% of forage dry matter will be lost at harvest (typically 15-25 RFV units). Therefore, research recommends cutting forage at 165 to 170 RFV to end up with harvested forage at 150 RFV. If it takes a week to harvest, consider starting even earlier.

Tranel’s fact sheet also illustrates that it’s important to note that grassy fields will reach the stated forage quality earlier than pure alfalfa. Alfalfa on lighter soils and southern slopes will also reach maturity faster. This procedure is most accurate for good stands of pure alfalfa with healthy growth.

Learn more

Forage resources are abailable at the UW-Extension Team Forage website at: http://fyi.uwex.edu/forage/alfalfa/. Dodge County UW-Extension and Dodge County Forage Council will continue weekly PEAQ readings through the first week in June. Dodge County PEAQ information is available at:http://dodge.uwex.edu/agriculture/forage-council/.

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