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Harvesting Prime Alfalfa Hay
Deciding when to harvest alfalfa to get prime hay is not an easy decision. Prime hay is defined as having a relative feed value (RFV) greater than 151.
Dr. Ken Albrecht of the USDA Dairy Lab in Madison, Wisconsin developed the PEAQ (Predication Equations for Alfalfa Quality) system in the early 1990s. This system is a more reliable method of estimating forage quality of alfalfa in the field. The PEAQ system is based on observing and/or measuring two alfalfa growth characteristics within a target area of the field, the most mature stem and the tallest stem. The tallest stem may or may not be the most mature stem, but is merely measured to the nearest inch. The maturity stage is determined used the following.:
Late vegetative... Stem is more than 12 inches tall, but no visible flowers
Early bud ... One to two nodes have viable buds, no visible flowers open
Late bud... More than two nodes have visible buds, no visible flowers open
Early flower... One node with at least one open flower
Late flower... Two or more nodes have open flowers
The PEAQ system estimates the forage quality of alfalfa standing in the field. To obtain greater than 151 RFV in the bale, harvest must begin when the PEAQ system estimates the forage quality at 175 to 180, since harvesting losses will reduce the quality of the final product.
To illustrate how important the height of the tallest stem (the canopy in general) is in determining forage quality, see the following table:
|
Height of Tallest Stem |
Late Vegetative |
Early Bud |
Late Bud |
Early Flower |
Late Flower |
|
(inches) |
----------Relative Feed Value ----------- |
||||
|
20 |
213 |
201 |
191 |
181 |
171 |
|
25 |
191 |
181 |
172 |
163 |
155 |
|
30 |
173 |
164 |
156 |
148 |
141 |
|
35 |
156 |
149 |
142 |
135 |
129 |
The RFV decreases with increasing maturity, which is a long-known principle of forage quality effects. However, note that the RFV decreases with increasing height more than with increasing maturity! Even if the PEAQ system is not totally accurate, plant height must be taken into consideration when determining the optimum stage to harvest the alfalfa.
Under irrigation, the first harvest will grow to 30 to 36 inches tall depending on the particular year (temperature and date growth initiated). If you check in the table, note that harvest must begin in the last vegetative stage if prime hay is to be harvested in the first harvest! Most producers are not harvesting the first cutting early enough to obtain prime hay. Conversely, irrigated alfalfa will grow to about 20 to 25 inches in the third harvest. If the alfalfa is only 20 inches tall, harvest can wait until nearly 50 percent bloom and still expect prime hay in the bale. waiting to 50 percent bloom will increase the forage yield partially offsetting that lost by the early first harvest.
Use the height of the alfalfa to make the decision when to harvest alfalfa. The taller the plant, the earlier harvest must being to obtain prime hay. The shorter the plant, the more advanced maturity can be and still expect prime hay in the bale.
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