Forage: When to Harvest

By Dr. Harold Willis

Now that you have a good stand of forage established and understand some principles of fertilization to obtain high quality, how can the stand be best managed to give optimal yields of the highest quality feed?


When to cut

There have been various ways used over the years to tell when to cut alfalfa, such as cutting at the bud stage, or at 10% bloom or half bloom, or full bloom, or when new shoots appear from the crown, or even by the calendar. The latter is obviously unreliable because of variable weather conditions, but when should alfalfa be cut? There are scientific studies which show that the plant’s content of minerals and digestible nutrients is highest during the succulent growth stage and declines during flowering and maturity, while fiber content increases. Feed value is said to decrease.

These studies were probably done with forages that were fertilized with too much potassium and perhaps other imbalances, because on-the-farm experience and certified production records show that top quality feed can be produced when alfalfa is not cut until early bloom (25 – 50% bloom). Cows can eat two-thirds to one-half as much of this kind of hay and still increase in production. Early-cut hay is often too high in nitrates and low in high quality protein.

Traditional studies have shown that the long-range greatest yields and best recovery growth are produced when alfalfa is cut at full bloom, although in the Southwest, greater yields may be obtained if cutting is done at 10% bloom (first bloom), but in the hottest weather stand density and yield will be reduced.

The best method to judge when to cut is to use a refractometer to measure the sugar content of plant juice every day or two as blooms begin to appear. When the sugar readings reach a peak or begin to level off, that is the time to cut. That is generally at 25 – 50% bloom. The appearance of new shoots from the crown is another sign to watch for, but is not as reliable as bloom stage or the use of a refractometer.

Alfalfa blossoms
Alfalfa in bloom.

Signs of quality

When you begin to get your soil fertility in the proper balance (high calcium and phosphorus, low potassium), you will be amazed that your alfalfa doesn’t bloom at a height of 8 inches or a foot like it used to, but it will keep on growing—and growing—and growing. It may reach heights of over 40 or 50 inches before it is ready to cut. And it will be so thick that you may have to get a new heavy-duty mower! You won’t get as many cuttings as your neighbor does, but you will get far superior quality feed and probably as good or better total yields.

If you cut open several stems with a knife, you may begin to see the growth of “solid stem alfalfa,” in which the entire stem is filled with
succulent cells, not air.

Good quality hay will dry rapidly after cutting (because its cells contain more minerals and nutrients and less water) and can even be baled so wet that ordinary hay would heat up and burn the barn down.

Cutting

Cutting should be done with a sickle-bar or cutter-bar mower, which gives a good, clean cut to the stems. High quality hay will dry quickly and does not need to be crushed or crimped; in fact, this torture treatment can cause loss of nutrients from the crushed tissues. Cutting should always be made above any new shoots that are sprouting from the crown, since the growing point of legumes is at the stem tips, and cutting them will severely retard the next growth. This is not true of grasses, whose growing point is at or below ground level.

Drying aids

If you want to speed drying, there are sprays that can be used. Some are designed for poor quality forage and are basically a salt solution, but there are also ways of speeding drying and increasing the feed value of hay by spraying a carbohydrate solution before cutting.

Stimulate regrowth

If the soil needs any nitrogen, a nitrate-containing fertilizer can be topdressed at a low rate after a cutting to stimulate regrowth. Fertilizers containing ammonium nitrogen should not be used because ammonium will stimulate early flowering rather than vegetative growth (leaves and stems).

Also, if you did not apply the recommended lime and soft rock phosphate before seeding or in the fall or spring, they can be topdressed after a cutting.

Early cuttings

The first cutting of a new stand should be delayed until the plants are strong and vigorous and have a good root system, generally 70 to 90 days after germination for a spring seeding. Also, in the North the first cutting should not be made at an early stage of growth or the plants will be injured from low food reserves.

Late cuttings

In more northern regions especially, alfalfa should not be cut or grazed during the period of 4 to 6 weeks before the first killing frost, or approximately between the first week of September and mid-October. This is so the plants can store up enough food reserves to survive the winter. A cutting can be made after a killing frost (not a light frost).

Source: How to Grow Great Alfalfa