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Simple tips for determining 10 percent bloom in alfalfa

Ralph Whitesides for Progressive Forage Published on 11 July 2018
Determining percent in alfalfa bloom

In 1954, my grandfather bought a new International pickup truck to be used on the family farm. It was a unique green color and had all of the traditional features expected in a working farm truck.

I recall sitting in the middle of the bench seat with my grandfather on one side and my father on the other. We were looking over the alfalfa crop on the field we so accurately dubbed “sheep killer,” when I first heard the phrase: “The best-quality alfalfa is cut at 1/10th bloom.” What followed was a discussion about the interpretation of the phrase and how it applied to our field.

There had been a thunderstorm the previous evening, and the field was a beautiful green with a smattering of blue flowers showing up across it. Never leaving the cab of the truck, we eventually decided we could make an estimate of percent bloom by imagining all of the blue flowers moved to one area of the field and then estimating whether that area was the size of 10 percent of the field. We all gave it a try, and it became obvious our concept of 10 percent varied by age and experience.

Years later, while an undergraduate student at Utah State University, I learned alfalfa plants begin to flower first in some of the lowest leaf axils and, when you can actually see blossoms while sitting in a truck (or driving by a field at 30 to 50 mph), the stage of growth is already beyond 10 percent bloom. During the course of our professional careers, Earl Creech and I came to the conclusion it is possible to determine 10 percent bloom in an alfalfa field and, indeed, this is a good indicator for predicting reasonably good hay quality.

An outline of our suggested “old-school” approach for determining percent bloom in alfalfa fields follows:

  1. Know when to start looking – Historically, alfalfa harvest in most areas occurs about the same time each season: holiday season (wouldn’t you know …). In the Intermountain area of the West, especially the Great Basin, the first cutting of irrigated alfalfa usually takes place near Memorial Day (last few days of May or first days of June), the second cutting happens near the middle of July (in Utah, July 24th is a state holiday – Pioneer Day), and the third cutting begins somewhere near Labor Day

    (Alfalfa hay may be cut earlier than the holidays mentioned but, luckily for a lot of folks, hay hauling seems to correspond to the days that farm family youth are available.)

  2. Walk the field – When it is obvious hay harvest is likely to begin within a few weeks, take some time and walk the alfalfa fields. Look for flower buds and note whether any plants have already started to flower. Early flowers cannot be seen from a pickup and sometimes are not easily seen unless you look into the canopy and examine a few plants.

  3. Make a count – When it is obvious there are a few blossoms appearing in the field (based on the walk through the field), it is time to actually collect some samples and make an estimation of the percent bloom. This technique is most accurately accomplished by going to several areas in each field and selecting a representative spot to be sampled.

    When you have arrived at the test site, kneel in the alfalfa stand, close your eyes and reach out to randomly select 10 alfalfa stems. This is done most successfully if you reach in an arc and break off 10 stems of alfalfa. When you open your eyes, you can examine each stem for flowers. If one of 10 stems has flowers on it, then you have arrived at 10 percent bloom (higher math is a killer …).

Caution 1: Although this sounds like a very simple process, it is easy to cheat and hard to control personal bias. We have observed, when using this technique, most people kneel and scan the plants in front of them before closing their eyes. If they see a flower on any stem, they seem to unerringly select that stem when their eyes are closed. (We can only conclude most people think they are “winning” if they select the stem with the flowers …).

This undoubtedly introduces bias into the sample (and constitutes cheating …). Make a count in several areas of the field. Variations in soil type and irrigation patterns can cause plants in one area of the field to mature at different rates than others and thus influence 10 percent bloom estimates.

Caution 2: Walking through your fields and kneeling down, with your eyes closed for a few minutes at each stopping point, seems to have a definite impact on your religious standing in the community. Be prepared to provide advice/therapy to your neighbors as requested. (It’s OK to smile at this point in your reading.)

No matter how often you check your fields, count the flowering stems and determine the time to harvest, there is no stronger motivator to start cutting hay (erroneous as it may be) than when you see your neighbors greasing their swathers and driving into a field. Don’t rely on this method for determining your start date. There is little substitute for spending time in the field. Walking the fields and touching the plants makes it possible to understand when things are going well and when it is time to worry.  end mark

ILLUSTRATION: Illustration by Sarah Johnston.

Questions regarding this article can be directed to Earl Creech, an extension agronomist at Utah State University. He can be reached at Earl Creech.

Ralph Whitesides is a retired professor and extension weed specialist at Utah State University.

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