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Windrow moisture testing made easy

Michael J. Thomas for Progressive Forage Grower Published on 30 March 2016
Insert hay into testing tube

Producing dairy quality alfalfa hay has always been a challenge. The industry is constantly pursuing new technologies to help the hay producer grow and package a consistently high-quality forage.

Machinery design has advanced in order to handle the hay as delicately as possible to minimize leaf loss. But even with these advances, the proper moisture level is still the most effective means of insuring leaf retention.

Today producers are equipped with hand-held moisture testers; many large balers have high-quality on-board moisture testing equipment, and more producers are applying preservative to the hay to stretch the moisture window in order to maximize leaf retention and still maintain storage quality.

Despite all of these tools at our disposal, a producer is still faced with the dilemma of determining the stem moisture of the hay in the windrow across the entire field: too dry and you lose quality to leaf shatter, too wet and you cannot compensate with enough preservative or it becomes cost-prohibitive to apply enough to offset damage or fire.

The more a producer knows about determining the average moisture in the windrow, the better prepared he is to make a baling readiness decision.

The age-old method of twisting a handful of alfalfa until it breaks is a good way to know the hay is dry enough to bale, but unfortunately by the time the hay is dry enough to break by this method it is too dry for good leaf retention – without a heavy dew.

Place collection chamber on the ground, use smaller tube as a plunger

Some producers today insert an electronic moisture probe into a handful of alfalfa from the underside of sample windrows to get an idea of the moisture. While this is a step up from the twist test, the probe will tend to provide data suggesting the hay is dryer than it actually may be.

Electronic moisture probes function by passing an electric current through two brass contacts on the shaft and analyzing the conductivity. This conductivity is affected by the density of the material the current is passed through. A loose handful of hay that tests 14 percent may actually be over 30 percent moisture when tested under the density conditions of the bale.

The relationship between bale size, moisture content and density is very important. Small 16 x 18-inch bales can safely contain 18 to 20 percent moisture, half-ton bales 14 to 16 percent and 1-ton bales should not exceed 12 to 14 percent moisture.

As moisture and density increase beyond these levels, undesirable reactions occur. White mold causes palatability to decrease and may also cause livestock to abort or deliver underdeveloped fetuses. Browning decreases palatability and increases acid detergent fiber (ADF) and acid detergent protein (ADP) to unacceptable levels.

This high moisture and density accelerates microbial growth. The microbes consume sugars and starches, leaving behind the structural carbohydrates, cellulose and lignin, which make up ADF. The heat generated by this process also damages some protein, reported as ADP, causing it to be indigestible by livestock.

To accurately test moisture samples in the past, producers relied on the following methods: laboratory drying, Koster field drying, convection oven drying and microwave oven drying. Determining the moisture content of the sample using these techniques is based on the following formula:

(Wet forage weight – dry forage weight/wet forage weight) x 100 = Percent windrow moisture

These methods are very accurate and still should be used to calibrate electronic moisture probes, but they have limiting factors that make them undesirable to producers.

It could take days to get the results of a lab test, a Koster field dryer requires a portable generator and several units are necessary to test multiple samples in a timely manner, convection oven drying takes 24 hours to run an adequate sample, and microwave ovens are fast, but the number of samples a producer can run at one time are limited and it is easy to burn the samples.

Use the smaller tube to compress the hay

In order to compensate for these limiting constraints and come up with a more efficient method of testing samples, two University of Idaho researchers: Ron Thaemert, Blaine County extension educator, and Glenn Shewmaker, forage specialist with University of Idaho – Twin Falls Research and Extension Center, performed a study and developed an inexpensive tool that can be made with a few simple supplies from the local hardware store to replicate the compaction and density of the hay in a bale.

Windrow sampling tool materials needed:

2 feet of 2-inch ABS pipe
3 feet of 1.25-inch PVC pipe
Two 1.25-inch PVC pipe caps
2-inch ABS cleanout adapter
2-inch ABS cleanout plug

Assemble the tool by gluing the end caps on the 1.25-inch pipe forming a simulated plunger. Next, glue the cleanout adapter on one end of the 2-inch ABS pipe.

Screw the 2-inch ABS cleanout plug into the adapter, forming a simulation of a bale chamber – and you are ready to moisture test alfalfa in a windrow.

Shewmaker says, “Selecting the correct location in the field for sampling is not as important as the number of samples that are taken. We suggest that you take at least 20 random samples per 200 ton of hay across the whole spectrum of the field.

This assures the producer that adequate representation of the entire field has been collected.”

Bear in mind that irregularities in the geography of a field will affect drying – windrows from low areas could be wetter, while windrows from high open areas tend to be dryer.

Also, Thaemert says, “The common practice of irrigation prior to harvest is less beneficial than previously thought. Not only is soil compaction increased, but drying time is increased by placing a wet alfalfa windrow on wet soil.”

Once a sample location is selected, turn a portion of the windrow over and feel for the dampest hay in the sample area. Insert this hay into the testing tool a handful at a time until the tube is full.

Place the collection chamber on the ground with the capped end down and use the smaller tube (plunger) to compress the hay in the collection chamber, simulating the compaction of baled hay.

record electronic moisture reading from four levels of the collection chamber

Record electronic moisture readings from four levels of the collection chamber and average the readings at 4-, 8-, 12-, and 16-inch depths. Continue the process across the remainder of the field and average the data from all of the samples.

“You have now gathered ample moisture samples on which you can confidently base your baling readiness decision,” says Shewmaker.

Care should be taken to clean the electronic probe after a few samples have been taken. As residue builds up on the probe it begins to reduce the accuracy of the reading. Also, probe readings should be compared to oven samples periodically to verify that the probe is calibrated correctly.  FG

Michael J. Thomas is a freelancer based in Idaho.

PHOTO 1: Turn a portion of the windrow over and feel for the dampest hay in the sample area. Insert this hay into the testing tool a handful at a time until the tube is full.

PHOTO 2: Place the collection chamber on the ground with the capped end down and use the smaller tube (plunger) to compress the hay in the collection chamber. 

PHOTO 3: Use the smaller tube (plunger) to compress the hay in the collection chamber, simulating baler action.

PHOTO 4: Record electronic moisture readings from four levels of the collection chamber and average the readings at 4-, 8-, 12- and 16-inch depths. Continue the process across the remainder of the field and average the data from all of the samples. Photos provided by Glenn Shewmaker.

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