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Simple tool improves hay moisture test

With a compacted sample and an electronic tester, a more accurate moisture reading can be made in the field

Forage specialist Glenn Shewmaker demonstrates how to collect and place handfuls of hay samples in the tube. Pack the samples in tight and then insert the moisture sensor into the tube at different depths to get a field reading of hay moisture.

Packaging quality alfalfa hay can be a challenge. The hay industry is constantly pursuing new technologies to help the hay producer grow and package 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 ensuring leaf retention.

Today producers have hand-held moister testers, many large balers have high-quality onboard moisture-testing equipment, and more producers are applying preservative to hay to stretch the moisture window in order to maximize leaf retention and 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 producers know about determining the average moisture in the windrow, the better prepared they are to decide whether to bale. 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.

Electronic probes have limits

Another method is to 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 drier 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 per cent may actually be more than 30 per cent moisture when tested under the density conditions of the bale.

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

Undesirable reactions start when moisture and density increase beyond these levels. White mould decreases palatability and may also cause livestock to abort or deliver underdeveloped fetuses. Browning decreases palatability and increases acid detergent fibre (ADF) and acid detergent protein (ADP) to unacceptable levels. This high moisture and density accelerate 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 laboratory drying, Koster field drying, convection oven drying, and microwave oven drying. Determining the percentage moisture content of the sample using these techniques is based on the formula (wet forage weight minus dry forage weight) (divided by wet forage weight) (times 100). For example a 100-gram wet sample weighing 86 grams after drying would have 14 per cent 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 quickly. Convection oven drying takes 24 hours to run an adequate sample. Microwave ovens are fast, but the number of samples a producer can run at one time is limited and it is easy to burn the samples.

Collecting a compacted sample

In order to compensate for these constraints and come up with a more efficient method of testing samples, University of Idaho researchers Ron Thaemert and Glenn Shewmaker developed an inexpensive tool to replicate the compaction and density of the hay in a bale. It can be made with a few simple supplies from the local hardware store.

Windrow sampling tool

Materials needed:

  • 2 feet of 2-inch ABS pipe
  • 3 feet of 1-1/4-inch PVC pipe
  • 2, 1-1/4-inch PVC pipe caps
  • 2-inch ABS cleanout adapter
  • 2- inch ABS cleanout plug

To assemble the tool:

  • Glue the end caps on the 1-1/4-inch pipe to create a simulated plunger.
  • Glue the cleanout adapter on one end of the 2-inch ABS pipe.
  • Screw the 2-inch ABS cleanout plug into the adapter to create a simulated bale chamber.

“Selecting the correct location in the field for sampling is not as important as the number of samples that are taken,” says Shewmaker. “We suggest that you take at least 20 random samples for every 200-tons of hay across the whole spectrum of the field. This assures the producer that adequate representation of the entire field has been collected.”

Keep in mind that irregularities in the geography of a field will effect drying: windrows from low areas could be wetter while windrows from high open areas tend to be drier.

“The common practice of irrigation prior to harvest is less beneficial than previously thought,” says Shewmaker. “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.

Insert an electronic moisture probe into the hay in the collection tube and record the moisture readings from four levels of the collection chamber — four, eight, 12 and 16 inches in depth. Next, average the readings to obtain average moisture of the sample area. Continue the process across the remainder of the field and average the data from all of the samples.

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 maintain that the probe is calibrated correctly.

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