Grain & Hay Moisture Meters | Protecting the Harvest

hay moisture meter

While the weeks and months leading up to harvest time are important for realizing a crop, the weeks and months immediately after mean just as much.

This is especially true for two crops meant to have a long shelf life: hay and grains.

Like the inside of a building, one of the biggest threats to both products of the field is moisture. 

Too much or too little moisture can spoil hay and grain in some fashion, resulting in a loss of both quality and quantity.

For farmers planning to sell their crops immediately or store them for future use, keeping close tabs on moisture levels of harvested hay and grains matters.

In this article, we'll look at:

  • Mosture's relationship with both crops
  • Testing moisture levels in hay
  • Testing moisture levels in grain
  • & much more

Moisture Content & Hay and Grain

From the day their seeds are sown to when their final products are sold or used, hay and grain have a close relationship with moisture.

The most obvious reason – moisture helps both grow and thrive in the field. However, once harvested, moisture presence and the way both crops interact with it take a different turn.

With hay, moisture presence is a double-edged sword. On one hand, an appropriate amount of moisture (hay 18 - 22% or less/Straw less than 20%) helps preserve the nutritional value of the crop for livestock. At the same time, too much moisture lends itself to supporting different organisms – bacteria and mold. Not only do both ruin a bale of hay, but they also have the potential to cause more damage. In extreme cases, the heat generated by microbial activity can be enough to start a fire that can spread quickly through nearby bales.

The story is much the same with grain, however, it does get a bit more complex.

Like hay, grain needs an appropriate amount of moisture to maintain nutritional values. And at the same time, too much moisture creates a welcoming environment for bacteria and mold.

The difference in grain's relationship with moisture is two-fold:

  1. Grains have different acceptable levels of moisture (this isn't dissimilar to how different species of wood have varying acceptable moisture levels):

    Grain Type Acceptable Moisture Level 

    15% or less

    Barley  20-30%
    Wheat 14-20%
    Oats 12.5% or less
    Canola 10% or less
    Soya 10-15%
    Rice  10-15%
    Oilseed Rape 

    8% or less


    12% or less


    14% or less


    9% or less


    12% or less


    20% or less


    14% or less


    12% or less


  2. When within an acceptable range, grain needs to retain the moisture it has as the crop is sold by weight. It's simple economics – a lower weight means lower profit-per-bushel.

Regardless of the grain or hay, preserving and protecting both harvest crops is largely dependent on finding and maintaining a healthy balance with moisture. And that requires regularly checking moisture levels and making adjustments as need be.

[How to] Checking Moisture Levels in Hay and Grain

Like inspecting the inside of a building, testing both hay and grains for moisture is a straightforward process. And there are several ways to conduct tests.

The most efficient method that provides immediate results is using digital moisture meters made for testing hay and grains.

Let's dig into how to complete moisture meter tests on both harvests.

balemater_with_probe_in_straw_smallTesting Hay Bales for Moisture

The same way a home inspector uses their moisture meter with an extension probe on walls and other materials, the digital probes of a hay bale moisture meter are used to test hay bales from the inside.

After selecting several hay bales to test and turning on your hay moisture meter, it's as simple as:

  1. Inserting the hay moisture meter’s probe into the bale: Take the moisture meter and insert the probe or prongs into the bale. It's best to insert the probe in the center of the bale where moisture tends to be higher. Push it in as far as necessary to obtain an accurate reading.
  2. Allow the reading to stabilize: Give the moisture meter a few seconds to stabilize and provide an accurate reading.
  3. Repeat the process: Test multiple bales to account for any variations in moisture content within the lot.
  4. Calculate the average moisture content: Add up the moisture content readings from all the bales tested and divide by the total number of bales tested to determine the overall average for the lot.

Remember: harvest hay should have a moisture content reading of no more than 22%.

 Just as there's no one way to grow a crop, there's no singular way to keep tabs on moisture levels within a harvest. Other moisture testing methods commonly used to check hay and grain for moisture include:

          1. Oven Drying Method – which involves drying a sample of the grain or hay in an oven at a specific temperature for a set period of time. You'll need to record both the pre-dry and post-dry weights of the same and calculate the percent difference between both to determine moisture content. The same type of test can be completed using a microwave, too.
          2. Chemical Testing – which involves using a chemical reagent to react with the water in a grain or hay sample to produce a color change, which can be compared to a chart to determine the moisture content



Caveat: Bale Shape

Hay bales come in a few different shapes and sizes, and this does affect the moisture content within, especially if left unprotected from the elements.

  • Rectangular/Square Bales: The most emblematic bale shape, these bales have flat surfaces and well-defined edges. If left uncovered in the field, their shape doesn't allow for efficient rainwater or moisture runoff as its surfaces are flat. If you're testing rectangular bales, it's best to check for moisture on all four sides. These bales should have between 18-22% moisture content.
  • Large Square Bales: A close relative to the previous bale shape, are as they sound: bigger. Their larger surface makes them more susceptible to moisture retention if not stored properly. What's more, if they're stored in contact with the ground or exposed to rain, the larger surface area increases the chances of water absorption, leading to higher moisture content. This bale type should have a moisture content of between 12-16%.
  • Round Bales: These cylindrical bales have become commonplace in many parts of the world. Unlike its flat-surfaced counterparts, round bales have a natural runoff shape which allows rainwater and other sources of moisture to move off quickly – However, the ends of round bales are more susceptible to water penetration, especially if they are not stored properly or covered. Round bales are also more dense and compacted. Their moisture readings should be between 15-20%.



Testing Grain for Moisture

Again, grain is similar to hay, but there are some differences.

In an identical process to testing hay, you can measure moisture in grain by using a moisture meter with an extension probe.

However, the best way to test grain for moisture is with the ground grain method.

Instead of measuring the moisture directly in whole grain kernels, this method involves grinding the grain into a crumb  and running an electrical current through it to measure resistances. As water is conductive, the less resistance the more moist the grain is.

No matter which method you use, your grain meter will need to be calibrated to the type of grain it's testing and it's best to test several samples to get a broader representation of moisture content.


The GrainMaster makes ground grain moisture testing a simple and fast process:


The #1 Way to Control Moisture in Hay and Grain

No matter which grain or hay you're dealing with, the most effective way to control and manage moisture levels is by being informed. By that we mean regularly testing both harvested crops.

Simply put – moisture testing is not a "one and done" ordeal when it comes to hay and grain. A variety of environmental factors can change moisture presence within each harvest, especially as the crop is stored for long periods of time. Even indoors, changes in ambient conditions, such as relative humidity, have a direct impact on, say, a bale of hay.

Left unchecked, excessive moisture can lead to a host of problems for a harvested crop, making months of hard work and patience go to waste.

Agriculture Moisture Meters: Preserving the Harvest in Multiple Ways

No matter how many bales of hay or bushels of grain you harvest at the end of a long growing season, there's nothing like seeing your hard work quite literally pay off. The last thing a farmer wants is to see a crop lost.

With the right moisture meters, keeping track of moisture presence within hay and grains is simple, helping you take one more important step toward making every harvest one that pays dividends.

Find Your Meter

Browse our selection of moisture meters – and be sure to check out our BailMaster and GrainMaster i2

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