CFAES Give Today
OSU Extension

College of Food, Agricultural, and Environmental Sciences

May 19, 2020 - 8:00am --

Forage maturity/stage of development is often cited as the number one factor that determines forage quality, but for any stored forage, moisture content at harvest is a close second. Moisture content drives what happens to that forage after it is removed from the field, whether quality is maintained or degraded. Improper moisture content can reduce storage life.

The most common method of determining forage moisture is some type of visual appraisal whereby a forage sample is either twisted together or squeezed into a ball and then released.  How quickly that twisted sample unravels, or the ball falls apart determines if the forage is too wet, too dry, or ready for harvest.  While a lot of good quality stored forage has been made using this method, errors sometimes get made and forage quality is compromised, or forage is lost.  For those producers looking for more certainty in determining forage moisture there are some tools available that can help.

Tools available to determine forage moisture include a microwave oven, commercial forage moisture testers, hand-constructed vortex dryers, air fryers, moisture probes, and moisture sensors built into harvest equipment.  Each has some advantages and disadvantages, but each used with the proper knowledge and protocol can help the forage producer more accurately determine forage moisture.  Most of these tools requires that a good representative sample be collected to produce a reliable result.  When sampling windrows be sure to sample the entire cross section (top, middle, and bottom) from multiple areas of the field.

Microwaves are commonly available, and you can get one at a reasonable cost. Microwaves provide forage moisture determination to within 1-2% of actual forage moisture in about 20 minutes.  The biggest drawback to using a microwave is that the forage material can catch on fire if the sampler is not being careful as the forage dries down to its endpoint moisture.  The procedure involves weighing out 100 grams (fresh weight) of a representative forage sample that has been cut into pieces no larger than one inch in length.  Basically, you continue to cook the sample in small time increments, removing and weighing the sample until its weight does not change by more than one gram.  If you start with 100 grams and the end weight is 20 grams, the moisture content of the forage is 80%.  For anyone who wants more details on the procedure, contact me at the Wayne County Extension office.

Commercial forage moisture testers use either heat or electrical conductivity to come up with a moisture reading.  Heat type testers include a heating unit and a fan.  They determine moisture content by forcing heated air through a forage sample of known weight.  Unlike a microwave, they do not require constant supervision/monitoring.  Depending upon the initial forage moisture the process takes 25 to 35 minutes.  Accuracy is within 3% of oven dried samples.  Forage samples should be in pieces that are 1-2 inches in length. The advantage over a microwave is that the risk of setting fire to the sample is reduced. For many producers, the biggest disadvantage of this type of tester is the cost.  Depending upon the make and model, count on spending about $350 to $450.

The vortex dryer was developed by Penn State Extension. It uses a common hand-held hair dryer, some CPVC tubing, some galvanized steel, a furnace filter, window screen, and some plywood.  Cost will be approximately $50-$60 to assemble in the farm shop.  Forage sample size in the vortex dryer is 200 grams.  The procedure is basically the same as with a microwave oven, starting with an initial weight and drying the sample until weight does not change more than one gram.  Accuracy is within 1% of a drying oven.  Hay samples will take 20-25 minutes to dry, while forage silage/corn silage samples can take 40 to 60 minutes to get a final moisture determination.  More information about assembling and using the vortex dryer is available at

Recently, I was made aware that some producers are using kitchen air fryers with great success in determining forage moisture.  Cost is in the $100 dollar range.  They come with variable temperature settings.  To determine forage moisture, use a temperature range from 200 to 250 degrees.   It will take about 25 minutes to dry a 100-gram sample.  Samples will not accidently catch on fire and another advantage is that fines are trapped, so doing a moisture determination of a total mixed ration (TMR) sample provides more accurate results. Here is a link to a January 2019 Progressive Forage article on using an air fryer to determine moisture content:

Forage moisture testers that use electrical conductivity include probes as well as sensors mounted on balers/harvest equipment.  The advantage of these types of testers is that they provide near instantaneous moisture readings.  Cost is a factor.  Depending upon the model of the tester probe, they can cost anywhere from $180 to $300 or more.  Sensors on your baler or harvesting equipment may add $275-400 to the price tag. For the most advanced systems that can mark hi-moisture bales the cost can be over $1000 or when systems also manage variable rate preservative application, cost can be over $2500. Depending on the system, the accuracy may only be ±5%.  Sensors on balers and harvesting equipment begin to lose accuracy and reliability as forage material over time leaves gummy residues on the sensor.  Periodic cleaning and calibration of the sensor is needed to maintain accurate readings.

Contact the Wayne County Extension office at 330-264-8722 for more information or read a more complete article on the topic online at