Testing hay moisture content—the percentage of water remaining in the forage after drying—is necessary before baling to prevent significant problems like the growth of mold and the loss of digestible nutrients. Baling hay when it is too wet can lead to excessive heating, which consumes dry matter. In extreme cases, high moisture can cause spontaneous combustion of hay stacks. Accurate measurement ensures the crop is preserved correctly, maintaining its nutritional value and preventing barn fires.
Target Moisture Levels for Safe Storage
The maximum safe moisture percentage for hay is not a single number; it varies based on the bale’s size and resulting density. Denser bales hold heat more effectively and allow less air circulation, meaning they require a lower moisture content to prevent spoilage. This difference dictates the threshold for safe baling and storage.
Small square bales, which are the least dense, can tolerate the highest moisture content, generally up to 20% moisture without significant risk of mold or heat damage if stored properly. Large round bales and large square bales are much denser and retain heat for longer periods, necessitating a lower maximum moisture level. These large packages should ideally be baled at 15% to 18% moisture to reduce the chance of excessive heating and mold development.
Baling hay above these recommended percentages increases the dry matter loss, which produces heat. If the internal bale temperature exceeds 120°F, quality loss accelerates. If it reaches 160°F or higher, the risk of fire becomes a serious concern. Hay intended for silage or haylage production is handled differently, where the goal is to promote fermentation, and moisture levels often range between 40% and 60%.
Instrumental Testing Methods
Electronic moisture meters provide the most rapid and quantitative assessment of hay moisture content, offering a numerical percentage reading in the field. These instruments function by measuring the electrical resistance within the hay sample, since water conducts electricity better than dry plant matter. The resistance measurement is then translated into a moisture percentage using internal calibration tables.
The most common type is the handheld probe meter, which features a long stainless steel probe designed to be inserted directly into loose hay or baled forage. When testing loose hay in the windrow, the hay must be compressed, often using a specialized windrow sampler or a bucket, to achieve a density that mimics a bale. Without sufficient compaction, the meter’s sensors cannot make proper contact with the forage, leading to inaccurate, often lower, readings.
To measure a freshly baled package, the probe should be inserted into the side of the bale, often at a 45-degree angle, making sure the tip reaches the center core. The operator must wait a few seconds for the reading to stabilize before recording the moisture percentage. Some advanced meters also monitor temperature, which is helpful for checking bales post-storage, as internal temperature spikes often follow high moisture content.
Less common for the average user, but available on high-capacity machinery, are in-chamber continuous monitoring systems. These sensors are mounted inside the baler chamber and provide real-time moisture feedback to the tractor cab as the hay is being processed. This continuous data allows the operator to adjust speed or apply preservative chemicals immediately, optimizing the baling process.
Non-Instrumental Field Tests
When an electronic meter is unavailable or a quick verification is needed, several practical, non-instrumental tests can provide an estimation of hay moisture. One straightforward technique is the Twist Test, where a small handful of hay is tightly twisted to check for the expulsion of moisture or sap. If any liquid is squeezed out, the hay is generally far too wet for safe baling, likely exceeding the 20% threshold.
The Scratch or Feel Test involves grasping a sample of hay and rubbing it between the hands to evaluate the condition of the leaves. Hay that is dry enough to bale will feel crisp, and the leaves may shatter easily. Hay that is too wet will feel soft and pliable. Excessive leaf shattering, however, indicates the hay may be too dry, resulting in nutrient loss due to brittle leaves breaking off.
A more involved, yet highly accurate, quantitative method is the Microwave Test. This process requires a microwave oven and an accurate scale to measure the weight loss from the sample due to water evaporation. A representative hay sample, typically around 100 grams, is weighed, then dried in the microwave using short intervals to prevent burning, with a cup of water placed inside to absorb excess energy. The sample is reweighed after each short drying cycle until the weight stops changing, indicating all moisture has been removed. The final dry weight is then used in a simple calculation to determine the exact moisture percentage.
Ensuring Sample Accuracy and Reliability
Relying on a single moisture reading is insufficient because moisture content is rarely uniform across an entire field or windrow. Variations occur due to differences in ground elevation, soil type, and exposure to sun and shade, which cause uneven drying. A good sampling strategy requires collecting at least 12 to 20 random samples across the entire area to ensure the data is representative.
When sampling, particular attention should be paid to areas that dry slowest, such as low spots, thicker parts of the windrow, and sections that were shaded during the day. The highest moisture reading obtained from these diverse locations often determines the safest time to begin baling. This focus on the “wettest spot” acts as a buffer against baling hay that will spoil once compressed.
For instrumental testing, meter maintenance and calibration checks are necessary. Electronic meters can be affected by ambient temperature, and some models require the user to manually input a temperature compensation setting to adjust the reading. Regular checks against a known standard or a highly accurate method like the microwave test help confirm the meter is performing within its stated accuracy range.