This spring has brought an unusual combination of weather conditions, since we have been 5-10 degrees warmer than usual throughout April but are expecting cool weather at the start of May. We’ve also had the somewhat typical Ohio pattern of either no rain or two much rain depending on where you farm. This article will include information about forage moisture for stored forages, with a heavier emphasis on dry hay than baleage.
Different forages will respond to temperatures differently. Growing degree day accumulation affects the biomass of both grasses and legumes, and can also impact the development (flowering and head development) for grasses. Day length is more important than growing degree days for development (flowering) of alfalfa and other legumes. That’s great news for alfalfa producers this year, since the warm April weather encouraged growth before the longer days will trigger flower production. Be ready to harvest your grass hay earlier than normal this year, since the early head production associated with warm weather can decrease digestibility and protein in grasses.
When forages are cut, they generally have 70-85% moisture content. Developmental stage is the primary determinant of moisture at cutting, with cuttings before flower having >80% moisture and cuttings after seeds start forming having 70-75% moisture. But, extreme dry weather can also reduce at-cutting moisture levels. When the plant is first cut, it doesn’t yet know that it’s not growing anymore; it will continue to photosynthesize and release around 15% of its water through the stomatas on leaf surfaces. This process is primarily driven by sunlight, so forages cut with wide swath widths on a sunny day can get down to around 60% moisture in just a couple hours regardless of the air temperature—great for making baleage, which should be stored at 40-65% moisture.
Subsequent phases of drying can be more impacted by air temperature, especially since colder air can hold less moisture and hay drying slows dramatically when relative humidity is above 70%. Relative humidity is one of the driving factors of the drying process, and reducing relative humidity by 25% can cut dry time by about half.  The good news, though, is that sun intensity and wind speed are about as impactful as air temperature on drying speeds. So, don’t let cool weather deceive you—if there’s a breeze and some sun, your forages may dry just as fast as you’re used to.
Monitor forage moisture after cutting to begin baling at the right moisture for your storage system, since harvesting when forages are too wet can increase fire risk for dry hay storage and harvesting when forages are too dry can increase harvest losses. Generally, small square bales must be below 20% moisture for safe storage; large round bales should be low 18% and large square bales should be below 15% moisture. Â
For those of you experiencing wet weather this spring, preservatives are one tool that can help you make hay using smaller pockets of dry weather. Preservatives reduce bacterial growth, allowing safe storage of higher-moisture bales. No preservative has shown consistent efficacy above 30% moisture, but acid-based preservatives can be a useful tool around 25% moisture. Learn more about preservatives in this factsheet, and be sure to read all product labels carefully.
Other Resources:
Ohio Agronomy Guide:
https://extensionpubs.osu.edu/ohio-agronomy-guide-16th-edition-pdf/
Hay Preservatives Factsheet:
https://ohioline.osu.edu/factsheet/anr-0216
Baleage Factsheet:
https://forages.osu.edu/sites/forages/files/imce/2021%20Baleage%20factsheet.pdf
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