May 15, 2009

The most important weather factor affecting the rate of hay dry-down is sunlight. Temperature, humidity, wind speed, and soil moisture all are important, but solar radiation has the greatest impact on drying rate.

Research has shown as much as a 10-fold increase in drying rate as solar radiation changes from heavy cloud cover to full sunlight. No other factor affected drying rate even half as much.

While you can't control the amount of sunlight, you can take steps to use it to its full advantage:

• Watch weather reports and plan to cut hay during sunny weather. (Yes, this may be stating the obvious, but it's not always as easily done with hectic spring field work.)
• Spread your cut hay out in as wide a swath as possible. This will expose more of your hay to direct sunlight, enabling it to absorb as much energy from the sun as possible to evaporate moisture out of the hay. This may cause a little more sun bleaching than thick windrows, but fast dry-down is usually more valuable than green color.
• Mechanically conditioning your hay and turning it gently after the top gets dry will expose moister hay underneath and help hasten dry-down.

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Bruce Anderson
Extension Forage Specialist