Do hay drying agents and preservatives pay? In the Midwest, at least, the answer is "yes" for drying agents, "maybe" for preservatives.

Both can reduce the risk of rain damage by helping growers get alfalfa off the field faster. And USDA-ARS research at Michigan State University shows a positive return on investment for routine drying-agent use -- even if the hay sometimes would escape rain without them.

But the same research indicates that preservative application is a paying proposition only if the hay is 30% moisture or less and rain is imminent.

The Michigan research was done by ag engineer Al Rotz, now at USDA's Pasture Systems and Watershed Management Research Laboratories in University Park, PA.

Rotz found that drying agents -- sodium carbonate and/or potassium carbonate applied at the time of cutting -- can reduce alfalfa's drying time by 50-70% under good drying conditions.

He also observed that drying agents were twice as effective when alfalfa was laid in wide swaths instead of windrows.

They're more effective in the second and third cuttings than in the first, too, says Rotz. He figures that's because the first-cutting yield is higher and less chemical usually is applied per ton. The higher yield also produces bigger swaths, making drying more difficult.

In addition, cooler temperatures during the first cutting may reduce a drying agent's effectiveness. Laboratory drying tests show that chemical treatments are most effective at temperatures around 80 1/4.

"You have to have good drying conditions to make the agents work," says Rotz.

Hay preservatives such as propionic acid inhibit or kill microorganisms that can spoil damp hay. Harvest losses are lower when hay is baled at higher-than-normal moisture levels. But preservatives aren't economical unless the crop otherwise would be rain-damaged, says Bill Weiss, Ohio State University dairy scientist.

For example, baling hay at 25% moisture, compared to 20%, increases yields about 2%. But the small yield gain isn't enough to pay for a preservative, says Weiss. So if rain isn't likely for a few days after cutting, spending $5-10/acre for a preservative could be a losing proposition, he adds.

However, if weather forecasters predict a 100% chance of showers, the story changes. When the hay is nearly ready to bale and rain is imminent, preservatives are economical.

A preservative pays a 3:1 return on investment when it prevents rain damage. Damaged hay can lose up to one-third of its digestible dry matter. Digestible crude protein losses can also be great.

To find out how effective a preservative may be, check its label. Don't use a product if it has less than 50% propionic acid, caution North Dakota State University extension specialists.

They recommend applying propionic acid at 20 lbs per ton of 25%-moisture hay. More is needed for wetter hay. But hay higher than 30% moisture should not be baled, even with a preservative, says Weiss.