Producers managing around “chance of showers” weather need to take into account these different effects of rainfall on hay, says J.W. Schroeder, North Dakota State University extension dairy specialist.

Rain causes decreases in hay value by leaching the soluble plant nutrients in the leaves. Rain also results in leaf loss from shattering caused by additional tedding or raking; bleaching or browning, which affects price; and molds, bacteria and yeasts that consume the soluble carbohydrates while the forage is lying in the windrow. The period when the rain reaches the forage, how hard the rain falls and how long it lasts can affect forage quality and quantity, too.

Forage rained on shortly after mowing has fewer negative effects than hay that is almost fit and then rained on again. Obviously, a short-duration rain causes less leaching than a long-duration rain event, but research also has shown that given the same amount of rainfall, the shorter, more intense rain event would leach more soluble compounds from the leaves than a longer, more gentle rain.

The risk of rain damage to the hay crop is substantial. One rain shower of about 1 inch on hay during curing can cause yield losses of greater than 5 percent, reduce total digestible nutrients by 5 to 6 percent and reduce dry-matter intake by 8 to 9 percent.

In the more arid areas of the United States., the risk of rain damage is lower because of the abundant sunlight, low humidity levels and rarity of rainfall that allow for a rapid drying rate for hay crops (often less than two days).

“However, in areas where humidity is a problem, as we are experiencing in much of North Dakota, drying a hay crop to the moisture level that is safe for hay storage (15 to 16 percent for large round or big square bales, 17 to 18 percent for small square bales) may take more than five days,” says Schroeder.

Unfortunately, the chances have been high that a significant rain event will occur during any given five-day stretch. To make matters worse, the high humidity and the condensation of dew actually can cause the moisture of the partially cured hay to increase overnight. Consequently, drying hay as quickly as possible is critical.

The following recommendations can help ensure hay drying occurs as quickly as possible:

  • Take full advantage of good drying conditions. Begin cutting the crop early in the day (immediately before or soon after the dew is off) to fully utilize days known to provide good drying conditions. By waiting to the end of the day to cut, the drying time is pushed back by a full day or more. This exposes the curing hay to more risk of weather damage.
  • Use a conditioner on the mowing implement. A conditioning mower will aid crop drying greatly. Studies have shown the drying rate of a hay crop is 15 to 25 percent better when a conditioner is used. Two basic types of conditioners are available: an impeller (also known as a flail) and a roller-crimper.
  • Use the right conditioner for the crop being harvested. Impeller conditioners generally are better for fine-stemmed grass hay crops (for example, Bermuda grass and tall fescue), while roller-crimper conditioners are better for thick-stemmed species (for example, pearl millet and sorghum-sudan grass hybrids) and legumes (for example, alfalfa). Avoid using an impeller conditioner on alfalfa or expect another 7 percent leaf loss during the harvesting process. Leaf loss using the roller-crimper conditioner is minimal.
  • Spread the harvested swath widely. The hay producer’s best friend is sunshine. When the drying plant material intercepts sunlight, the energy of the light heats the plant and speeds drying. Therefore, using every square inch of the field to intercept the sunlight is important. For alfalfa and other legumes, however, wheel traffic over the top of the swath may increase leaf losses. In this case, laying the forage in a narrow swath at first and then using a tedder to spread the forage out may be best.
  • Use a tedder wisely. A hay tedder inverts, stirs and spreads out the hay crop. The proper use of a hay tedder can increase the drying rate of a hay crop substantially (15 to 30 percent). Further, the device is a relatively economical tool for the hay producer. Using a hay tedder on the morning after the crop was cut usually is best. Running the tedder after the dew has completely dried or when the forage is too dry can lead to excessive leaf shatter and losses. Try to complete all tedding operations before late morning.

Those who harvest forage crops need to follow the weather predictions closely, especially when the weather shifts to a “chance of showers” pattern. The end product of rained-on hay will lose desirable plant carbohydrates and the remaining forage dry matter will consist of less digestible cell walls, hemicellulose and lignin, resulting in higher acid and neutral detergent fiber with limited nutrient value and reduced value at the hay auction.

How riskily you manage your hay harvest depends on many factors and how well you trust your local forecaster. “I know I will not be forecasting weather anytime soon,” says Schroeder.

Source: North Dakota State University