This year’s hay making season is quickly approaching and already started for some producers. The time required to dry a crop from its initial moisture content down to about 15% moisture is determined by a number of factors, such as plant species, density of the crop, soil moisture, and the way the crop is handled. For any given situation, a combination of weather factors can cause the necessary drying time to vary from a day to over a week of rain-free weather. Studies of the weather factors that are related to the drying rate show the most important ones should be considered in this order:

Sunshine:

The sun provides the energy required to evaporate water from the plants. During June and July, when days are long, we have about 15 hours of sunlight between sunrise and sunset. In October, when the last cutting is made, the hours of sunlight are reduced to about 10.5. The lower angle of the sun during autumn also reduces the amount of available sunshine. When selecting a field to be used for hay, it is worth remembering that slopes facing south receive more of the sun’s energy, and there, drying should be faster.

Humidity:

The air that is moving across the top of the drying hay crop must be able to absorb the water which is evaporating, and mix it with the rest of the atmosphere. In this regard, air behaves much like a sponge or a mop. Sunny, warm days have the effect of lowering the relative humidity of the air and, thereby, increasing its ability to absorb water while also increasing the rate at which water is driven from the plants.

Wind Speed:

Since most drying takes place during the daylight hours, wind speed is an important factor during that time. Air next to the crop surface would soon become saturated under calm conditions and be unable to absorb additional water, so a certain amount of wind is necessary to replace it with drier air. Brisk winds and fluffy, porous windrows are distinct aids in increasing drying.

Dews:

Heavy dews may also delay drying time. Normally, heavy dews occur on clear nights when the earth, cooling, radiates its heat back to the sky. As the surface temperature drops to the dew point, water vapor in the air is deposited on the leaves and stems of the hay. At sunrise, the energy that would otherwise be used to dry the hay must be used to first evaporate the dew. Related to the moisture content of the soil, heavier dews usually occur for several days after a good soaking rain, then decrease in intensity as dryness continues.

Moist Soil:

A rain just before cutting may slow the drying rate by keeping the bottom part of the windrow moist even though skies are sunny and the humidity has lowered. Little can be done about this condition since cutting during fair weather right after a period of rain is an ideal strategy. However, an anticipation of slower drying and an additional turning or two may prevent this condition from becoming a serious factor. An early, heavy crop that is less porous in the windrow will take longer to dry since it is difficult for the air to move through it. Also, early heavy crops usually have higher initial moisture content and more water must be removed from them than from later, more mature cuttings which may have higher fiber content.

Haymaking Weather Tips

• Be weather wise. Listen closely to the extended weather outlook and the daily hay cutting advisory in addition to the forecast.
• Try to cut your hay just after a cold front passes in order to have the longest period of dry weather for the crop to cure.
• Use a hay conditioner, if one is available, to help speed up the drying rate and reduce the time the hay is left on the ground.
• Put the hay into a porous, fluffy windrow so the air can move through it easily.