By Dan Undersander
At on time, we cut hay and laid it in a wide swath for drying behind the cutter bar. When conditioners became commonplace, many growers came to think that a wide swath was no longer important when making dry hay or haylage. This is completely false — the two are independent, and both are needed for faster hay or haylage drying. A wide swath enhances leaf drying while conditioning expedites stem drying.
When we cut alfalfa or a grass, it is generally 72 to 77 percent moisture. This means the crop must lose about 3 tons of water per acre (up to 720 gallons) to dry to haylage at 60 to 65 percent moisture. For dried hay, the impact is even greater. It must lose 5.7 tons of water per acre (1,370 gallons) to dry to 13 percent moisture when the yield is 2 tons per acre dry matter!
Put the plant to work
A large portion of the initial water loss is from the leaves through the stoma. In an effort to the cool the living plant, the stomata open to exchange gas and moisture between the leaf and outside air. Stomata open in daylight and close in darkness. Keeping this in mind, know that more stomata will remain open in a wide swath while many more will close if put into a narrow windrow where it is dark.
As plants respire, they give off carbon dioxide, heat, and sugars. It continues after the plant is cut. Since the sugars are 100 percent digestible, we want to reduce their loss. Normally, sugar losses range from 2 to 6 percent.
However, losses can be higher when it takes longer to dry hay.
Respiration rate is highest at cutting and gradually declines until plant moisture content has fallen below 60 percent. Therefore, rapid initial drying to lose the first 15 to 20 percent moisture will reduce loss of starches and sugars and preserve more total digestible nutrients in the harvested forage.
The second route for moisture loss in forage drying is through the stem (Phase II drying). Stems on legumes generally have lower surface to volume ratio, fewer stomata, and are covered by a semi-impervious waxy layer. This layer needs to be cracked or scraped to promote water loss from the plant. Conditioning will enhance the speed of haylage drying in a wide swath from 0 to 4 hours. However, conditioning is imperative for haylage not put into a wide swath and for hay making. Conditioning is most effective if the conditioner is properly adjusted (about 5 percent leaf bruising).
Research at the University of Wisconsin Arlington and Marshfield Research Stations have demonstrated the value of making wide swaths in hay or haylage making. The figure is a representation of a typical drying curve for alfalfa either in a windrow (covering 30 percent of the cut area) or in a wide swath covering 70 percent of the cut area.
Notice that the wide swath was ready to be harvested for haylage the afternoon of the day it was cut but not ready for harvest until the next day if put immediately into a windrow. If the curves are followed out for drying hay, there was about a one day difference in drying time between a windrow and a wide swath. How often would this mean the difference between rained-on hay or not?
Better forage quality
As the table shows, we also averaged higher forage quality, due to lower respiration losses during drying. We saw a forage quality advantage to wide swaths about 70 percent of the time. Samples generally had higher NFC (and, therefore, lower NDF). This difference resulted in higher lactic acid content of fermented haylage.
If making a wide swath, one must drive one or both wheels on the cut hay. Research has shown that this causes less loss than making a swath narrow enough to fit between the wheels.
Awareness of the importance of a wide swath is crucial as many farmers are getting mower/conditioners with larger cutting bars. The hay is still conditioned through a conditioner of the same width as smaller units, so making a swath to cover 70 percent or more of the cut area can be more difficult. Use of fins on the back baffle or other devices to spread the hay into a wide swath may be justified.
Single most important factor
A wide swath is the single most important factor to rapid forage drying and preserving the harvested forage quality. This is true for alfalfa, grasses, and mixtures. Conditioning may enhance drying for haylage and is certainly required for hay making. Also, keep these key points in mind.
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