Hoard's Dairyman: Conditioning and wide swaths speed dry down

crops and forages

Conditioning and wide swaths speed dry down

by Kevin Shinners
The author is a biological systems engineering professor with the University of Wisconsin-Madison.

Rising grain and commodity prices make high-quality forages even more valuable to those feeding dairy cows. Efficient cutting equipment, rapid field drying, and a timely harvest with minimal loss and soil contamination are crucial factors in producing top-quality forage.

Forage plants have a remarkable capability to retain and regulate plant water; however, these mechanisms continue after cutting, preventing rapid drying. Harvesting practices like conditioning and wide swathing help overcome the natural barriers to water movement.

Laying the crop in a wide swath improves forage drying in several ways. First, it allows the drying crop to take advantage of the solar energy that strikes the field. A wide swath allows more of the sun’s energy to raise the plants’ temperature which then evaporates internal water. The sun’s energy also raises the water-holding capacity of surrounding air which allows internal water vapor to more readily leave the plant. Finally, wide, uniform swaths promote more air exchange around the plant, helping to reduce stagnant, humid air surrounding the cut forage. Placing the crop in a wide swath is the second most important factor we can control to promote forage drying.

The most important factor we can control is mechanically conditioning the forage stems. Mechanical conditioning helps water vapor leave the plant by overcoming resistance created by the cell wall, waxy cutin layer, and the closing stomata.

Immediately after cutting, the leaf stomata are usually open, promoting rapid water loss. However, research has shown that water vapor movement from the leaf stomata may drop dramatically within 15 to 30 minutes after cutting. Since it takes many hours to achieve the desired harvest moisture for haylage, water vapor that leaves the plant must then move outward through the cell wall and waxy cutin layer rather than through the stomata. This is why mechanically conditioning the crop is so important to achieving faster drying rates.

When the plant is crushed or crimped at many locations, and when the cutin layer is abraded or disrupted, the resistance to water movement from the plant is reduced. The choice between the right conditioner — roll or impeller — depends on the crop . . . alfalfa or grass.

Roll conditioners are the choice for alfalfa. They promote drying by crimping or crushing the stem. A crimping device passes the crop between intermeshing, noncontacting rolls which bend and crack the stem at intervals. A crushing device passes the crop through intermeshing rolls with small clearances, intermittently flattening the stem. In either case, plant moisture evaporates more easily from these breaks in the epidermis.

Impeller conditioners use rotating fingers to abrade the plant cuticle and to intermittently crack the stem. Comparisons between impeller and roll conditioners have shown that roll conditioners produce faster alfalfa drying, while impeller conditioners create slightly faster drying in grasses.

Over the last six decades, many researchers have explored the positive impact that conditioning has on a wide variety of forage plants. A careful review of this literature shows a consistently positive influence conditioning has on improved forage drying rate. When swath width and formation was similar, mechanical conditioning always resulted in faster drying compared to drying without mechanical conditioning. This is true whether the intended harvest is haylage or dry hay. Simply put, conditioning forage crops always results in shorter field drying time.

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