Good forage makes money, but poor forage is money lost. Tom Kilcer, of Advanced Ag Systems in Kinderhook, NY, has spent years researching forage production, forage quality, and livestock performance. Here’s what he’s learned.
Contrary to common assumptions, forage does not dry by the same mechanisms from start to finish. They are, in fact, three distinct phases, and understanding how forage dries is key to achieving the quality of forage product you want.
The first phase is the natural evapotranspiration of moisture along the stem and out through the leaf pores (stomata) — a very rapid process. Legumes, such as alfalfa, have 10 times more stomata than grasses, which means that they will actually dry faster than grass during the first phase. Stomata are open in daylight and closed in the shade, and will stay open until the plant reaches 57% to 65% moisture (younger, more tender plants lose more moisture before the stomata close). This, of course, is the ideal moisture level for making silage.
Of equal importance is the fact that the plant continues to respire, in the sun or in the dark, until it reaches 60% to 65% moisture, at which point the cells are no longer active. This respiration process equals a loss of highly-digestible carbohydrates (sugars and starches). In warm and humid conditions (like the centre of a swath), this loss can equal 16% to 30% of the initial dry matter. Prolonged wilting can reduce starch levels in red clover and alfalfa by about 56% and can result in sugar levels too low to ferment properly.
Once the stomata close, the plant continues to lose moisture through its skin, but at a rate 10 times slower, down to about 45% moisture. In the final phase, field curing removes the tightly-held water and dries the plant to levels suitable for dry hay.
The challenge, therefore, is how to minimize losses through respiration by rapidly drying the forage naturally through the plant’s stomata. Here are the rules:
Go Wide: Keeping in mind that the stomata close in the dark but respiration keeps going, it is logical to expose as much forage as possible to the light. Forage in a wide swath will receive three times more sunlight than a narrow swath, and this sunlight will also raise the temperature of the swath through the day.
Narrow swaths are much denser than wide swaths, reducing drying even more, and they hold heat and moisture inside the swath, increasing the rate of respiration. Research shows that only the top three-quarters of an inch of forage dries at a time: in a 3.5-foot wide swath, only about 22% of the forage is drying; in a 11-foot swath, 70% of the swath is drying at once.
The added bonus of wide-swath forage is photosynthesis: plants exposed to sunlight will continue to make carbohydrates through photosynthesis until they dry below 70% moisture. This process can actually more than offset losses from respiration: wide-swath forage can increase in potential milk production from the time it is cut until it is dry enough for silage. The process of photosynthesis also requires water, leading to more moisture loss from the plant.
Simply put, the wider the swath, the faster the drying. Kilcer has had the best experimental results using a sidebar sickle mower, which leaves the swath at 94% of the cutting width (though he hastens to add that he’s not advocating a return to this technology!). The most benefit comes with a swath that is at least 85% of the cutting width. If your mower is not capable of this, tedding the swath after 1 hour will be beneficial.
No Conditioning: Conditioning crushes the stems of the plant, breaking the capillary flow of moisture up the stems and out through the leaf stomata. This slows the initial drying process, and at the same time, it also increases the rate of respiration – a double whammy for forage quality. The research shows that conditioning in not needed for silage as it only increases the drying rate in the second phase of drying, from about 60% moisture down to around 40%.
Be Ready: Kilcer notes that at first, many farmers are not prepared for how quickly wide-swath, unconditioned forage will be ready to make haylage. First cut grass and alfalfa can reach less than 68% moisture in as little as one or two hours.
Kilcer’s research has shown that a 9 am cutting time results in the most efficient drying. Trying to get higher sugar levels in the forage by cutting late in the day will only work if the nights are cool and dry; otherwise the plants will continue to respire and lose carbohydrates all night long. Narrow swaths compound this problem by holding more heat and humidity overnight.
Harvesting forage the same day it is cut also increases overall yields by eliminating traffic on regrowth: studies have shown a 25% yield reduction on areas traveled 5 days after cutting; driving on the swath, on the other hand, doesn’t hurt it.
But what about dry hay?
According to Kilcer, conditioning forage is only required when making dry hay, and this is still best performed as a second step, once the plant has had a chance to dry rapidly through the first phase. Doing this 4 hours after cutting will result in dry hay after 3 days when using an accelerator and after 2 days when using a macerator (the accelerator crushes the stem while the macerator actually peels the waxy layer off the stems). Wide, loose swaths are still the best for making dry hay.
Making top quality forage is both an art and a science. An understanding of how hay dries and the impact of the drying processes on forage quality can help guide decisions on how to deliver the best quality forage to your cows. Good luck this haying season!
Gaining Ground is a multi-part series on cultural management practices for all management systems with a heavy emphasis on the importance of soil health and productivity. For the entire list of articles, click here.
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