by Ev Thomas and Bill Mahanna
Thomas is retired from the William H. Miner Agricultural Research Institute and president of Oak Point Agronomics Ltd.; Mahanna is with DuPont Pioneer and an adjunct professor at Iowa State University.
Wide windrows are routinely recommended for hay silage, but a drive through farm country during forage harvest season still finds many narrow windrows. Narrow windrows represent "Goldilocks management" with the top of the windrow getting too dry, the bottom remaining too wet and only the middle getting "just right."
Not only do narrow windrows take longer to dry to the desired level, but by then the leaves at the top of a narrow windrow of alfalfa or alfalfa-grass may be so dry that they shatter during chopping. When this forage is chopped, the "cloud of dust" coming from the harvester spout often isn't dust but pulverized alfalfa leaflets. Spreading the swath results in more uniform drying while exposing a greater percentage of the mowed forage to sunlight.
The conditioner on mower-conditioners may prevent making swaths that are more than about 75 percent of mowed width. Sometimes this will be good enough, especially with second and later harvests; if it's not enough, then a careful tedding can boost the speed and uniformity of moisture loss. However, using a tedder on recently mowed hay crops, especially on a heavy first crop, requires the use of good judgment. Similar to 007 agent James Bond's martinis - "Stirred, not shaken" - tedding should be done at a slow speed to prevent damaging the tedder.
Some farmers who don't bale any dry hay have bought mowers with no conditioner unit, encouraged by N.Y. research concluding that conditioning isn't needed if the crop will be harvested for silage. However, this only applies to silages that are 30 to 35 percent dry matter (DM); conditioning would still be recommended for silages harvested at higher dry matters, which most producers prefer in an effort to reduce protein degradation and clostridial silages.
Wide swaths are especially important when harvesting winter cereals including wheat, rye and triticale. These crops are typically harvested in May when drying conditions are less than ideal, and a heavy crop of lush cereal forage can be very hard to dry. A gentle tedding is often needed to get the crop dry enough to chop the same day it's mowed. Mow the crop in the morning, and if it's still slightly below 30 percent DM late that afternoon, lengthen the theoretical length of cut (TLC) to 1 inch and start chopping.
Research at the University of Delaware found that a winter cereal chopped at 26 percent DM right after it was mowed didn't contain any butyric acid, while 12 hours later butyric acid was 0.2 percent. That's because forage crops don't start to produce butyric acid until some hours after they're mowed. Similar results were found with alfalfa: No butyric acid at mowing, but a whopping 2.6 percent 12 hours later.
The use of disc mowers and mower-conditioners has resulted in more farmers asking this question: What mowing height will result in the best combination of yield, quality and stand longevity?
The answer depends on the forage species, plus some understanding of plant physiology. Alfalfa regrows from nutrients stored in its tap root, so mowing height has little impact on stand longevity with the exception of a fall harvest in the northern U.S., when a 5- to 6-inch stubble height is recommended to catch and hold snow. The cut stems of alfalfa soon die, so while a 2-inch versus a 4-inch stubble influences yield (and to a small extent forage quality), it has no impact on regrowth or stand life.
Grass is different in that it doesn't have a taproot, and the nutrients required for regrowth are stored in the bottom few inches of the above-ground portion of the plant. Mowing height of grass, therefore, has a considerable impact on regrowth and, in some cases, can influence stand longevity. The suggested mowing height for forage grasses and alfalfa-grass is about 4 inches - no less than 3 inches for alfalfa-grass.
Stubble height may be especially important during grass establishment: In a greenhouse trial at Miner Institute (Chazy, N.Y.), reed canarygrass was completely killed when it was harvested at a 2-inch stubble height, while that harvested at 4 inches regrew quickly with no apparent problems. In the same trial, orchardgrass cut at 2 inches wasn't killed but took much longer to regrow than when it was cut at a 4-inch stubble height.
Therefore, leaving a short stubble during the first cut of an alfalfa-grass seeding may do a good job of killing annual weeds, but it may also damage or even kill the forage grass.