It was a popular topic of discussion this past winter at many forage meetings.  The research came from Cornell University and the concept was to mow and leave hay in swaths that were about 90 percent of the cutting width.  With such a system there was the obvious advantage of faster drying but also came a significant improvement in forage quality.  Here’s a closer look at the concept, the research, and the practicality. 

The Concept

        After forage is cut, two processes begin.  First, the crop starts to lose moisture.  As has been documented in many research trials and on many farms, the wider the swath is made, the faster the moisture loss.  More sunlight and air reaches a greater volume of hay in a wide swath and the plant is physiologically positioned to release moisture from leaf stomata (those little holes on the leaf surface that allow for air exchange).  A traditional narrow swath generally dries to hay baling moisture levels on top but often remains fresh and green on the bottom.  The mix of the two offers something in the neighborhood of haylage-harvesting moisture, but it takes longer to make it happen.  Conversely, a wide swath needs to be raked or merged to accommodate the forage harvester pickup head.  Leaf loss and the risk of dragging stones into the windrow become concerns. 

        In addition to moisture loss, forage quality begins to decline once the forage is cut.  This occurs from respiration, which breaks down digestible nutrients such as sugars (effectively the opposite effect of photosynthesis).  In average drying conditions, the amount of dry matter lost can be 5 percent.  However, it can be much higher under poor drying conditions.  Because most of these losses are highly digestible components, the impact on forage quality can be significant.  The only way to counter the losses is to dry hay more rapidly.  Hence, wide swath haymaking theoretically offers the potential to reduce respiration losses. 

Cornell Research

        In 2003, Tom Kilcer (Cornell University Extension) initiated a research project to evaluate the concept of wide swath haymaking.  It’s important to note that these studies were conducted such that the hay was swathed at about 90 percent of the width of cutting (e.g. a 9 ft. cutter laying an 8 ft. swath).  Swath core relative humidity remained significantly higher and temperatures significantly lower in the traditional narrow swath compared to the wide swath.  Both humidity and temperature impact drying time, which was also significantly different between the two swath types (Figure 1).  Note that the forage in the wide swath dropped from 80 percent moisture at cutting to 65 percent moisture in about 8 hours.  This essentially made it possible to cut and chop first crop alfalfa in the same day.  In a separate test, merging the wide swaths when they reached about 70 percent moisture (several hours after cutting) further reduced the drying time.

Figure 1.  Drying time for first-cut alfalfa with wide versus narrow swaths (Cornell)

        Perhaps just as impressive as the reduced drying time was the improvement in forage quality.  Both fresh and fermented forage showed the effects of the wide swath system (Table 1). 

        The fermented first cut alfalfa forage from the wide swath system also had a significantly higher ratio of lactic acid to acidic acid (3.1 vs. 1.5) and less ammonium-N as a percentage of total N (10.96 vs. 19.79). 

Practicality

        The early returns are impressive, but as always we must think about the barriers to making a wide swath system work.  First and foremost, most mower-conditioners (especially those wider than 9 ft.) do not allow for obtaining a 90 percent width swath.  Hence, we can assume that at something less than 90 percent we will obtain intermediate results.  Second, raking/merging must be done when forage moisture is around 70 percent. Finally, this system takes more management from the standpoint that you can’t commit to cutting more acreage than you can harvest before a) the forage gets too dry, or b) the weather turns nasty.  Regardless, the system (at the very least) should probably be viewed as a viable alternative for those many times when the haymaking window is something less than two days.  You can read more about the system and the results at: http://www.cce.cornell.edu/rensselaer/Agriculture/alfalfa_
research.htm