Importance of Rapid Drying Immediately After Cutting
One of the often overlooked sources of dry matter and forage quality loss is respiration after mowing. Respiration is the breaking down of starch and sugars to produce energy (heat) and carbon dioxide. The process occurs in growing plants and continues after mowing, even in baleage and silage when heat is produced.
Data suggest that 2 to 8% of the dry matter may by lost due to respiration. Table 1 shows that, at current hay prices in the Midwest, a 4% dry matter loss results in $6.90 loss per ton of hay. Losses are greatest in the West where forage is often cut with a large cutter bar and put into a windrow that fits between the swather tires. This hay often takes 5 to 7 days to dry for baling, while some farmers of the same region put forage into a wide swath and bale it in two days. Not only does the faster drying time result in less dry matter loss but getting the hay off the field faster results in less wheel traffic damage to regrowth and higher yield of next cutting.
Respiration also causes a significant forage quality loss since lost starch and sugar were 100% digestible. As table 1 shows, loss of sugar/starch increases the content of remaining components. A 4% starch sugar loss would increase NDF slightly over 3%. Note that this is a drop of almost 20 points of RFQ. Thus if one had cut alfalfa at just below 40% NDF and lost 4% sugar/starch, the harvested quality would be above 40% NDF which is currently selling for about $50/t less!
What can be done to minimize losses from respiration? The first and largest good practice is to spread forage into a wide swath so that more sunlight is intercepted and stomates (breathing holes in the leaves) stay open to allow rapid drying of the leaves. Hay should be managed to dry to 60% moisture or less as quickly as possible, but at least the day it is cut. When forage moisture fall below 60% respiration is greatly reduced.
Hay that is put immediately into a windrow dries slowly inside the windrow and has high respiration rates for an extended time. Thus growers should spread cut hay into a wide swath (and drive over it) rather than to make a windrow that fits between the wheels.
Note that if a grower insists on putting forage immediately into a windrow and taking the respiration losses of sugar and starch, then the forage must be cut earlier to be below 40% NDF (150 RFQ) at baling or chopping if that is the goal. Cutting earlier to allow for the respiration losses means at least a 10% yield loss and greater stress on the stand thereby shortening its stand life.
A second method to reduce respiration losses is to make haylage in a pile or bunker or to make and wrap bales in plastic. Respiration requires oxygen. If packed tightly, the forage respiration will quickly use up the oxygen and respiration will stop. This practice is most effective reducing respiration losses if combined with forage put into a wide swath at cutting, dried quickly to 60 to 65% moisture and then ensiled or wrapped in a bale.
Forage is often 75 to 78% moisture when cut so the key to high yield of high quality forage is to manage so the first 15% moisture is lost as rapidly as possible. Reducing the unseen losses of respiration will increase yield and forage quality. Additionally, getting hay off the field faster will increase the yield of the next cutting.
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