Can nutrient quality and sugar content of hay be improved by cutting in the afternoon rather than in the morning? This is sometimes suggested, but seems to contradict the idea of cutting in the morning to make haylage-in-a-day. There has been a great deal of conflicting information about AM/PM cutting in the farm media that has created some controversy.
The Case For Afternoon Cutting – Photosynthesis
During the day, forage plants convert sunlight into sugars by photosynthesis. Sugars and starch are produced faster than they can be translocated to root and crown reserves, so at the end of a sunny day, the plant sugar content is at its maximum. During the night, the plant continues translocating sugars from the leaves, and also uses up some of the sugars for respiration. As a result, the sugars contained in the harvestable forage will be at their minimum in the morning, before photosynthesis begins again. It therefore would seem reasonable that cutting late in the day would maximize the highly digestible non-structural carbohydrates (ie sugars and starches) and palatability of the hay. Some research has shown this to be the case.
The Case Against Afternoon Cutting – Plant Respiration
When a forage plant is cut, it doesn’t know it’s dead yet. It still thinks it has a fighting chance. Initially, plants on the top of the swath receiving sunlight will even try to continue photosynthesis, until limited by lack of moisture. Respiration using up soluble sugars continues until the plant is sufficiently dry that plant metabolism slows and eventually stops. The longer the drying period, especially the initial phase down to about 60-65% moisture, the greater the respiration losses.
It really doesn’t matter to the cow what the sugars were at cutting. Forage quality is determined after harvest and storage at the feed bunk. Overnight respiration losses of sugars can be greater than what is gained by waiting to cut in the afternoon. Research in New York and Wisconsin has shown this to be the case. Confused?
Drying Conditions, Humidity & Night Time Temperatures
The conflicting research results appears to be related to climate and the weather during the drying time of the studies. Overnight respiration losses are greater with higher humidity and temperatures. The original research showing the benfits to afternoon cutting was conducted in the western US, including Idaho and Utah. These locations have ideal, fast drying conditions with low humidity and intense sunlight. Remember, this is the part of the world where they bale in the evening with some dew on to avoid excessive leaf loss. They also have cooler nights, which reduces respiration.
Ontario Hay Making Weather Can Be Challenging
Contrast this with Ontario and our neighbouring provinces and states, where we struggle with high humidity, warmer nights, and the ever present threat of rain. Our overnight respiration losses are potentially much greater. There is some research in the northeastern US and Quebec that shows some potential advantage to afternoon cutting. This is more likely with exceptionally good drying condition (sunny, low humidity, lower swath density, etc). For example, the typically faster drying conditions of a lighter second-cut with excellent July weather may improve the conditions where the added sugars more than offset the added respiration losses. However, in the real, on-farm world of Ontario haymaking, will this be consistent enough?
Cutting late in the day also adds another day to the necessary weather window of good drying without any rain. If you check our weather records, I doubt whether this is very often a good risk. Rain-damage, or advanced maturity from delayed cutting because the weatherman can’t promise us the extra day, can easily offset any intended advantage. I’m not sure that Ontario farmers very often have the luxury of delaying cutting in an effort to potentially improve sugar content. Also, many farmers cut in the morning to spread the workload, because baling usually takes place in the afternoon.
Morning Cut “Haylage In A Day”
There is considerable interest in improving haylage quality by cutting in the early morning with wide swaths to speed wilting and then chopping it later the same day. Cornell University research shows this approach significantly improves fermentation and digestible energy. Even though sugars are at their minimimum when cut in the morning, losses of these sugars to respiration are also minimized with rapid wilting and no overnight respiration losses. Similarily when making dry hay, laying it out in a wide swath does more than cutting in the afternoon to improve forage digestibile energy. (Refer to “Wide Swath Haylage” https://fieldcropnews.com/?p=7181)
In my opinion, the time of day to cut forage for dry hay, is when you’ve figured out you’ve got a good chance to get it made before the next rain. Unless you have excellent, extended drying conditions forecasted, this likely means cutting in the morning. For improved hay quality, dry it and make it as fast as you can. Use the tools – cut a wide swath, condition properly, and make strategic use of tedders, rotary rakes, windrow invertors and propionate hay preservatives.