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Little River, TX | Obviously I fell in the same trap that I have admonished so many for doing. Assuming my Regional Truth is the Universal Truth.
I wish the charts that accompany the Manitoba information worked for me but all I see is a red X.
I would think the Truth that works here would have more universal application, seeing as they were documented in our Midwest.
If memory serves they in their finding that 75% of hay curing is due to the direct rays of the sun, they acknowledged that high humidity will discourage drying while a low humidity will facilitate drying. Their rational was that the advantageous temperatures and humidity are at least in part due to good sun shine.
When we consider the quality of sunshine the sun south of say Oklahoma City or Memphis the angle of the rays in mid winter are not much different than the angle on Manitoba or Alberta in mid summer. We just do not get the duration of sun shine you folks do. Here 14 hours from sunrise to sunset is about all we get, but at noon our shadow is up close to our feet. Here, in June, the sun will reach the bottom of a 25 foot deep hand dug well.
Now how this sun thing works. The day the hay is cut the stomatas are all open breathing in air and letting out water vapor and Oxygen. These little openings stay open as long as they see sunshine, as they close during the night. This is the route of escape for the leaf moisture. With alfalfa about half the plant is leaf so this is a considerable amount of the moisture. The stems can and do allow some moisture to escape through the leaves but the majority goes out through any openings in the stems. Cracked stems &/or the cut at the bottom of the stem.
Now what the sun does is it heats the moisture in the downed crop, creating a positive vapor pressure. This is why it is so important for as much direct sun shine to reach as much of the hay as possible, especially the first day.
Remove the sunshine and the stomatas close, be it night or a big windrow that cuts off the light. Then we fall back on needing a stem abrasion to give the moisture an avenue to escape. I suspect the reason why the massive crushing action conditioning system was developed in Canada is due to their/your less intense sunshine. It is also probably why the reconditioning system was also developed in Canada or one of our more northern states.
Someone, possibly in Wisconsin developed a chart to for the amount of total pan evaporation is required to cure hay down to 20% moisture. At least here we see a lot more pan evaporation when the sun is shining then when the sun is absent.
When the humidity at the windrow is at or above 90% the moisture level for fully cured hay will be above 40%. I contend the leaves will be 50 or 60% moisture and the fully cured stems will be 30 or 40% moisture for a aggregate moisture level in the 40% range. Then we can rake the hay with minimal leaf loss.
When the humidity inside the windrow is at or below 65% RH, the hay moisture will test in the 18 to 20% moisture range. When it is reasonably safe to bale, small square bales.
When the humidity in side the windrow is in the 50 to 55% RH range the hay will test about 12 maybe 14% moisture. About where it is supposed to be for large square bales.
Stem moisture (sap) complicates things, but as the humidity is falling here I can safely start baling in the morning as the humidity goes below 65%. When the humidity gets down in the low 50% range is when the leaves will start to shatter excessively. Here the measured humidity at eye level may be 50% with the hay still being damp with dew.
Baling at night, HERE, is not as complicated. We can feel the humidity and start baling. If the leaves are shattering too much we wait another 30 minutes and start again. We can bale until the baler's slip clutch starts complaining too much and/or the bales become too heavy.
So yes even with bright sun light, in Southern Lausanne, even though the temperatures go above 95°F, the humidity stays above 80% hay is slow to cure and impossible to bale.
Than again in Idaho with their highest humidity during the day not much above 20% and a nice 15 mph breeze they do not need sunshine, though they get it anyway. They simply do not NEED the drying effects of direct high angle sunshine.
I still go with the idea that hay curing is 75% due to sunshine. With our June sun being at 85° above the horizon which is considerably higher than the noon day sun in Regina, or Winnipeg. There the diluted sun shine forces the grower to fall back on the other elements that effect hay curing.
With air conditioned air blowing over plant samples I can cure the samples in the dark. I also can see the leaves will shatter while the stems are still limber with moisture,
If I were to attempt to put up hay in your country I would become totally confused.
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Can I cut alfalfa in am with dew on it?
