# Relative Humidity a Universal Truth for Hay Harvesting



## hay wilson in TX (Jan 28, 2009)

Here is one universal truth for hay.

Relative Humidity 
90% RH the hay will have no lower than 40% Moisture. 
The magic moisture for raking. 
70% RH the hay will be no lower than 18 to 20% Moisture 
The magic moisture for small square baling.
65% RH the hay will be no lower than 16 to 18% Moisture. 
The magic moisture for large bales. 
55% RH the hay in the 12% moisture

range where leaf shattering becomes a major concern.

The humidity we are talking about is down close to the hay, not free air humidity, not on TV and not at the Airport.

The devil is in the details and there are a number of details.

American Forage & Grassland Council, Association for Women in Science.

This is not original with me but it is something in my notes that applies


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## Nitram (Apr 2, 2011)

As I've never large square baled is the desired moisture content the same as in big rounds? 20 - 25%.


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## hay wilson in TX (Jan 28, 2009)

Small square bales will keep reasonably well if baled at 18% to 20% moisture.

Round bales and 3 X 3 X 8 squares do better baled at no Higher than 16% to 18% moisture.

The one ton Square Bales store better if baled at 14% to 16% moisture. 
Which is one reason it is popular to bale large bales with a preservative.

All that is conditional. These moistures were developed by researchers testing as they went along using an oven system to drive the moisture form the sample. They compute the moisture level measuring the difference in weight. 
*BUT* ! You can have hay that is fully cured with a stem moisture at 10% and surface dew moisture at 30% average 20% moisture and the hay will sweat a little but not mold. 
ON THE OTHER HAND in the late afternoon you can have hay where the leaves are 10% moisture and the stems (still) have 30% moisture. 
The result is 20% average moisture but all the leaves will shatter and be lost. You will have a bale of stems at 30% moisture. 
This will heat, sweat, mold, maybe catch on fire. At best you will have bale of moldy stems. 

Baling hay is a lot of art and some science. A very long time ago I baled hay by touch, feel, and exaggerated expectations. Put up some good hay but also put up some real horror stories.

Now I attempt to use only the science.

When I retire at 85, or older, I may go back to College to get a masters degree, with a paper on the exact moisture and humidity values that are involved. Even then it will only be valid for the local climate.

I fully expect to be thrown out of the program as a disruptive influence at, at least, two Cow Colleges.


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## HALLSHAY (Nov 30, 2008)

I am sitting in the field right now waiting for the RH to come up, but the breeze is keeping it at 40. We will start as soon as we hit 50% in the air. This should be about 13% moisture which is a little dry, but we have 120 acres of 2.5 ton perfect O&A and I want it in the barn by tomorrow afternoon!!!


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## Nitram (Apr 2, 2011)

Hay Wilson, thank you for the info I've been using the "hand method as learned from dad and had good luck so far. Last winter I purchased a Delhome portable tester. As I have been putting up prairie hay for my own cows and horses but hope to put up alfalfa again so moisture content is going to be more important to me.I thank you for all the valuable info you share with us


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## Grateful11 (Apr 5, 2009)

hay wilson is this from experience or a chart somewhere because that's nice info to have a around, thanks. It's 93 and 48% humidity 3ft into the air here right now but nothing to mow and if we don't get rain soon there's not going to be anything else for my wife to mow this year.


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## panhandle9400 (Jan 17, 2010)

We carry portable hygrometers in our pickups when it gets just right we know pretty easy , the hard part here is dont get enough humidity sometimes. hopefully got that issue lined out going to get a dew machine.we dont get to bale much during daylight hours that will be nice change. be able to see those pesky rattlesnakes. lol thanks wilson


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## hay wilson in TX (Jan 28, 2009)

Most of what I have come up with is thanks to others especially those University Studies. A very little is from observations and accepting the obvious.

This is from WV and it has some really good information. 
http://www.wvu.edu/~agexten/pubnwsltr/TRIM/5811.pdf
What I did was to enlarge the charts and graphs and picked values off them.

This is from Wisconson and I really took to heart the graph on page one, It is telling me that a really wide swath the hay will cure enough in 5 hours to stop plant resperation.

Somewhere else they mention that a full width swath will sit up on the stubble but hay dropped into a windrow will settle and rest on the dirt.

For the extra wide swath there is this vidio, 
New Holland Discbine Wide Thins - YouTube

It may sound strange to the grower in the humid east but growers west of me need some help if the night dew is not working. 
This machine is to pur enough moisture in a windrow to bale and not shatter leaves. 
Harvest Tec

This is a different system; Home

2011 is the first season that I would at times not have been able to bale hay, day OR NIGHT. In March thru June things were reasonably normal but August and September the humidity seldom got above 50% day or night. This was of academic interest only as with out irrigation there was nothing to bale. In July there were days that the humidity would go from 70% to 50% in less than a hour. The night humidity was in the 60% range about 5 am.

2012 will be better.


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