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Whiskey, Tango, Foxtrot | I worked for a hay/soil/tissue test lab for a couple years. I was a field man primarily but was around the lab enough to know what happened with the samples I brought in. I could go on for days about some of the ways a sample can vary (or be varied on purpose) so I'll try and keep er short.
Sample Size-The lab is going to test a very small portion of what you bring in (generally only several grams). If you pull 30 samples with some of these big old honkin hay corers, 95% of it is going to get dumped before anything happens. How the lab splits (dumps) the sample can vary the test A BUNCH. So a huge sample (5 gallon bucket size) isn't really necessary and is probably detrimental. What you want is not a big sample, but a representative sample. A zip lock bag (quart size) is plenty, whether you get it from 2 cores or 30. We used the wet chemisty method, which is more accurate, but much more expensive and time consuming. I am not up on how much a sample can change in the lab, but labs generally will vary quite a bit from lab to lab on the same sample. One of the reasons a lab didn't fly around here was the dairymen wanted the sample tested at the lab they trusted. A test from a lab here may be give the grower an idea of what the hay was worth, but they still based the price upon what their lab said.
Sampling-How the stack is sampled is very important to the accuracy. Ever seen a dairyman/broker walk around randomly probing bales, up, down, at a 45* angle, on the edge of bales, on the top, etc, etc??? They have no idea what in the hell they are doing. For square bales anyway (I've never seen a round bale up close, so I have no idea how to sample them) the probe should be made in the center of the face of the bale. Regardless of the size of the bale, it needs to be in the middle. When things are getting baled a little dry, all the leaves that are shattered by the plunger face fall will fall to the bottom portion of the bale on each stroke. Therefore the bottom of the bale (which may be turned by the balewagon/loader/squeeze later on) will as a general rule tests better than the top. 2 or 3 tie conventional bales can also be influenced by the way the hay is fed into the chamber. Dry hay on one side of a windrow from the sun coming up can make one side test better, etc,,, you get the idea. The middle is the best chance at getting a good sample.
For many of the same reasons you always want to sample all the way around a stack, not just one end. If the stack is say 50 units long, sample every other one, which gives you 25 cores. We always shot for between 25-30. I also try and vary the bale I would sample within a balewagon stack, as often the headlands on a square field can end up in the same place in every stack.
Finally the coring device itself. Our lab always liked the golf club probes. The reason is you can push it into the middle of a bale (on a good tight three tie bale it can take a lot of effort) and it will cut a perfect core out, and 25-30 of those should be a good representative sample of the stack, yet still be small enough in volume to be manageable for the lab. I always looked at the sample when you dumped it out of the probe, and it was a bunch of little circles of stem and leaf. That way I knew that I had taken a clean core of the bale. The biggest complaint with anything that is powered is that it invariably drags more stem or leaf (depending on the type of hay/moisture) into the sample. They also generally take a larger sample. The tip on a golf club style probe should be basically flat, a slight angle can make it cut easier and it should still make a nice core. I take a golf club shaft, whack it off where it is about 7/16-1/2” on the small end, and cut the other end off so it is about 20” long (the depth of a good core should be 18-20”) Braze the big end into a ½-3/4” pipe nipple. You can now thread this into a reducer that goes to a foot long section of 3” PVC pipe, with a threaded cap on the other end. Get a rod to tamp the sample out of the golf club after you pull a core or two and it will be in the pipe ready to dump into the plastic bag when you are done. Should be easy to whip one up in the shop, and IMO will take as good of a sample as anything you can buy. Since I can't describe in words very well what I am talking about, I would be more than happy to get a picture of a probe (assuming they haven't all been borrowed away) if you would like.
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Hay testing probes
