How to obtain a proper soil sample?

[TheWaterbug]

For the last 3 years I've pretty much been winging it, but I'm thinking I should probably get my soil tested so that I put the right stuff into it.

My soil has some pretty discrete layers:



The top 4-6 inches are pretty decent topsoil, but the next 4-6 inches are heavily compacted sand, and below that is clay that goes on forever.

If I want my "soil" tested, do I want to test the top layer? The sand layer? A mix of the two? Or of the three?

When I use my broadfork:



I loosen pretty much the entire sand layer and bring up a few inches of clay, and then the rototiller mixes it together.

It's been suggested that I apply some gypsum to prevent it all from reforming into hardpan again.

I have no idea how much I should add, nor how to actually apply it.

[SOB]

I would think your county extension office should be able to help you with how to get a proper soil sample. I have attached a link to the OSU fact sheet for soil testing. It shows how to sample a lawn but the same procedure can be done for a garden I'm sure.

http://mahoning.osu.edu/topics/master-gardener-volunteer-program/plant-and-pest-diagnostic-clinic/Soil%20Test%20FS.pdf

As for gypsum, I don't think there's a right or wrong way of applying it. I would just sprinkle it on top of the soil and incorporate it into the ground when you till. I have read that it is beneficial for loosening the hard clay but it takes a while (and a lot of it) to see any results.

[cwayland]

Have you picked up the soil testing kit yet? They generally have very specific directions for how to sample. I believe they specify to take a certain number of core samples from various spots in the area you want tested. They will tell you the depth (I can't remember what it is). You then mix it up, bag it, and send it in.

[Tonio]

I couldn't find the LA county extension for soil tests, but here's the info for their helpline http://celosangeles.ucdavis.edu/Common_ ... Questions/

Not all UC Davis extensions offer soil tests.

[orgoveg]

I'm thinking that since you can only amend as deep as you can till or fork, you only need to sample that deep. I have instructions and sample bags for an Ohio soil testing lab. I don't think it specifies a depth, but it directs you to take many samples from the area and mix them together (after they dry out). Then, put a sample from the mixture in the bag.

[TheWaterbug]

I couldn't find the LA county extension for soil tests, but here's the info for their helpline http://celosangeles.ucdavis.edu/Common_ ... Questions/

Not all UC Davis extensions offer soil tests.

Thanks! I just sent them an email, but this article suggests that California has cut its soil testing services. I find this very odd, considering how important agriculture is in California!

Nevertheless, the article refers me to UMass Amherst, which offers soil testing to anyone for only $10, or $15 if you also want an organics report.

For $15 I think I'm going to try the UMass service, and if UC Davis comes back with anything reasonable, I'll try that, too.

Good to know about the sample methodology. orgoveg, that's a good point; no reason to sample any further than I can fix!

[SOB]

Good to know about the sample methodology. orgoveg, that's a good point; no reason to sample any further than I can fix!

Keep in mind that nutrients and roots go much deeper than what you can reach with a fork or tiller, etc.