I live in the desert with red clay soil known for being horrible. I have a vegetable garden and over the last year I have worked in amendment and garden mix that has helped with the soil structure making it looser and better draining. However, I tested my soil the other day and it is still completely void of N and K with P only fairing slightly better. Someone at the local nursery recommended working in a broad fertilizer that is 16-16-16 (half fast-acting, half slow-acting, at least the N). However, I was leaning towards a similar product that is 7-7-7 instead (the 16-16-16 fertilizer bag has way too much for my needs).

I am also planning on adding Mycorrhizae, Azomite, and an organic starter fertilizer (slow-acting 4-8-4) to each transplant hole.

My question is, do you think the addition of the recommended amount of the 7-7-7 fertilizer (along with what will be added to transplant holes) is enough to help get the nutrients where it need to be to start off the season or do you have other recommendations for me. Also, I should mention, I am planning on transplanting seedlings and direct sowing seeds within the next 5 days. Thanks for any advice you can offer!

I think that the 16-16-16 mathematically is the same as 8-8-8, you just use half the amount of the product. The slow half of the nitrogen that is slow release could take several forms, like a sulfur coating or larger granules or a different source of nitrogen. Often a cheap 8-8-8, 10-10-10, or 7-7-7 basic fertilizer will have no minors added..things like sulfur, calcium, magnesium, etc. More expensive fertilizers will often have those added,some now even have humic products and iron is also something often added to the mixture.
So what ever fertilizer you use in a chemical fertilizer check the label to see what you are getting, and compare prices too. I would definitely check with nurseries, co-ops, and neighbors to see what is normal in your area for nutrient needs and the best sources for buying them.
This may not be possible for you due to limited space, but if you have the space I would work on things like cover crops, adding all sorts or organic materials and even include some commercial chemical products into an area for a year or so before planting.
If you are going to be planting seeds I personally would not use any commercial fertilizer before planting, but would add a top layer of soil suitable for planting seeds ( something that would hold some moisture and not form a hard surface layer), then after they were sprouted and had some true leaves start adding diluted amounts of nutrients in the form of starter fertilizers, and build from that. Maybe you can even start to add things that would improve the soil along with the plant nutrients.
It is not so much the number 16-16-16, or 7-7-7 alone that is important, but the amount of product used.
I suppose the big disadvantage of testing the soil yourself it that unlike a professional soil test there are no recommendations accompanying the results. Maybe it might be a good idea, being you are just starting to garden in this location and have no passed experience to go on, to get a professional soil test with the recommendations on how to improve the soil. It might save you from making some mistakes early on that will take a long time to correct.

I'm new to gardening but have been reading "The Intelligent Gardener by Steve Solomon and it covers what you're talking about here. He has his own target levels that are designed for nutrient density, but the book breaks down exactly what to add based on a Logan's lab soil test. There's worksheets for different types of soil. "Acid-soil worksheet" "calcareous soil worksheet", etc. It's largely about balancing the nutrients in the soil. He only uses organic amendments though. Here's a really great website that has tons of info. https://soilandhealth.org/
Good luck with your garden.

I'd suggest reaching out to your county extension office.

They usually have a person on staff to help you with both amendments to your area specific as well as where to send for testing. They usually work with one of the universities in your state to offer a reasonable cost testing service and then you are usually given a report back via email that indicates where your soil is at, what is needed to be added, application amounts and how often this should be done and when to retest. It does help them if you will let them know what you are growing in the soil. If you need to borrow a probe to get your samples pulled, usually it's a deposit and returned to you at return of the probe.

The cost to do a basic soil test in my state I think was $17-21. You can add on specific things to test as well that may not be as common to your area (such as calcium, salts, magnesium etc). Usually you receive test results in 4-6 weeks depending on their work load. I did mine in fall and amended over the winter. I'll be retesting this fall to see where it's at. The nice thing about the state testing is they know what the soil is throughout and know how to remedy problem areas. Worth a look at their services in my book.

Hi OP. I agree with the others to have the soil tested. Knowing which trace elements to add or to avoid adding to your soil is very important. Too much of one thing is usually worse than having not enough of it in my opinion. Hope it helps.

The thread "Depleted soil" in Ask a Question forum

Get your soil tested by a professional lab and go from there. Don't just go throwing down fertillizers here and there. (Organic mulches are always good in the interim)

Nitrogen is often NOT tested because it fluctuates so much. In any case it's also easy to apply with ordinary/free products (grass clippings for example...)

Do any plants that you have growing SHOW deficienciesor stunted growth? If not, I wouldn't worry too much.

@LearnintoGrow

I fertilize PLANTS, not "the soil". Worms do that for me. If the plants are showing signs of deficiencies I address said deficiencies. For me last year, growing in containers, that meant weekly applications alternating magnesium in the form of epsom salts for everybody and leftover whey from my yogurt making to mostly tomatoes and occasionally peppers. Last year everything was in containers, growing in the mess of splinters and chunks of ground up lumber that passes for "garden soil" these days, I had to fertilize once a week with an NPK fertilizer, mostly for the N because wood chips tie up nitrogen when you have to plant IN it instead of just UNDER it (as mulch).

If you have caliche in your area I doubt you need to amend Calcium. I agree with others, get a soil test done by your local extension agency. There is hard caliche and soft caliche and they require different methods to deal with them, if you've got that.

Cover crops do wonders for breaking up and amending clay soils. Buckwheat worked well for that for me, but I'm not sure what kind of cover crops would be most helpful in your area of Utah. I liked buckwheat because once you plant it, you just mow it down (like with a regular mower) after it sets seed and it self seeds the next crop. Where I was living in OH, I could get 3 crops before winter set in. It doesn't have roots that go as deep as some clovers, but it generates a lot of root mass in the near layers of soil a lot faster, and a lot of vegetation up top, a lot faster than clover. It breaks up the clay a lot faster, or at least it has for me whenever I've used it. And its not hard to eradicate from your garden when its done its job.

Mulch heavily, use cover crops where you can, and worms will improve your soil for you. Last year I had almost no worms. Now I find them everywhere I stick a shovel into the soil or when I push the mulch back, they are there because I made a home for them and they are diligently doing the work of soil improvement for me.