I use and buy fresh or dried kelp for my compost tea brews because it contains lots of potassium and above 40-60 micronutrients. I spray it as a foliar/soil drench over all my lawn and garden plants. I above 5 hours from the nearest beach.

What is a substitute for this on a sustainable farming system, that I can make or grow myself?

For the other minerals, try a mixture of comfrey, yarrow, dandelion, and nettle. Grow a special bed of them or just tuck them in waste space, harvest the leaves, macerate, and make tea. Marine plants concentrate the nutrients more, though, so you will need more of the land plants. The "weeds" all have deep root systems that collect minerals from subsoils, then the plants put them in the leaves where they can rot into the surface soil.

This might not replace kelp, but it could considerably reduce the amount you use.

What about deep rooting cover crops like rye or oats? Do these plant do the same thing, far as bring forgotten nutrients from the subsoil to the topsoil?

Maybe that is also another "kelp" replacement method...

Now I have another question: What do you do when you have exhausted most of the micronutrients that were in the deep subsoil, by years of growing and consuming up your crops and cover crops? How do you replenish those nutrients back into the soil system, without going outside your farm site and obtaining something like extra kelp products or maybe comfrey, stinging nettle weeds, etc. from a remote site, in order to build up your soil system?

However I was wondering if all the above alone, would supply all my crops those rare micronutrients that some crops need that is native in seaweed products.

You seem to be focusing on micronutrients as similar to vitamins when in fact there are just what they represent: elements needed in very minute quantities compared to NPK and even the secondary nutrients. Micronutrient deficiencies are common to some soil and in some seasons but mosly are readily available in a living soil supplied with adequate organic material.

If the trace and micronutrients come out, they have to go back from somewhere.

That said, many plants do well under less than perfect conditions.

Kelp Meal is a commodity. This means that shipping costs are often higher than the cost of the kelp meal, itself.

Katey

The link below is a great resource for not only composting, but soil health and vitality.

Now, to get the grasses - and I mean buckwheat, wheat, barley etc - to hyperaccumulate the minerals the best thing to grown them in is (drums please) diluted seawater.

See Maynard Murray's earthshattering work and those works that followed on from his.

Now, you can DIRECTLY use the seawater IF PROPERLY DILUTED. There are hydroponic charts that indicate the parts per million for commonly grown plants.

This might seem controversial to some but trust me I have done it. And achieved superior results to the sissified chemical fertilizers that cost $.

I grew a potted water melon in a sterile media with only diluted seawater (1400 ppm) with success. I have treated infested plants with seawater and the infestation went away in 10 days.

The minerals allow the plants to defend themselves. And sodium seems to enable the other 92 elements to be absorbed. Seaweed is a hyper concentration of ocean water. Ocean water is a hyper concentration of soil run off. This is a zero sum game!

So again, the plants, animal waste etc can't supply what isn't in the media that generated them. Chicken manure is rich in X is a farce if the chickens weren't eating a food rich in X.

In my country seaweed washes up in the winter and old school farmers collect it by the truck load. New school cats buy inferior products (3 - 15 elements at best) with inferior results.

Oddly enough, some even say that many chemicals fertilizers and pesticides are merely supplying the nutrients so the plant can generate its own defenses...in the same way as natural fertilizers but in a proprietary form so that you gotta pay lots of money!

The 2 post potent fertilizers are free for all. Carbon and nitrogen, both in the air.