My advice; buy peat moss and organic lawn fertilizer. Compost all the materials you just mentioned. After the plants have sprouted and gotten established, you can use your organic materials to side-dress the plants to good effect.

JMHO.

In your zone, I think I would scratch it all right in the top of the soil..I wish I had some. The horse poop will help the cornstalks break down, and horse manure is the safest of manures to plants. Just scratch it in the top few inches of soil, keep it damp and airy, and watch it break right down. If you have lots of worms, they will work it over pretty fast. If you only have a few worms, they will reproduce like crazy in that environment. Just my thoughts. steve

I should add that all of this will be well mixed by a big tractor mounted tiller prior to planting, about 3 months from now.

Jim

I think you should be just fine doing it now.
Several neighbors and myself grow our gardens in pure horse manure. I've seen it scooped up from the corrals(fresh and aged) with a front end loader and put directly into raised beds. Seeds and plants were planted almost immediately. The sets looked startled a few days (they always do), but perked right up and did great. The seeds came up as usual and did fine.
When I first moved here I though the neighbors were crazy to do this, I had always heard that too-fresh manure would burn the plants, but after a couple of years of seeing their gardens do just fine and mine struggle, I became a believer.
Lots of old ranchers here garden this way. Horse poop is good, cow poop is better, sheep and rabbit is the best.
Good luck!

I vote yes, and I am almost sure I am correct because I have done it a number of times (precisely with horse manure and leaves). 3 months is a long time for manure, it cooks down fast. It will cook down faster when mixed with leaves, as the brown matter absorbs the excess salts (which are not that excessive to begin with, you will get it with a lot of bedding mixed in).

Further, there are a number of plants that will be unfazed by fresh manure, most notably cucurbitae (incl. melons), and in my experience tomato too. Brassicas and chard love 2-months old manure. Do not manure carrot, parsnip, and beans.

Jim, like steve said, horse manure is relatively safe, If it is mixed, SCRATCHE IN such that there are no big chunks of it anywher, then there shoul be no damege due to composting. I do not have the chemical analysis on it, also probably it is already mixed with other stuff and when you mixed it with soil it will be diluted more.
Also consider light mulching you plants with it when they are established and on top of that add some leaves as mulch.

But I would think that mixing in leaves(unbrokrn) now is too late, especially oak leaves. I do that in the fall so they rot and the worms work on them.

90-120 days before planting if fresh or 30 days if well composted and aged is the standard recommendation so if you aren't planting anything in it for 3 months you'll be fine. If it is really fresh I'd stockpile elsewhere for adding later but if its already well aged then I'd use it with no concerns.

As you know "burning plants" isn't the primary concern - pathogens are - so using fresh manure to grow vegetables in isn't recommended in any way.

Dave