Certainly you can plant. The lot will be way too high in P and K, so no NPK fertilizer for the next 15 years or so. N may have already dissipated, or it may still be high. You may get huge crops for leafy greens and poor crops for beans in the first year, if N is still high. You may also get forked carrots and parsnips, and lower tomato yields.These effects will dissipate over time, and in a couple of years you may even have to add nitrogen fertilizer only.

The only way to know whether the Phosphorus and Potash is too high, too low, or about right is to have a good reliable soil test done of the soil in that proposed garden plot. An in depth look at the soil will also help answer other questions that are just as important such as the soils pH, drainage, soil life, type of soil, and about as important as the rest how much organic matter is in that soil.
Contact your state universities Cooperative Extension Service office about having a good reliable soil test done and also dig in with these simple soil tests,
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to see what else you can about that soil.

Just for comparison: in my garden, 5 inches application of compost brought the P soil from very low (7ppm) to too high (100 ppm) two years after application. Manure is higher in P than mixed garden compost (leaves and wood chips). K went from 170 to 300 ppm (also too high), and manure is higher in K too. You can estimate the soil content, if it is clay (i.e. mineral retaining) if you know how many horses lived there.

Sounds great to me.
I have a section of my garden where manure was dumped a few years ago. I spread it around, but it was probably at least 6 inches deep in that area when I stopped spreading. I've gotten awesome crops in that area (better than the rest of the garden, which got 3 - 4 inches spread over it.) each year since.
Corn and squash did especially well. Beans did well, as did potatoes.

Thanks, glib -- now I know why my soil tests v high in P and K (when it started out low.)

Thanks for the advice!
I've tilled (just like butter!)... and planted about half my garden in the dry lot.
Tilled part of the pasture... so far ,,,way more work!
Shall see what happens this summer.

My pasture had about 4x the worms as the dry lot digging this spring.
5 or so vs 20.
I was running frogs and toads out of the dry lot with the mower last fall. The few worms I found this spring were much larger in the dry lot... all though smaller they were much more plentiful in pasture.