Soil building plants for tough conditions

I have a large area of dry open meadow with very poor clay soil with very low organic matter content. There are plants growing there now, but they are only very hardy invasive species and even they struggle to make it to a foot tall. The dominant plants are sulfer cinquefoil, yellow starthistle, slender plantain and medusahead grass. The climate is a hot dry summer, cold wet winter climate with a little over 25 inches of annual precipitation including some winter snow. My question is what kinds of plants could I plant in bulk to speed up the soil building process.  Ideally I would be looking for plants that would put out a lot of biomass and add organic material fairly quickly and would be able to handle the climate and poor soil. I'm guessing annual and perennial forbs would work best but I would also be open to woody species that would be fast growers under these conditions. I know plants like comfrey are famous for improving the soil but would they be able to handle the poor conditions as well as compete with all the weeds if left on thier own? It is a pretty large area so ideally I'd like to just throw some seed and let it takeover.  Just looking for some ideas. I'm open to any input.

Corn, peas, blackberries.

Travis Campbell wrote: My question is what kinds of plants could I plant in bulk to speed up the soil building process.  Ideally I would be looking for plants that would put out a lot of biomass and add organic material fairly quickly and would be able to handle the climate and poor soil.

I recommend grasses. Grasses capture and utilize sunlight better than any other plant or tree. They can grow tons (literally) of biomass that can be used for mulch (hay) and also in a compost pile, nurturing and growing soil bacteria and fungi to be added back to your soil and used to make teas to add to the soil also. Their roots can grow deep, and just roots growing and dying adds organic matter to a soil without having to till or disturb the soil.

Like James, I'd recommend grasses but I'll add in grains and clovers into the primary mix.

To build soil quickly (1 to 2 years is quick) you have to still have diversity and you need that diversity to include nitrogen fixing plants, deep rooting plants and coarse leaf type plants.
So most grasses are going to be able to do this, but that also tends to reduce diversity since they a grass mix is still all mostly shallow (under 2 feet) rooting plants.
By adding in items like clovers (n fixers) and grains (heavy stalk material, deep roots (over 3 feet) the soil will, in a single growing season be able to be chopped and dropped two or three times, the root mass increases after every chop down allowing for the microbiome to diversify further into the soil.
The mulch left from the chop and drop covers the soil, holds moisture in, provides an ingress path way for new fungi spores and bacteria, and attracts worm which come and pull organic matter underground which is where you really want it to end up.

After the first year you can add things like rape, daikon, turnip, etc. which will all add deeper organic matter when the field is chopped and let lay a couple of times during the second growing season.

The third year (or at any point during the whole process) you can add mushroom slurries, coffee grounds, and any other organic items as long as they are microorganism attractors or earth worm attractors.
If ants come, they are good indicators that there is moisture in the soil and they do great at pulling organic materials into the soil, creating air ways (that also hold rain water) and they usually fertilize with their dead bodies as well.

Redhawk