pasture low in phosphorus?

have a pasture that tested really low in phosphorus.
How best to improve the ground. Top dress or should it be worked in? Maybe spread turkey manure?

Phosphorus is slow to leach into soil, especially clay soils. To do the best job, it needs to find it's way into root zone. Surface applied P will generally result is stratification.....Your Phosphorus/dollars remaining on surface layer. ie...best/fastest results if you work it in the soil to some degree.

the ground is mostly clay. How deep to work the ground? disk, chisel or maybe even rotovate?

We have no-tilled for 35 yrs. Corn made over 200 last yr. If is stratified doubt makes any difference.

nothing I know will make it work this yr. really needs to be applied 8months ahead of need. In my area, spreading with a dry spreader is the most economical way to make it work. all my studies show we have an over abundance of phosphate and lime sitting at the 4ft level. I wouldn't want it worked into the ground to get it well on its way to leaching out of the root zone.
might wanna buy some 'rapeseed' to mix in the dry spreader.

Same here for the most part, We've been 100% no til since the late '70's until a recent bit of experimentation. But as one of those experiments this past year we used a strip till unit on half of an 80 acre field we've farmed since the '50's. Put P and K down 8" to 10". Had best yields ever this past fall (due to many conditions, mostly great weather) . Parts of the field where we did NOT use strip till averaged just over 210. Areas where we DID put the fertility down deep went almost 240. Even with that, I'd want to see more data over a wider array of condition before I'd say the strip tilling was the only force at play here.

Also worth considering, a field that you've surface applied fertility for 35 years or more, you'll have SOME leaching and have SOME fertility work it's way down, even without tillage of any sort. A "new field" that hasn't had much attention, and may or may NOT be soil conducive to fertility movement in the first place probably won't have much P show up below surface. Lot of variables...

Bottom line, a new field that is P deficient going in would see FAR better results by placing P in root zone. (along with looking at conditions where P is tied up in clay soils. Just because you put it there doesn't mean it will always be available to the crop)