Tero Laakkonen yo! a couple of monhs ago i posted here asking if anyone knew which deep-rooted plants i should grow to "mine" P & K in order to leave it for plants with not very deep roots?
Robert Kourik's _Designing and Maintaining Your Edible Landscape Naturally_describes "dynamic accumulators" as "plants that amass a greater than usual amount of a particular nutrient in their foliage," because they (a) accumulate an element in higher concentrations than other plants, even on soils deficient in that element? (b) thrive on soils with high concentrations of the element or (c) send their roots down to layers where the nutrients are in abundance. Your question relates to (c) which is harder to measure than the concentration of elements in the leaves.
Dynamic accumulators of phosphorus include legumes, buckwheat, and mustard (Brassica). Phosphorus is often in the soil in a form that is not available to plants; growing alfalfa in a field over a number of years steadily increases the amount of available phosphorus. Buckwheat and mustard solubilize phosphorus and subsequently excrete it from their roots. Other dynamic accumulators of phosphorus are bridal bower, calamus, caraway, chamomile, chickweed, dandelion, dock, garlic, lamb's quarters, lemon balm, licorice, marigold, meadow sweet, pigweed, purslane, sarsparilla (sassafras), skunk cabbage, sorrel, watercress and yarrow.
Potassium may also be present in a form that isn't usuable to plants, so liberating the potassium present in the topsoil may be as important as bringing it up from the subsoil. Green bracken ferns were used as a source of potash for washing in England. Other potassium accumulators include bridal bower, calamus, cattail, century plant, chamomile, chickweed, chicory, coltsfoot, comfrey, dandelion, dock, eyebright, lamb's quarters, mullein, stinging nettles, oak, parsley, peppermint, pigweed, plantain, sanicle, silverweed, sow thistle, creeping thistle, vetch, watercress, waywort, and yarrow.
Oak leaves have high levels of calcium even when there are low levels of calcium in the soil. I don't know what this means in terms of calcium "mining." Maybe the deep roots bring calcium up, or maybe the upper roots strip calcium from the surface soil. Kourik doesn't have any numbers. He refers to several books that might be more statistically oriented: Joseph Cocannour, _Weeds: Guardians of the Soil._ Ben Easey, _Practical Organic Gardening._ Stuart Hill, _Weeds as Indicators of Soil Conditions._ Ehrenfried Pfeiffer, _Weeds and What They Tell_
Have fun! --Rachel Findley email@example.com .