Not all species require the same amount of each element. There are some unusual requirements, e.g., Si is required by Equisetum . Uptake depends on concentration. The rate of uptake of minerals is proportional to concentration, up to a point. BUT there also is active uptake.
Growth also is a function of mineral concentration.
Diffusion and mass flow in the soil is important when the level of minerals is low. When the level of minerals is high, uptake by the roots may be more limiting. In general, soil processes limit the uptake of minerals. The fungi secrete growth factors that stimulate roots to grow and branch. The earliest land plant fossils had mycorrhizae as many as 500 X 106 years ago.