Selecting and applying metal oxides and clays for plant growth

A process of plant fertilization comprising:

• adsorbing a first amount of phosphorus from an anthropogenic phosphorus source onto a plurality of particles of at least one phosphorus adsorbent selected from the group consisting of activated alumina, activated iron oxide, activated bauxite, activated kaolin, and combinations thereof;
• then drying the plurality of particles of at least one phosphorus adsorbent;
• then, while the first amount of phosphorous remains adsorbed on the plurality of particles of the at least one phosphorus adsorbent, adsorbing an additional amount of phosphorus from the anthropogenic phosphorus source onto the plurality of particles of at least one phosphorus adsorbent;
• and
• then applying the plurality of particles of at least one phosphorus adsorbent to a plant medium,
• such that both the first amount of phosphorous and the additional amount of phosphorous are simultaneously present as adsorbed onto the plurality of particles of the at least one phosphorous adsorbent prior to the applying of the plurality of particles of the at least one phosphorus adsorbent to the plant medium.