Diluted Seawater or Sea Salt. Every element is present in the sea and by diluting it to the same salinity as your blood, they can be absorbed by plants to fill trace mineral requirements and improve soil quality through flocculation.
Gather top inch of seawater where it crashes on rocks. Dilute 1:30 for 0.1% salinity, or 1:10 for 0.3% salinity. Alternative: add 1g sea salt per liter for 0.1%, or 3g per liter for 0.3%.