Hydroponic culture

 APPLICATION   Hydroponic culture, where plants are grown in mineral solutions without soil, can be used to identify essential elements in plants.

 TECHNIQUE   Plant roots are bathed in aerated solutions of known mineral composition. A particular mineral, such as potassium, can be omitted to test whether it is essential.

 RESULTS   If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves.