Control of nutrient concentrations in plant growth media

Summary

Most nutrient-solution cultures used by plant breeders for screening varieties contain concentrations of P and trace metals far in excess of those found in normal soil solutions. Maintenance of realistic concentrations of these elements requires either that some concentration-buffering medium similar to that found in soil be used or that solutions be replaced before significant depletion occurs, usually by use of flowing cultures. A resin-controlled system for buffering solution pH and concentrations of phosphorus and any cationic nutrients is described. This system is capable of maintaining concentrations of the controlled nutrients within narrow ranges and is relatively inexpensive.

If the rate at which a nutrient diffuses to the plant root limits uptake in soil systems, solution culture may not be the appropriate screening medium. An equation describing the interacting factors that effect diffusion-controlled uptake is used to show which of these factors a particular screening process includes and which are absent. For nutrients that reversibly adsorb on soil surfaces, a modified sand culture system may simulate the soil better than solution culture. In such a system nutrients are adsorbed on particles of alumina (phosphorus) or on ion-exchange or chelating resins (most soluble cations or anions), and the particles are dispersed throughout a sand matrix. Limitations of these methods are discussed.