Solution Ion Activity and Plant Growth

The relation of ion uptake to soil solution composition is discussed. Uptake of a given ion depends not only on its activity in solution, but also on the activity of other ions and the relation that exists between solution ions and exchangeable or solid‐phase ions. Methods of combining all these factors are reviewed and evaluated. A dimensionless plot, suggested by Howard and Adams, which related relative plant growth to the ratio of the ion activity to the sum of ion activities in solution, a i /Σ n 1 a i , seems to have a wide range of applicability that extends from uptake from a nutrient solution in a beaker to uptake from soil solution in situ .