Comparison of Potassium Uptake by Four Plant Species Grown in Sand and in Flowing Solution Culture

Abstract

Plant species and cultivars differ widely in their response to the concentration of nutrients in the soil (Vose 1963; Epstein & Jefferies 1964). These differences, which have important implications in agronomy and ecology (Rorison 1969) may be the result of differences in both nutrient uptake and nutrient utilization. For plants grown in soil the rate of nutrient uptake is the result of interactions between the rate of absorption by roots, and soil processes that determine the rate of transfer of nutrients to the root surface. Transfer processes in the soil include (a) diffusion induced by a change in ion activity at the root surface; and (b) mass flow induced by transpiration. The rate of transfer of nutrients by diffusion and mass flow is dependent on the ionic species involved and on a number of soil characteristics, including water content (Olsen & Kemper 1968; Barley 1970). Differences between species in rates of nutrient uptake can only be observed independently of transfer processes when nutrients are maintained at near constant concentration close to the absorbing root surface. This requirement is approached in systems of plant culture where nutrient solution of constant concentration flows continuously through the entire root system (Asher, Ozanne & Longeragan 1965). Our objective was to compare, under similar environmental conditions, the response of four herbage species to a range of potassium concentrations in flowing nutrient solution, where transfer processes are relatively unimportant, and in sand culture, where transfer processes might be more important. There is evidence that two of the species used (Dactylis glomerata and Trifolium pratense) require a high supply of potassium, and the other two species (Anthoxanthum odoratun and Medicago lupulina) require only a low supply (Brenchley & Warington 1958; Kruijne & de Vries 1963). Three (Dactylis glomerata, Trifolium pratense and Medicago lupulina) are cultivated species, whilst Anthoxanthum odoratum occurs as a common component of permanent grasslands in western Europe.