A Sand Culture System for Simulating Plant Responses to Phosphorus in Soil1

A sand medium containing activated alumina was developed to provide a range of stable, reproducible P concentrations in plant cultures. The lowest P levels compare favorably to concentrations found in soils. Activated alumina was “loaded” by absorption of phosphate from 0.01 m NaCl solutions containing KH 2 PO 4 . Phosphorus concentrations in solutions expressed from sand-alumina mixtures were dependent upon the P concentrations used to absorb P onto the alumina. Increasing the density of a specifically loaded alumina did not affect the average solution P concentration in the cultures but did result in substantial increases in total dry weight yields of tomato ( Lycopersicon esculentum Mill.) plants grown in the cultures. Thus, diffusion of P to root surfaces seems to be a prominent limiting factor in this system as in soils. The sand alumina culture technique shows promise for simulating plant responses to P at concentrations and under conditions comparable to those found in soils.