Evaluation of sand‐alumina‐P media for studies of P nutrition1

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Abstract
Sand cultures in which P is supplied by a solid‐phase buffer offer several advantages in studies of P nutrition. Phosphorus concentrations may be maintained at realistically low levels, P supply can be localized in the medium, and roots can readily be removed from sand. However, information on pH, P adsorption and P desorption is needed to use solid‐phase buffers effectively to simulate P supply in soil. Experiments were conducted to characterize the effects of acid washing treatments and P concentration on P adsorption by alumina, and subsequent desorption of P from alumina‐P. Increasing the concentration of H in acid washing treatments decreased the equilibrium desorption P concentration and solution pH for any given adsorption P concentration. Increasing P concentration of adsorption solution led to increasing P concentration and pH of desorption solutions. Further experiments were conducted to determine the effect of percentage alumina‐P in sand‐alumina‐P mixtures on P concentration in the solution phase and on P accumulation by maize (Zea mays L.) seedlings. Solution phase P concentration was unaffected by percentage alumina P, but seedling growth and P accumulation increased in a linear manner with increasing percentage alumina‐P. Phosphorus supply in a sand‐alumina‐P mixture was compared to that in a soil‐sand mixture. Sand‐alumina‐P had higher Bray #1 P concentration than soil‐sand, but lower P concentration in an equilibrium solution. When P was added to sand‐alumina‐P or soil‐sand mixtures, P concentrations decreased more rapidly and there was less net increase in P in sand‐alumina‐P than in soil‐sand. Results confirm the utility of sand‐alumina‐P mixtures as a solid medium for studies of P nutrition, and provide the basis for establishing predetermined P concentration and pH in the medium.