EXCHANGEABLE PHOSPHORUS, ESTIMATES OF IT FROM AMORPHOUS IRON OXIDES, AND SOIL SOLUTION PHOSPHORUS, IN RELATION TO PHOSPHORUS TAKEN UP BY MAIZE

Abstract

Summary Amounts of phosphorus taken up by maize plants during 23 days from an Entisol, two Alfisols and an Ultisol from Nigeria, each with three histories of management, were related to the concentration of soil phosphorus extracted in 0.01 m CaCl 2 ; but the relationships differed between kinds of management. Phosphorus in plants 51 days old was not related to concentration. Relationships of plant phosphorus with isotopically exchangeable phosphorus, and with phosphorus extracted from the soils by anion exchange resin, were poor in young plants but were good in the older plants, irrespective of field management. Amounts of phosphorus in the older plants were also well related to estimates of exchangeable phosphorus computed from P in solution and amounts of amorphous iron oxides extracted by ammonium oxalate from the soils, using equations derived in an earlier investigation with a larger group of soils. Thus estimates of exchangeable phosphorus made from simple measurements of the soil constituents that largely control it, and from extraction by resins, are potentially useful to indicate the ability of soils to supply phosphate to crops, and hence to guide fertilizer policies.