DETERMINATION OF ASSIMILABLE PHOSPHORUS IN SOILS BY REVERSED FLOW-INJECTION ANALYSIS

A reversed flow injection system was used for the determination of assimilable phosphorus in 0.5 M NaHCO3 extract of soils. The extract sample diluted 1:10 was the carrier, and the reagents for the determination of the phosphorus were injected into the sample stream. The phosphorus was analyzed by using acidic molybdate by spectrophotometric detection at 660 nm. In this way no pretreatment was necessary to avoid CO2 bubbles. The calibration graph is linear up to 0.8 mg . L-1. The detection limit was 0.025 mg . L-1 for an injection volume of 119.5-mu-L. Sampling frequency was 70 h-1, and the precision was better than 1.72% for 11 successive assays. The accuracy of this method was evaluated by comparison with the results obtained by the reference method, and an excellent correlation was found (r = 0.9991).