Composition of Dilute‐Acid‐Fluoride (Bray P1) Extracts of Illinois Soils

Abstract

The Bray PI reagent (0.03W NH 4 F + 0.02&V HC1) is widely used to extract "available P" from soils, but few studies have been made to determine the other elements that it removes with P. Illinois soils differing in pH and P fertilization were extracted with the PI reagent and also separately with its two components, 0.025^ HC1 and 0.03N NH 4 F. These extracts were analyzed for P, Al, Fe, Ca, Mg, Mn, and Si. Phosphorus extracted by the PI reagent or by 0.03/V NH 4 F was not correlated with soil pH or any of the other elements extracted. Combinations of Al with P in the soil, if they existed, could have been masked since the Al extracted by PI and by 0.03W NH 4 F were many times greater than the P extracted. Phosphorus removed by0.025/V HC1 was positively correlated with soil pH and with the Ca and Mg in the same extracts. From most soils the PI reagent removed more P than the sum removed separately by 0.03W NH 4 F and Q.025N HC1. However, the reverse was true for a soil naturally high in calcium. Removal of the "Al-P" fraction of Chang and Jackson markedly reduced the P removed in a subsequent extraction with the PI reagent. Also, very little Al was extracted by PI after the "Al-P" fraction had been removed.

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“…Extractable phosphorus can be broken down into two different forms, phosphorus 1 (‘weak Bray’) and phosphorus 2 (‘strong Bray’). The more commonly used measurement is phosphorus 1, which was developed to correlate with plant-available phosphorus fraction of the soil in slightly acidic soils ( Tandon et al . 1967 ).…”