USE OF THE FIELDES AND PERROTT SODIUM FLUORIDE TEST TO DISTINGUISH THE B HORIZONS OF PODZOLS IN THE FIELD

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Abstract
The Fields and Perrott test, originally devised as a test for allophane, has been shown to give a positive test with soil materials having reactive Al(OH)x. This includes the Bf horizon of Podzols. In the test, a drop of saturated NaF solution is added to approximately 10 mg of soil on a spot test plate. After 2 min, the pH of the suspension, as measured with narrow range pH paper, divided a variety of B horizons into two groups. The Bf horizons gave pH values above 10.3 whereas Bm, Bg or Bt horizons all yielded pH values below 10.2 with this field test. The C horizons of a number of Podzols yielded a variety of pH values but the values were all low in the Ae and high in the B horizons. This grouping was found to be a funtion of the content of oxalate-extractable Al. Ground gibbsite, amorphous Al(OH)3, allophane, synthetic dioctahedral chlorite and Bf horizons which had greater than 1% oxalate-extractable Al yielded pH values in 1 M NaF solution of 11.0 or higher. Therefore, the Fieldes and Perrott test cannot be considered as a specific test for allophane.