The Hedley procedure will be applied on the mixed species plantation of acacia and eucalyptus to see if the tree growth between the end of the 1st rotation (7 years) and 2 years of the 2nd rotation has an effect on different P Hedley fractions, mainly the 4 first fractions i.e., Resin P,0.5 M NaHCO3-P, 0.1 M NaoH-P -P and M HCl.
Malachite green is much more sensitive than the Ascorbic acid in P analysis, and therefore can be used for P estimation where its concentration is expected to be very less in extract/aliquote.
The attached papers may help.
I never used malachite green in the Hedley procedure. I'm not sure, but I think this method is sensitive to other ions in solution, specially Silicon. If it is true, you may have problems of overestimation of P content because the stronger extractants used in some steps of Hedley procedure.
I played around with it some before i started my lab work, As best i recall i did not enjoy it. I had difficulty with repeat-ability. Ascorbic acid method much better to work with. However basic extractants dont play nice with these methods.
Also note (Tiessen and Moir, 1993). If you dont adequately filter organic acids, they will precipitate (some will) and futz up the colormetric reading.
Tiessen, H. and J.O. Moir. 1993. Characterization of available P by sequential extraction. In: Carter, M.R., (ed.). Soil sampling and methods of analysis. pp. 75-86. Canadian Society of Soil Science.
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