The usefulness of Mehlich 3 (M3) reagent was evaluated as a method to extra
ct numerous elements from coalmine soils in As Pontes (Spain) showing a wid
e range of physiochemical properties. Critical levels (deficiency and/or to
xicity) were established for plant available elements extracted by this rea
gent. The M3 method was compared to 1M NH,CI, Olsen, acid oxalate, and DTPA
methods as extractants for exchangeable Ca, Mg and K, available P, non-cry
stalline aluminium, and available heavy metals, respectively. The M3 method
correlated significantly to NH,Cl for Ca, Mg and K (r = 0.76, 0.84 and 0.8
7, respectively), to Olsen P (r = 0.77) and to oxalate Al (r = 0.77). Signi
ficant correlations were found between Fe, Cu, Zn and Cd extracted by M3 an
d DTPA; for Mn, Ni, Co and Pb different relationship between methods were o
btained for acid and alkaline samples, so that critical levels were establi
shed for M3 metals as a function of soil pH. Copyright (C) 1999 John Wiley
& Sons, Ltd.