This review examines the potential far using soil solution as a tool for ma
naging soil fertility. A review of the current use of other types of soil a
nalyses indicates that, while their use in some cases is justified, there a
re substantial limitations to the development of reliable and widely applic
able calibrations. Factors that govern concentrations of nutrients in soil
solution and the methods for measuring them are reviewed in relation to the
ir use in nutrient management of forest plantations and agricultural crops.
Topics include a discussion of (i) nutrient supply and uptake mechanisms;
(ii) solution culture studies which define critical concentrations in solut
ion; (iii) methods of sampling solution from soils and (iv) estimation of c
oncentrations that can be maintained at root surfaces in soil. By inference
, nutrient supply would not limit plant growth if concentrations at most ro
ot surfaces (e.g, young roots in surface soil) were maintained at or above
concentrations needed to maintain high rates of growth in solution culture,
i.e. critical concentrations. Several aspects of this method have been val
idated for N and P in Eucalyptus nitens plantations. For example, when conc
entrations of ammonium (the preferred N source for E. nitens) in the field
fell below the critical level of 50 muM, plantations of E. nitens responded
to applications of N-fertilizer. This method was also useful for predictin
g P deficiency in corn (Zea mays), Eucalyptus globulus and E. nitens grown
in soils of widely different P-supply characteristics. The convergence of c
oncepts based on the principles of soil nutrient supply and uptake, which l
ink soil and solution culture studies, is likely to provide a unifying appr
oach for diagnosing nutrient-supply limitations to plant growth and a pract
ical tool for nutrient management in forest plantations. (C) 2000 Elsevier
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