Soil solution and other soil analyses as indicators of nutrient supply: a review

Abstract

This review examines the potential for using soil solution as a tool for managing soil fertility. A review of the current use of other types of soil analyses indicates that, while their use in some cases is justified, there are substantial limitations to the development of reliable and widely applicable calibrations. Factors that govern concentrations of nutrients in soil solution and the methods for measuring them are reviewed in relation to their 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 solution; (iii) methods of sampling solution from soils and (iv) estimation of concentrations that can be maintained at root surfaces in soil. By inference, nutrient supply would not limit plant growth if concentrations at most root 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 validated for N and P in Eucalyptus nitens plantations. For example, when concentrations of ammonium (the preferred N source for E. nitens) in the field fell below the critical level of 50 μM, plantations of E. nitens responded to applications of N-fertilizer. This method was also useful for predicting P deficiency in corn ( Zea mays), Eucalyptus globulus and E. nitens grown in soils of widely different P-supply characteristics. The convergence of concepts based on the principles of soil nutrient supply and uptake, which link soil and solution culture studies, is likely to provide a unifying approach for diagnosing nutrient-supply limitations to plant growth and a practical tool for nutrient management in forest plantations.