Testing for Plant Available Phosphorus in Soils

Keywords: Phosphorus (P) soil testing, fertiliser P demand, soil extraction, plant P availability, rhizosphere, Diffusive Gradients in Thin Films (DGT).

Phosphorus (P) has received a great deal of attention in recent years. This is due to a number of factors which mainly are: i) it is an essential plant nutrient, ii) it is limiting plant growth in large areas of the world, iii) natural resources are finite and iv) quality P reserves may cease in a foreseeable future. In this paper we will describe the basics of soil P and the main factors determining P availability to plants. We will theoretically describe the most common methods currently used in the agricultural advisory services, and present how these intend to measure plant P availability. Eventually, we will present and evaluate important studies that have tried to measure plant P availability using these methods. We conclude that any soil test is a drastic simplification of the complex processes determining P availability in soil. As a result, most of the classical soil tests fail to provide robust and reliable estimates of plant P availability when integrated across a range of different soils types. However, both theoretical and empirical evidence seem to suggest that the Diffusive Gradient in Thin Film (DGT) technique constitutes the most promising tool for the future of P soil testing to determine P fertiliser demands.

Simon Mundus, Andreas Carstensen and Søren Husted, University of Copenhagen, Faculty of Science, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.

24 pages, 4 figures, 78 references.