Predicting phosphorus limitations in Eucalyptus plantations

Phosphorus (P) fertilizers are currently used during the establishment phase of most eucalypt plantations. Phosphorus fertilizer is applied at a similar rate to nearly all sites, but eucalypts respond to P only at some sites. Site-specific management would improve the efficacy of P fertilizer use, so soil indicators of P fertilizer response in new eucalypt plantations warranted evaluation. Research focussed on soil solution, P, because that is the pool of P directly available to plant roots. Concentration of P in solution (both bulk soil and that predicted at the root surface) was related to rates of uptake and growth in solution-and soil-based studies. These and more commonly used indicators of soil P status were calibrated and compared in field experiments. In conclusion, an indicator of P intensity (CaC12 P was more highly correlated with response in different soil types than both quantity-based indicators (Bicarbonate, Bray no. 2, Acid extractable P), and predicted concentration of P at the root surface.