A unifying concept for the dependence of whole-crop N:P ratio on biomass: Theory and experiment

Abstract

• Background and Aims: Numerous estimates have been made of the concentrations of N and P required for good growth of crop species but they have not been defined by any unifying model. The aim of the present study was to develop such a model for the dependence of the N:P ratio on crop mass, to test its validity and to use it to identify elements of similarity between different crop species and wild plants. • Methods: A model was derived between plant N:P ratio (Rw) and its dry biomass per unit area (W) during growth with near optimum nutrition by considering that plants consist of growth-related tissue and storage-related tissue with N:P ratios Rg and R s, respectively. Testing and calibration against experimental data on different crop species led to a simple equation between Rw and W which was tested against independent experimental data. • Key Results: The validity of the model and equation was supported by 365 measurements of R w in 38 field experiments on crops. Rg and Rs remained approximately constant throughout growth, with average values of 11.8 and 5.8 by mass. The model also approximately predicted the relationships between leaf N and P concentrations in 124 advisory estimates on immature tissues and in 385 wild species from published global surveys. • Conclusions: The N:P ratio of the biomass of very different crops, during growth with near optimum levels of nutrients, is defined entirely in terms of crop biomass, an average N:P ratio of the storage/structure-related tissue of the crop and an average N:P ratio of the growth-related tissue. The latter is similar to that found in leaves of many wild plant species, and even micro-organisms and terrestrial and freshwater autotrophs. © The Author 2008. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.