Use of modelling to understand nutrient acquisition by plants

The definition, testing and uses of explanatory models in plant nutrition are discussed and contrasted with descriptive, predictive models. Two examples are given. First a model of phosphorus acquisition by rice plants growing in soils that undergo flooding and drainage, in which changes in the soil induced by roots are important. The changes are, in flooded anaerobic soil, oxidation of mobile reductants and consequent production of H+ ions in the soil as well as direct release of H+ ions from the roots to balance excess intake of cations over anions; and in non-flooded aerobic soil, release of organic anions from the roots. The model's predictions are tested against experimental data. Second a model of N acquisition by rice plants in flooded anaerobic soil, in which the uptake properties of the roots are important. The contribution to N uptake of NO3- formed in the rhizosphere of rice in flooded soil is compared with that of NH4+ from the bulk soil using a model and absorption properties of rice roots measured in nutrient culture. The models' uses and limitations are discussed.