Trends in modelling nitrate uptake

This paper puts the focus on two main approaches of plant nutrition. One deals with the overall interaction between nutrient supply and growth, which is referred to as "ultimate function modelling". The other splits nutrition in a number of "intimate functions", which are assembled together to mimic the whole plant behaviour. This view is illustrated by the challenge of modelling the uptake of a single element, N for instance. An amazing comparison of C and N acquisition by canopies deserves to be made. The so-called "law of N dilution" implies two properties: (i) plants can be compartmentalised into metabolic and structural pools; (ii) N accumulation in the biomass per unit of absorbed PAR is constant relatively to species and even to metabolic groups (C-3 or C-4) Such law may be introduced in crop models as a driving force when the supply from the soil is not limiting for growth. However, when nutrition is limiting, the existing models switch from this ultimate function to more intimate modelling which considers the interaction between the soil solution and the transport systems. Such abrupt switch highlights the lack of coherence between actual spatio temporal scales of approach and renders compulsory the intimate modelling of the successive steps between supply and plant demand.