Modelling plant nutrition of horticultural crops: a review

In this review, studies in plant nutrition are-classified according to their time scales and micro-or macroscopic level of approach. Short-time scale studies are mostly dealt by plant physiologists with the prospect of building mechanistic models. They describe elementary plant functions implicated in, or dependent on ion uptake, with the goal of explaining the mechanisms underneath the functions. The concept of 'active ion transport' across the root plasma membrane derives from precise analyses of uptake 'isotherms' describing nutrition as a function of ion concentration in the root medium. Attempts to introduce feedback mechanisms, as required to model whole-plant response to the environment, are reviewed. Similarly, the response of plant photosynthetic capacity to leaf nitrogen status is extremely rapid and the role of nitrogen in regulating photosynthesis seems to hold for a large number of species. Therefore, it appears possible to introduce nitrogen regulation on leaf photosynthesis, thus allowing better simulations of plant growth under nitrogen limiting conditions. Long-time scale studies are dealt by agronomists and have long been the basis of fertilization advice. They attempt to predict crops' mineral nutrient requirements over the entire cycle from the empirical knowledge of 'general laws' governing crop growth. Recent advances propose to manage nutrition on the basis of crop structure independently from species and give opportunities to develop mechanistic concepts at this time scale. For nitrogen, this has been formalized extensively in crops such as cereals and grasses. It deserves to be carefully looked at for horticultural crops. These models also provide a sound basis to diagnosis through plant analysis. In horticultural agrosystems, such as those found for hydroponic cultures under commercial glasshouses, the use of on-line sensors is currently an alternative to crop models, since fertilization is induced by the immediate response of the sensors. This practice made possible by technological breakthrough is meant to correct drifts but lacks anticipation. (C) 1998 Elsevier Science B.V.