MODELING 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-t ime scale studies are mostly dealt by plant physiologists with the pro spect of building mechanistic models. They describe elementary plant f unctions implicated in, or dependent on ion uptake, with the goal of e xplaining the mechanisms underneath the functions. The concept of 'act ive ion transport' across the root plasma membrane derives from precis e 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 environme nt, are reviewed. Similarly, the response of plant photosynthetic capa city to leaf nitrogen status is extremely rapid and the role of nitrog en in regulating photosynthesis seems to hold for a large number of sp ecies. Therefore, it appears possible to introduce nitrogen regulation on leaf photosynthesis, thus allowing better simulations of plant gro wth under nitrogen limiting conditions. Long-time scale studies are de alt by agronomists and have long been the basis of fertilization advic e. They attempt to predict crops' mineral nutrient requirements over t he entire cycle from the empirical knowledge of 'general laws' governi ng crop growth. Recent advances propose to manage nutrition on the bas is of crop structure independently from species and give opportunities to develop mechanistic concepts at this time scale. For nitrogen, thi s 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 cul tures under commercial glasshouses, the use of on-line sensors is curr ently 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 antic ipation. (C) 1998 Elsevier Science B.V.