Multiannual evolution of the nutrition index in relationship with the annual balances.

Nutrition index are used on a wide scale for the diagnsosis of the mineral nutrition of the grasslands and to facilitate the decisions regarding their fertilisation mode.In literature are available few data regarding the inter-annual evolution of the nutrition indexes in relationship with the cumulated mineral balances. The problems that are coming from are to find out the measure in that those indexes are able to provide piece of information on the evolution of the N and P supplies level in the case that the mineral balance is positive or in the case in that the mineral balance is negative. The experimental fields were set by the Orphee team (INRA Toulouse) on two grassland types different from the pedological and climatic point of view, placed in Erce in Central Pyrenees in 1999 (0° east, 43° north) and in Gramond in Massif Central in 1998 (2° east, 44° north). There were applied four treatments: N0P0, N0P1, N1P0 et