Methods for determining the nitrogen fertiliser requirements of some major arable crops

Abstract : The paper provides an overview of the methods used in France to enable the calculation of forecast nitrogen (N) fertilizer recommendations, taking account of soil N availability and plant requirements. These methods, considered as frameworks, and some tools derived from the methods, require soil N measurements or/and plant measurements. The example of a tool based on the balance-sheet method (Azofert®) is emphasised. Plant measurements also enable more reliable predictions of plant N requirements to be made, as shown by a tool designed for oilseed-rape ('Réglette colza'). Moreover, plant measurements based on N nutrition status in crops are used to monitor crops and to adjust fertilisation during crop growth in situations where nitrogen applications are split. In the last part, the authors discuss the use of the tools designed for decision-making, to help farmers to adjust fertilisation more accurately. They also highlight the necessary conditions for designing methods and tools for sustainable nitrogen management in the future.