Azodyn: a simple model simulating the date of nitrogen deficiency for decision support in wheat fertilization

A dynamic soil–crop model was developed to predict the date on which N deficiency occurs for winter wheat crops in the temperate climate of Northwest Europe. It is based on the daily simulation of soil N supply and crop N requirement for the period during which N-fertilizer is usually applied to wheat crops, the end of winter until flowering. The soil sub-model was derived from the `balance-sheet method' used in France for nitrogen fertilization recommendations. It describes the net mineralization of various sources of organic matter (soil humus, crop residues, organic products). The crop sub-model simulates crop biomass production and its nitrogen content using a radiation use efficiency model and a critical dilution curve for nitrogen content. Both soil and crop sub-models require few parameters and inputs, most of which are readily available on commercial farms, together with daily climatic data. The model tested with various rates and timings of N application in three experiments accurately simulated the date on which nitrogen deficiency began in wheat crops. The interest in using the model for tactical and strategic approaches is discussed.