Effects of nitrogen deficiencies on autumnal growth of oilseed rape

Several field experiments were carried out to define the effects of temporary N deficiency in autumn on the growth and yield of winter oilseed rape. N deficiencies are described in terms of nitrogen nutrition index (NNI) i.e. methodologies of Lemaire et al. (Proceedings of the XVI International Grassland Congress, Nice, France, 1989, p. 179) and Lemaire and Gastal (In: G. Lemaire (Ed.), Springer, Berlin, Diagnosis of the Nitrogen Status in Crops, 1997, p. 3). The growth components analysed were shoot and tap root biomass, leaf area index (LAI) and radiation use efficiency (RUE). In all the experimental conditions, N deficiencies were severe (NNI near 0.60) and had significant effects on all growth components. These growth variables and NNI were fitted by various functions. The effects of N stress on winter oilseed rape are discussed and compared to another crop. Despite severe autumn N deficiencies, no difference in yield was apparent because these deficiencies probably allow all the time enough growth in autumn to ensure sufficient regrowth in spring.