REVIEW Towards an explanation of crop nitrogen demand based on the optimization of leaf nitrogen per unit leaf area

Abstract

An area of plant science that is still uncertain is precisely what determines plants' demand for nitrogen (N), that is the amount of N they need to take up from the soil to meet their requirements for potential growth and synthesis of new tissue. A robust and unequivocal physiological basis from which to determine N demand is lacking. Yet N dominates plant nutrition. No nutrient is needed in larger quantities and, in most environments, no nutrient is in such limiting supply. Knowledge of the factors governing N demand is essential to predict the needs of crops under a wide range of field situations, so that growers can be given more reliable fertilizer recommendations (Greenwood 1982; van Keulen et al. 1989). This is important, not just for economic reasons, but because of the risks to the environment that can arise from the over-application of N fertilizers, in particular the problem of nitrate leaching (Addiscott et al. 1991).