Agronomical and physiological aspects of ammonium and nitrate nutrition of plants

Field studies comparing yield responses of crops treated with different nitrogen fertilizer types have led to very contradictory results. This can be explained by the fact that the application of different forms of nitrogen map affect plant growth via numerous processes in the soil and within the plant. In this review the significance of these processes for nutrient availability in soil are briefly outlined. Then, data from literature and own results are used to show that an enhanced ammonium supply may promote certain yield components such as the number of ears per Plant in wheat or the number of kernels per plant in maize whereas other yield components such as the number of grains per ear in cereals or the number of tillers in linseed may he adversely affected by ammonium supply. These different effects of ammonium and nitrate supply on yield structure of plants are related to physiological changes in the plant using a model.