Nitrogen deficiency or excess

• Role in the plant : nitrogen (N) is involved in the production of proteins, nucleic acids and in the photosynthesis. A sufficient supply of nitrogen is therefore important during the early stage of leaf formation and haulm growth but also later during tuber bulking. Conversely, an excessive application of nitrogen can inhibit tuber initiation, reduce the yield and limit the dry matter content. At the end of the vegetative period, an over-supply of nitrogen can delay the maturation of the tubers and favours skin peeling, which in turn can impair the quality of the tubers and their storage ability.

• Symptoms of deficiency: in the case of nitrogen deficiency, the colour of the foliage is lighter. In severe shortage, leaves are pale yellow or chlorotic (photos 1 to 3) and the leaf mass is reduced (photo 2). As nitrogen is a mobile nutrient, symptoms of deficiency usually concern the whole plant.

• Excess nitrogen delays maturity and favours the development of the canopy. A high haulm volume increases the humidity around the basal parts of the plants and may enhance the plant susceptibility to certain diseases such as late blight, blackleg or white mould.