Nitrogen (N) Nitrogen deficient potato plants generally show a light green to yellow colouring of the whole plant. Since N is mobile in  the plant, deficiency symptoms will first appear on the older bottom leaves and then spread to the rest of the plant. N  deficiencies will result in a shorter growing season, which will negatively affect tuber yield.  Optimum N levels in the plant depend on the growth stage, but leaf deficiency symptoms can generally be expected  when NO3- levels in the leaf petioles drop below 0.5 to 0.8 % (on a dry mass basis). N deficiencies can be prevented  by applying sufficient N to the soil at planting, as well as through N top dressings during the growing season. A wide  range of N sources are commercially available. 
Nutrient Deficiencies: Macro nutrients - Nitrogen (N)