Nickel is the most recently discovered micronutrient; it is required in small amounts by plants.
Leguminous crops like bean and cowpea require more Ni than other crops because Ni plays an important role in nodulation and N fixation.
Nickel is unique among plant nutrients because its functions in plant growth and development were described in detail before Ni was added to the list of essential elements. Nickel is a key component of selected enzymes (described below) involved in N metabolism and biological N fixation. Plants suffering from Ni deficiency show necrosis initiating from the tip of the leaf (Figures 1–4). This symptom can be reversed or corrected by applying a dilute Ni solution (Figure 5).