Conclusion

Nickel is the latest element to be classified as essential for plant growth in both laboratory and field conditions and an absolute requirement for nickel fertilizer under field conditions in perennial species growing in the southeast of the United States has now been established. Nickel clearly has a significant effect on the productivity of field-grown, nitrogen-fixing plants, those in which ureides are a significant form of nitrogen and those utilizing urea as a primary nitrogen source. The symptoms of nickel deficiency in barley, wheat, and oats observed by Brown et al. (1) and Wood et al. (2) are consistent with the observations made in nickel-deficient animals and are indicative of a role of nickel in nitrogen metabolism that cannot be easily explained through an exclusive role of nickel in urease. This finding in combination with the diverse known functions of nickel in bacteria suggests that nickel may indeed play a role in many, yet undiscovered processes in plants.