ABSTRACT
Among the mineral nutrient elements, nitrogen (N) most often limits the growth and yield of nonleguminous crop plants, which require relatively large quantities of N (from 1.5 to 5% of the plant dry weight) for incorporation into numerous organic compounds. These compounds include proteins, nucleic acids, chlorophyll, and growth regulators, all of which have crucial roles in plant growth and development. The N composition of plant tissues also has important nutritional consequences, since plants are a major source of proteins in the diet of humans and animals. Because N deficiency can seriously decrease yield and crop quality, elaborate steps are often taken to assure that adequate N levels are available to plants.
