ABSTRACT
I. INTRODUCTION Nitrogen is one of the most essential elements for plant growth and development. It is a constituent of many biomolecules such as proteins, nucleic acids, amino acids, coenzymes, vitamins, and pigments. Because of its high requirement by plants and its complete absence in the bedrock, it has a special place in plant nutrition. Nitrogen supply in the soil is often the most important factor limiting plant growth and yield. In the soil, N availability is due to the application of N fertilizers, biological action of N2 fixing organisms, or natural fertilization. With the advent of modern agricultural practices, inorganic N fertilizers have become the major input to the soil. In our quest to achieve sustainable food production, to meet the increasing food requirements for global population, excessive uses of various forms of N fertilizers are still likely in the near future.
