Contents



Preface

Nitrogen (N) is the most abundant gas in the Earth's atmosphere, although it is exceptionally unreactive. Biological nitrogen fixation (BNF), the process by which gaseous N2 is converted into ammonia (NH3) via the enzyme nitrogenase, is crucial for the availability of nitrogen in the terrestrial ecosystem. Some bacteria have the remarkable capacity to fix atmospheric nitrogen to ammonia under ambient conditions, a reaction only mimicked on an industrial scale by a chemical process. This microbiological process converts atmospheric nitrogen into a plant-usable form, thus decreasing the necessity of the use of chemical fertilizers in crop production. In many systems, N fixers have driven the accumulation of fixed N on long time scales, bringing N supply dose to equilibrium with other potentially

BNF includes symbiotic (nodule formation) and free-living bacteria N fixation, defined as N fixation occurring without formal plant–microbe symbioses. The ability of microorganisms to use nitrogen gas as the sole nitrogen source and engage in symbioses with host plants confers many ecological advantages. However, it also incurs physiological penalties. BNF is highly regulated at the transcriptional level by sophisticated regulatory networks that respond to multiple environmental cues.

The present book chapters in this volume cover approaches different aspects related to of this fantastic phenomenon, such as biofertilizer, organic nitrogen in agricultural systems, nitrogen fertilization for sustainable crop production, and

I would like to thank my wife Fernanda, my daughter Maria Eduarda and my son João Henrique for making my life happier. I also thank my deceased father Angelo Sidney Rigobelo, who lives in my mind and in my heart every day of my life.

Brazilian Agricultural Research Corporation - EMBRAPA – Campo Grande MS –

**Everlon Cid Rigobelo**

**Ademar Pereira Serra**

Brazil

Brazil

Department of Plant Production,

Department of Plant Production,

Universidade Estadual Paulista – FCAV – Jaboticabal SP –

limiting resources.

others.
