Overview and Case studies on Biological Nitrogen Fixation: Perspectives and Limitations

Nitrogen is an essential plant nutrient. It is the nutrient that is most commonly deficient in soils, contributing to reduced agricultural yields throughout the world. Nitrogen can be supplied to crops by biological nitrogen fixation (BNF), a process which is becoming more important for not only reducing energy costs, but also in seeking more sustainable agricultural production. Nitrogen fixing micro-organisms could therefore be an important component of sustainable agricultural systems. There are several significant reasons to seek alternatives to fertilisers that provide chemically fixed nitrogen: Ø Environmental Nitrogen fertilisers affect the balance of the global nitrogen cycle, and may pollute groundwater, increase the risk of chemical spills, and increase atmospheric nitrous oxide (N2O), a potent “greenhouse” gas. Ø Energy The primary energy source for the manufacture of nitrogen fertiliser is natural gas together with petroleum and coal. On the contrary, the energy requirements of BNF are met by renewable sources such as plant-synthesised carbohydrates rather than from nonrenewable fossil fuels. Ø Sustainability Longterm sustainability of agricultural systems must rely on the use and effective management of internal resources. The process of BNF offers an economically attractive and ecologically sound means of reducing external nitrogen input and improving the quality and quantity of internal resources. Ø Nutrition It is estimated that about 20% of food protein worldwide is derived from legumes. There are more than 13,000 described species of legumes and for only 3,000 species examined more than 90% were found to form root nodules. Because few have been exploited for food, there is the prospect that the utilisation of legumes could be expanded substantially. It is anticipated that increasing demographic pressure and food demand will require the exploitation of BNF as a major source nitrogen for plant protein production.