Biotechnology of Nitrogen Acquisition in Rice - Implications for Food Security

The intensive irrigated rice farms in the lowlands of southern Asia are the world’s most important agricultural systems, covering some 79 million hectares, and accounting for approximately 70% of global rice production. While rice yields are sufficient to meet current human needs, they must increase by 60% within the next 30 years, if present projections for human population growth are correct (Ladha and Reddy 2003). Among the factors compromising the realisation of rice yield potential in the field, the supply and uptake rates of nitrogen are recognised as being among the foremost (Ladha and Reddy 2003). For instance, Horie et al. (1997) showed that the number of spikelets produced by rice plants was closely related to the plants’ N status, and Witt et al. (1999) showed a similarly strong relationship between grain yield and plant N status.

A different approach to the issue of nitrogen and rice yield, and the one which is the main subject of this chapter, involves an examination of the physiology of rice-nitrogen relations, at whole-plant, cellular, biochemical, and genetic levels of organisation. This information is vital to the implementation of conventional and recombinant-DNA breeding methods to increase both the yield of the rice crop, and its agronomic N-use efficiency (i.e. the yield increment relative to N fertiliser input). This chapter will discuss several important aspects of rice-nitrogen relations, focusing on four main topics: 1) biological N fixation, 2) N uptake, 3) N assimilation and, 4) points of intersection between photosynthesis and plant N use.