Biological Nitrogen Fixation by Legumes - Nitrogen Management in Crop Production - page 317

FIGURE 7.10 Showy crotalaria root growth at different N treatments. Left to right 0 mg N kg −1 ,
0 mg N kg −1 + Bradyrhizobial inoculants, 100 mg N kg −1 + Bradyrhizobial inoculants, and 200 mg N kg −1 .
(Adapted from Fageria, N. K. et al. (In press). Commun. Soil Sci. Plant Anal .)
FIGURE 7.11 Calopo root growth at different N treatments. Left to right 0mgNkg −1 ,
0 mg N kg −1 + Bradyrhizobial inoculants, 100 mg N kg −1 + Bradyrhizobial inoculants, and 200 mg N kg −1 .
(Adapted from Fageria, N. K. et al. (In press). Commun. Soil Sci. Plant Anal .)
7.8 CONCLUSIONS
The majority of biological fixed N available for agriculture is formed by rhizobia in symbiosis with
legumes. It is known as dinitrogen fixation (N 2 ). Biological N fixation or dinitrogen (N 2 ) fixation
is one of the most important biochemical reactions occurring in growing legumes for life on the
earth. It ranks second only to photosynthesis in importance as a biological fixation reaction and,
as evidenced by this treatise, has been the subject of intensive research at all levels of interest. N is
also fixed by some nonlegume crops, but it was not discussed in this chapter. Globally, a significant
amount of N is fixed biologically each year. Globally, biological N fixation has been estimated to
amount to at least 139 million metric tons of N per year. This amount is much more than the N
produced by the fertilizer industry, which is estimated to be about 90 million metric tons per year.