Turnover of Nitrogen

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Turnover of Nitrogen

The Turnover of Nitrogen

Just as carbon is the key elements for the synthesis of carbohydrates, so is nitrogen for he synthesis of protein. The atmosphere is a vast reservoir of nitrogen but the N₂ of the atmosphere must necessarily combine with H₂ or O₂ before it can be assimilated by higher plants. The inert atmospheric nitrogen occupies approximately 75% by weight, and 78% by volume of the atmosphere and totals 3.8 x 10¹⁵ tonnes.

However, the amount of nitrogen in the biosphere is dependent on the rates of transfer within the nitrogen cycle and can be estimated only within broad limits. Some authors have estimated that 400 x 10⁶ t N/yr by are transferred between the various nitrogen pools, with losses of 215 x 10⁶ t N/yr by denitrification and 185 x 10⁶ t N/yr by volatilization and combustion.

Estimated returns are 200 x 106 t N/yr in precipitation (mainly volatilized ammonia), 170 x 106 t N/yr from biological fixation and 30 x 10⁶t N/yr from industrial fixation. These figures differ from those of others who estimate a biological nitrogen fixation rate of 92 x 10⁶ t N/yr. Nevertheless, these data provide a rough estimate and point out unmistakably that nitrogen fixed by biological means is more than three times that of industrial fixation.

Biological fixation of nitrogen takes place in root nodules of legumes and also on land and water y means of free-living bacteria and microalgae. Of minor importance is the fixation of atmospheric nitrogen through precipitation and lightning. Man has recently intervened in the nitrogen cycle by industrial fixation of N₂in fertilizer factories where nitrogen and hydrogen are combined at high temperature and pressure with the help of an inorganic catalyst to produce ammonia. And pressure with the help of an inorganic catalyst to produce ammonia. Denitrification processes, almost of equal magnitude, breakdown nitrates and return elemental nitrogen into the atmosphere making the cycle complete.

The Nitrogen Cycle in the Biosphere

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