Regulators of Ammonium Oxidation

FIGURE 8.37 Ammonium oxidation under ideal conditions where very little nitrite accumulates as an intermediate product. Second step of nitrification is inhibited resulting in accumulation of nitrite. 

Ammonium concentration High concentration of ammonium nitrogen has been found to inhibit the activity of Nitrobacter, particularly at high pH values, probably due to production of free ammonia. However, in wetlands, ammonium levels are never high enough to affect nitrifiers in an adverse manner. 

Oxygen availability Oxygen is essential for the obligate aerobic requirements of nitrification. However, the actual limit is more dependent on the oxygen flux into the system rather than on the oxygen level at a given time. 

Temperature The optimum temperature for uitrificatiou in pure cultures ranges from 25 to 35°C and in soils from 30 to 40°C. Lower temperatures (below 15°C) have a much more drastic effect ou uitrificatiou rate compared to the temperatures between 15 and 35°C. (Kadlec and Reddy, 2001). 

Cation exchange capacity The CEC plays an important role in buffering rapid changes in ammonium concentration in soil solution therefore, nitrification rates are slower in soils with high CEC such as clay loam soils. Again, diffusion of ammonium to microbes may be slower in soils with high CEC as these soils maintain low ammonium levels in soil pore water. 

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