Biochemistry of nitrification in soil

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Abstract
When a soil is perfused with (NH4)2SO4 soln., little or no nitrification takes place in the perfusate or soil soln. Nitrification takes place at soil surfaces where NH4+ is combined or absorbed. Addition of Ca++ to a perfusate, the rate of nitrification is diminished in proportion to amt. of NH4+ displaced from the soil surface by base exchange with the Ca++. The ratio of soil-absorbed NH4+ to the total NH4+ in a soil-perfusate system remains approx. constant. The rate of nitrification in soil is proportional to fraction of total NH4+ absorbed on the base-exchange complexes of the soil, independent of NH4+ in soln. and increases with amt. of soil. Nitrifying bacteria nitrify on the surfaces of soils, in the vicinity of the receptor sites where NH4+ is combined. Soils which have been enriched with nitrifying bacteria by previous perfusion with (NH4)2-SO4 show subsequently linear courses of nitrification and are termed bacteria-saturated soils and do not show a time lag.