THE VARIABILITY OF NITRIFYING ACTIVITY IN FIELD SOILS

The effect of pH on the activity of nitrifying organisms was examined in pasture soils ranging in pH from 4.9 to 7.3, using a short-term nitrification assay (SNA). The optimum pH for nitrifier activity (pHopt) was generally close to the soil pH, suggesting that the indigenous nitrifier populations adjusted to the prevailing soil pH. A consequence was that the SNA at the soil pH (SNApH) bore a near 1:1 relationship with the SNA at the pHopt (SNAopt) over a wide range of SNA values. The effect of soil moisture tension on the SNA was less pronounced than that of pH, but an optimum occurred around pF 3.4. © 1990 Kluwer Academic Publishers.