Nitrification and Denitrification near a Soil–Manure Interface Studied with a Nitrate‐Nitrite Biosensor

Abstract

A two‐layer system of cattle ( Bos taurus ) manure and soil was used to study the development of nitrification and denitrification processes associated with the oxic–anoxic interface of soil and manure over a period of 18 d. By use of microsensors, depth profiles of O 2 and nitrate plus nitrite NO − x were measured. We observed an initial depletion of NO − x originally present in the soil, followed by an increase after ∼1 wk caused by the activity of nitrifying bacteria. Fluxes of NO − x from the soil into the manure were calculated from NO − x profiles and compared with measurements of N 2 production. Generally, NO − x fluxes and N 2 production were concordant. Denitrification (NO − x consumption) was closely coupled to nitrification until Day 18, when NO − x accumulated in the anoxic zone and therefore no longer seemed to limit denitrification. Maximum denitrification rates were measured at Day 9/10 and reached 732 and 497 nmol N m −2 h −1 when measured as NO − x flux and N 2 production, respectively. An experiment was set up to investigate the temporal change in NO − x profiles when nitrification was inhibited by acetylene. Profiles of NO − x were measured at 0, 2, 4, 8, 16, 24, and 48 h of incubation with 1% acetylene. Calculated NO − x fluxes were 39% of the original rates after 2 h and only 2% after 48 h. Thus, this experiment stresses the importance of very short incubation time when using the acetylene inhibition technique to measure denitrification rates.