BIOASSAY TO DETERMINE THE EFFECT OF ORGANIC-MATTER AND PH ON THE EFFECTIVENESS OF NITRAPYRIN (N-SERVE) AS A NITRIFICATION INHIBITOR

The aerobic incubation procedures commonly used in biological studies have several disadvantages to assess inhibition of nitrification. Therefore, a more suitable procedure was developed. It involves pre-incubating soil samples treated with (NH4)2HPO4 to establish a uniform population of nitrifiers before the addition of the nitrification inhibitor or other amendments. Through successive additions of (NH4)2HPO4, a constant nitrification rate is maintained. This system enables direct comparison between treatments throughout the experiment. Data obtained using this procedure indicated that sorption of Nitrapyrin (NI) is a major factor decreasing the effectiveness of NI in organic soils. Loss of NI by volatilization also decreased its effectiveness, while the relative inhibition by NI was found to increase as soil pH increases. The greater susceptibility of nitrifiers to NI at high pH may be due to a relationship between pH and nitrifier ecology. © 1979.