Nitrification and abundance of nitrifier bacterial as effected by inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) in five different soils

Low nitrogen use efficiency (NUE) is a global problem in crop production, and agriculture of Iran is not exempt in this regard. Nitrogen (N) fertilizers as a source of nitrogen can be very effective in water, soil and air environmental pollution. Nitrification is a key process in agricultural ecosystems since it results in changes of ammonium to nitrate and eventually loss of considerable amounts of soil nitrogen through leaching and denitrification. The application of nitrification inhibitors (NI) together with nitrogen fertilizers is a strategy to reduce N losses. Thus, the objective of this study were to evaluate the effect of inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) on nitrification rates and nitrification inhibition percentage in some soils of Iran containing representing differences in organic matter content and texture.

An incubation experiment was conducted to evaluate the effect of DMPP on nitrate and ammonium concentration changes in different times and abundance of ammonium (AOB) and nitrite (NOB) oxidizer bacteria in five soils with different texture and organic carbon (O.C). The treatments of experiment included NI at three levels (without N and NI, 200 mg/kg N as ammonium sulfate without NI, and 200 mg/kg N as ammonium sulfate containing 0.8 % NI), five soil types (sandy loam 1 with 0.58% O.C, sandy loam 2 with 0.3% O.C, loam with 0.73% O.C, clay loam with 0.87% O.C, clay with 1.47% O.C), and five sampling times (0, 14, 28, 42, and 56 day).

The results showed that application of N containing DMPP compared to N without DMPP in all soils had significant effect (P<0.001) on reducing nitrification, which was reduced 44.7% on average. DMPP efficiency on nitrification inhibition in experimented soils had significant difference, indicating that nitrification occurs rapidly in soils containing more clay and O.C compared to soils with more sand and low O.C. Nitrification inhibition percentage after 56 day incubation in SL1, SL2, and L were 57%, 46%, and 12%, but in two other soils were about zero. Also there were a positive significant correlation between abundance of AOB and NOB with nitrate concentration (r = 0.6), O.C content (r = 0.9), and total soil N (r = 0.9).

soil nitrification rate are different under influence of factors like soil textural properties and soil O.C content, and DMPP efficiency had inverse relationship with some soil properties including clay%, O.C content, and nitrifier bacterial population. Further these properties can be used in predicting the short term effects of inhibitors.