The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is used to limit nitrogen (N) losses incurred following nitrification of applied N fertilisers. Inhibitor efficacy changes with soil conditions including pH and organic matter (OM) content, both of which can be stratified down the soil profile. An incubation study was conducted using acidic soil that exhibited pH stratification. Soil samples were collected from the field in 2 cm depth increments to a depth of 10 cm. Two liming treatments were applied to each depth where the pH_Ca was raised above 6 or left in its initial acidic state. Nitrogen treatments (urea ammonium nitrate (UAN) with and without DMPP) were applied to each liming treatment per depth and incubated for four weeks. Destructive sampling for mineral N, DMPP concentration and pH occurred every week. The abundance of nitrifiers was determined using semi-quantitative real-time polymerise chain reaction (PCR) targeting the amoA gene at weeks 0, 1 and 4. Liming significantly increased nitrification rates and bacterial amoA gene abundance. Results showed the top 0–2 cm recorded the largest population of bacterial nitrifiers. Changes in pH influenced the composition of nitrifiers present in the soil. Bacterial nitrifiers were absent from the 8–10 cm soil layer in unlimed soils (pH_Ca 4.25) but liming caused an increase in gene abundance. Archaeal amoA gene abundance was highest in unlimed plots at 4–8 cm depth although populations decreased over the incubation period and also with lime application. DMPP effectively inhibited nitrification in limed plots, however no significant difference existed between UAN and DMPP treatments for unlimed treatments. DMPP successfully decreased bacterial amoA gene abundance in all depths that were limed but not in unlimed soils. Decreases in inhibitor concentrations occurred within one week in the 0–2 cm layer possibly due to bacterial decomposition associated with greater OM concentration at the soil surface. This study highlighted that DMPP use is more effective in relatively neutral soils and liming will change the abundance and distribution of nitrifiers within the top 10 cm of soil.

硝化抑制剂3,4-二甲基吡唑磷酸酯（DMPP）用于限制氮肥施用后硝化氮的损失。抑制剂的功效随土壤条件的变化而变化，包括pH值和有机物（OM）含量，两者均可沿土壤剖面分层。使用显示pH分层的酸性土壤进行孵育研究。从田间以2 cm的深度递增到10 cm的深度收集土壤样品。在pH _Ca值的每个深度进行两次石灰处理升高至6以上或保持其初始酸性状态。将氮处理（有和没有DMPP的尿素硝酸铵（UAN））应用于每个深度的石灰处理，并孵育4周。每周进行破坏性采样，以检测矿物质氮，DMPP浓度和pH。使用针对amoA基因的半定量实时聚合链反应（PCR）在第0、1和4周确定硝化剂的丰度。石灰化显着提高了硝化率和细菌amoA基因的丰度。结果显示，最高的0–2 cm处记录了最大数量的细菌硝化器。pH值的变化会影响土壤中硝化剂的组成。在无盐土壤（pH _Ca）中8–10 cm的土壤层中没有细菌硝化剂4.25），但石灰限制增加了基因丰度。尽管在孵化期和施用石灰的情况下种群减少，但古菌在4-8 cm深度的无土块中amoA基因的丰度最高。DMPP有效地抑制了石灰土地上的硝化作用，但是对于非限制处理，UAN和DMPP处理之间没有显着差异。DMPP成功降低细菌amoA石灰覆盖的所有深度的基因丰度都很高，但是在未加盐的土壤中却没有。0-2 cm层中的抑制剂浓度在一周之内下降，这可能是由于细菌分解与土壤表面较高的OM浓度有关。这项研究强调指出，在相对中性的土壤中使用DMPP更为有效，而石灰会改变硝化剂在土壤表层10 cm内的丰度和分布。