A comparison of the threshold concentrations of DCD, DMPP and nitrapyrin to reduce urinary nitrogen nitrification rates on pasture soils: A laboratory study

 

Context: Using nitrification inhibitors (NIs) for the targeted management of urine patches, to reduce nitrous oxide (N₂O) emissions, requires determining the threshold concentrations of the NIs in urine for effective nitrification inhibition.

Aims: This study comparatively assessed the threshold concentrations of three NIs: dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP) and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) to reduce urinary nitrogen (N) nitrification rates on two contrasting pasture soils.

Methods: Four rates of each NI (3–27 mg DCD kg⁻¹ soil, 1–13 mg DMPP kg⁻¹ soil and 1–14 mg nitrapyrin kg⁻¹ soil) were added to urine-amended soils and incubated at laboratory room temperature. The amended soils were sampled periodically to monitor changes in mineral-N concentrations.

Key results: The threshold concentration of DCD (3 mg kg⁻¹ soil, lowest rate tested) was lower than that of nitrapyrin (5–7 mg kg⁻¹ soil) and DMPP (13 mg kg⁻¹ soil, highest rate tested) on both soils. Greater NI effectiveness corresponded to greater NI persistence, with higher (P < 0.05) half-life values observed for DCD (16 ± 2 days, mean ± s.e.) compared with nitrapyrin (10 ± 2 days) and DMPP (9.2 ± 0.3 days). All three NIs persisted longer (P < 0.05) with higher application rates.

Conclusions: Compared with DCD and nitrapyrin, a higher DMPP concentration was required to effectively inhibit urinary N nitrification rates in the pasture soils.

Implications: Choosing the ideal application rate of NIs to inhibit nitrification under field condition, and hence mitigate N₂O emissions from urine patches, requires consideration of the factors that affect NI loss.