Abstract: With aerobic incubation test, this paper studied the effects of 3,5-dimethylpyrazole phosphate (DMPZP) on soil nitrification, taking dicyandiamide (DCD) as reference. The results indicated that when the dosage was 1.0% of applied N, DMPZP could significantly inhibit the oxidation of soil ammonium, increase soil NH₄⁺-N concentration, and decrease soil NO₃^--N concentration. The inhibitory effect of DMPZP increased with its increasing dosage. DCD showed a higher efficacy when its dosage was the same with DMPZP, but a lower efficacy when the DMPZP was applied twofold. However, the efficacy of equimolar DMPZP was significantly higher than that of DCD, because of the smaller molecular weight of DCD. The highest inhibitory effect of DMPZP was observed during the period of 7-14 days after its application, with an inhibition rate higher than 30%. Compared with the control, the apparent inhibition rate was decreased by 29.3% and 41.7% on the 7^th day, and by 18.6% and 34.3% on the 14^th day when the application rate of DMPZP was 1.0% and 2.0% of applied N, respectively. DMPZP could also slow down the falling rate of soil pH, but no significant difference was observed between the treatments of applying DMPZP and DCD.

Key words: Wheat varieties (lines), Indole alkaloids, Tillering stage, Elongation stage, Flag leaf, Ear