Study on the fate of fertilizer nitrogen during summer maize season based on high abundance of ¹⁵N under application of urease/nitrification inhibitors

Objectives The purpose of this paper was to investigate the fate of fertilizer nitrogen under the application of urease/nitrification inhibitors in summer maize in North China Plain by using high abundance ¹⁵N isotope tracer method.

Methods The summer maize field experiment was conducted from June 25 to October 9 of 2022 in Langfang, Hebei Province. The experiment contained five treatments: no nitrogen fertilizer control (CK), merely urea application (U), combined application of urea with urease inhibitor (UI), nitrification inhibitor (NI), and both of urease and nitrification inhibitor (UI+NI). The cumulative NH₃ volatilization and N₂O emission were monitored to calculate the gaseous loss of fertilizer nitrogen. The N uptake by plant, soil fertilizer N residues were investigated at harvest.

Results Compared with merely urea treatment, UI, NI and UI+NI treatment increased the N absorption in the above ground of maize by 39.7%, 33.1% and 41.8%, thus significantly increased the N recovery rate by 12.5, 6.8 and 12.3 percentage points, respectively, and the enhancement effect of UI and UI+NI were higher than that of NI. Compared with U, UI and UI+NI increased soil N residue by 35.6% and 45.7%. NI did not reduce the NH₃ volatilization obviously, while UI and UI+NI significantly decreased that by 14.3% and 11.6%, respectively. All the UI, NI and UI+NI treatments reduced cumulative N₂O emission significantly, with the reduction rate of 17.2%, 19.9%, and 34.5%, respectively, and UI+NI treatment was recorded significantly higher reduction rate than UI and NI by 20.9% and 18.2%, respectively.

Conclusions In the typical fluvo-aquic soil of North China Plain, combining application of urea with urease/nitrification inhibitors on summer maize could significantly increase the nitrogen absorption of summer maize. Urease inhibitor significantly increases fertilizer nitrogen residues in soil, reduces NH₃ volatilization and cumulative N₂O emission, while nitrification inhibitor mainly reduces the cumulative N₂O emission. The combined application of urease and nitrification inhibitors shows significantly better effect than the respective application in increasing N uptake, reducing gaseous loss of nitrogen fertilizer and improving the nitrogen fertilizer utilization rate, so is recommended for the maize fertilization in the test area.