Nitrogen source regulates soil nitrification and nitrogen losses more than nitrification inhibitor and herbicide in a loamy sand soil

Authors: NEELS, WILLIAM - University Of Nebraska; JHALA, AMIT - University Of Nebraska; Jin, Virginia; PATEL, SWETABH - University Of Nebraska; MAHARJAN, BIJESH - University Of Nebraska; IQBAL, JAVED - University Of Nebraska

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Enhanced efficiency fertilizers (EEFs) could decrease nitrogen losses that pollute the environment. It is unknown how EEFs interact with herbicides, which have been shown to impact soil microbes involved with nitrogen cycling. In this laboratory study, we compared the effects of nitrification inhibitors on different combinations of fertilizers and herbicides in a loamy sand soil. Fertilizer source had a stronger effect on soil nitrification rates, ammonia volatilization rates, and nitrate leaching than nitrification inhibitor (inconsistent effects) or herbicide (no effects). Fertilizer type, nitrification inhibitor, and herbicide had no impacts on short-term nitrous oxide emissions.

Technical Abstract: Increased environmental nitrogen losses have prompted the use of enhanced efficiency nitrogen fertilizers, including nitrification inhibitors. The comparative effects of these nitrification inhibitors to conventional nitrogen fertilizer sources and herbicides on soil nitrification and nitrogen losses are poorly understood. We evaluated the impact of a nitrification inhibitor (Instinct NXTGEN), two nitrogen fertilizer sources (broadcast urea vs. injected aqueous ammonia), and a pre-emergence herbicide (Acuron) on 1) soil nitrification through a 25 day-soil incubation study, and 2) NH3 volatilization, NO3-N leaching, and N2O-N emissions through a 31-day soil column study in loamy sand soil. In both experiments, the treatments included a combination of nitrification inhibitor vs. no herbicide. Results indicated that nitrogen source had a more significant effect on reducing nitrification (33% lower with injected aqueous ammonia vs. surface broadcast urea) than nitrification inhibitors (4% lower with inhibitor vs. without inhibitor) and herbicide (no effect). Injected aqueous ammonia decreased NH3 volatilization by 87% compared to surface broadest urea, while nitrification inhibitor had an inconsistent effect on NH3 volatilization across both N sources. Injected aqueous ammonia had 39% higher cumulative nitrogen (NO3-N + NH4-N) leaching than urea, while nitrification inhibitor had an inconsistent effect on NO3-N leaching across both N sources. No significant treatment effect was observed on N2O-N emissions. The herbicide did not affect measured parameters. These results indicate that nitrogen source significantly regulates soil nitrogen losses more than nitrification inhibitors and herbicides.