How does fall-applied nitrogen fertilizer influence soil-emitted nitrous oxide emissions during the over-winter and spring thaw period in the semi-arid Prairies?

Project Summary

Overview

Nitrogen fertilizer applications are a substantial source of cropping system nitrous oxide (N₂O) emissions – a particularly potent greenhouse gas and a major contributor to stratospheric ozone depletion. In Canada, up to 90% of annual N₂O emissions from cropping systems can occur during the overwinter and spring snow melt period (non-growing season).

Farmers are under increasing pressure to minimize greenhouse gas emissions from their production systems. Strategies that would reduce emissions during this time period would be an important opportunity to achieve this goal as well as to realize greater benefit from their nitrogen fertilizer.

Fall-applied nitrogen fertilizer remains a common practice on the Canadian Prairies and a number of research studies have demonstrated that N₂O emissions during spring thaw are greater from soils that received fall-applied nitrogen fertilizer compared to soils that did not. However the magnitude of losses are highly variable, ranging from no statistically significant difference in emissions in some years to remarkably higher emissions from soils receiving fall-applied fertilizer in other years. Microbial processes drive the conversion of nitrogen to gaseous forms thereby determining the magnitude of N₂O production.

Understanding the dynamics of the microbial populations involved in these processes during the non-growing season is critical to confidently develop management strategies that will achieve the most efficient use of nitrogen fertilizers while generating the least emission of N₂O. However, quantification of N₂O emission from fall-applied nitrogen fertilizer during the non-growing season on the Canadian Prairies remains uncertain, and information about the microbial dynamics underlying production of N₂O during this time period is scarce. Furthermore, new enhanced-efficiency fertilizer products may provide a tool for reducing N₂O emissions during the non-growing season, but virtually no information exists as to the potential impact of these products on microbial dynamics.

Purpose

Understanding non-growing season nitrogen losses are an important part of the 4R nutrient strategy, where timing and form of nitrogen application are critical factors for optimizing nitrogen use. Since N₂O emissions are often a symptom of denitrification where nitrogen fertilizer is biologically converted to N₂ gas, reducing N₂Oemissions also means a costs savings through greater nitrogen retention for crop use. Greater understanding of biological processes of nitrogen loss in the non-growing season is critical to helping producers to optimize their nutrient stewardship potential.

This study will provide a clear comparison of N₂O emissions from soils with and without fall-applied fertilizer nitrogen during the entire non-growing season period and provide data to elucidate the microbial dynamics that drive the timing and magnitude of those emissions.

Objectives

The objectives of the study are to:
a) Quantify soil-emitted N₂O from soil receiving urea, dual-inhibitor urea or no N fertilizer during the non-growing season period under semi-arid conditions.
b) Elucidate the factors driving the timing and magnitude of soil-emitted N₂O during the non-growing season period under semi-arid conditions.
c) Elucidate the impact of a dual-inhibitor urea product on soil microbial nitrifier and denitrifier dynamics during the non-growing season under semi-arid conditions.