# Wet‐dry cycles control the emissions and sources of greenhouse gases in agricultural soil: An incubation study

## TL;DR

This study shows how wet-dry cycles and nitrogen fertilization affect greenhouse gas emissions in agricultural soil.

## Contribution

The study identifies the role of wet-dry cycles and urea fertilization in controlling N2O and CO2 emissions from soil.

## Key findings

- Wet conditions (80%–55% WFPS) caused the highest N2O and CO2 emissions.
- Rewetting events temporarily increased gas emissions due to microbial activity.
- Pre-existing soil organic matter nitrogen was the main source of N2O.

## Abstract

This study examines the impact of wet‐drying cycles and nitrogen (N) fertilization on soil greenhouse gas fluxes, specifically nitrous oxide (N2O) and carbon dioxide (CO2). Nine treatments were tested, combining three soil moisture regimes (55% constant, 55%–30% cycle, and 80%–55% cycle) with three N addition rates (0, 100, and 150 kg N ha−1) using 15N‐labeled urea. Soil samples from a potato (Solanum tuberosum) field in Lethbridge, Alberta, were incubated for 28 days under controlled conditions. Wet‐drying cycles involved initially wetting the soil to the upper threshold (55% or 80% WFPS) and allowing it to dry to the lower threshold (30% or 55% WFPS), followed by rewetting to restore upper moisture levels. N2O and CO2 fluxes were measured regularly using a recirculation chamber system to quantify gas emissions and determine N2O sources. Soil moisture significantly increased N2O and CO2 production (p < 0.001), with the highest emissions under wet conditions (80%–55% WFPS cycle), moderate production at 55% WFPS, and the lowest under dry conditions (30%–55% WFPS cycle). Compared to constant 55% WFPS, N2O and CO2 production were 33% and 403% higher, respectively, under wet conditions and 28% and 3% lower under dry conditions. Rewetting events triggered temporary increases in gas emissions due to enhanced microbial activity. Urea addition caused a stronger priming effect on N2O production under wet conditions, with urea‐derived N2O more prominent in wetter soils.

Rewetting events triggered pronounced temporary increases in N2O and CO2 production.Pre‐existing soil organic matter nitrogen (SOM‐N) was the dominant source of N2O.Urea‐derived N2O disproportionally increased with wetter conditions and higher N addition.Priming effects on N2O were minimal, though priming was enhanced by increasing soil moisture.

Rewetting events triggered pronounced temporary increases in N2O and CO2 production.

Pre‐existing soil organic matter nitrogen (SOM‐N) was the dominant source of N2O.

Urea‐derived N2O disproportionally increased with wetter conditions and higher N addition.

Priming effects on N2O were minimal, though priming was enhanced by increasing soil moisture.