Influence of soil moisture on codenitrification fluxes from a urea-affected pasture soil

Timothy J Clough,Gary J Lanigan,Sergio E Morales,Jim Grant,Lars R Bakken,Leo M Condron,Karl G Richards,Md Sainur Samad,Cecile A M De Klein,Charlotte Johns,David Rex

doi:10.1038/s41598-017-02278-y

Abstract

Intensively managed agricultural pastures contribute to N2O and N2 fluxes resulting in detrimental environmental outcomes and poor N use efficiency, respectively. Besides nitrification, nitrifier-denitrification and heterotrophic denitrification, alternative pathways such as codenitrification also contribute to emissions under ruminant urine-affected soil. However, information on codenitrification is sparse. The objectives of this experiment were to assess the effects of soil moisture and soil inorganic-N dynamics on the relative contributions of codenitrification and denitrification (heterotrophic denitrification) to the N2O and N2 fluxes under a simulated ruminant urine event. Repacked soil cores were treated with 15N enriched urea and maintained at near saturation (−1 kPa) or field capacity (−10 kPa). Soil inorganic-N, pH, dissolved organic carbon, N2O and N2 fluxes were measured over 63 days. Fluxes of N2, attributable to codenitrification, were at a maximum when soil nitrite (NO2−) concentrations were elevated. Cumulative codenitrification was higher (P = 0.043) at −1 kPa. However, the ratio of codenitrification to denitrification did not differ significantly with soil moisture, 25.5 ± 15.8 and 12.9 ± 4.8% (stdev) at −1 and −10 kPa, respectively. Elevated soil NO2− concentrations are shown to contribute to codenitrification, particularly at −1 kPa.

Highlights

Managed agricultural pastures contribute to N2O and N2 fluxes resulting in detrimental environmental outcomes and poor N use efficiency, respectively
There was a significant interaction of soil moisture and sampling date (p < 0.001) on soil pH, dissolved organic carbon (DOC) and inorganic N contents (Figs 2–4)
Soil pH in the non-urea treatment was generally constant over time (Fig. 2) regardless of soil moisture treatment, averaging 5.49 ± 0.11 (Stdev)

Summary

Introduction

Managed agricultural pastures contribute to N2O and N2 fluxes resulting in detrimental environmental outcomes and poor N use efficiency, respectively. Nitrifierdenitrification and heterotrophic denitrification, alternative pathways such as codenitrification contribute to emissions under ruminant urine-affected soil. The resulting gas products formed, N2O or N2, contain one N atom originating from the inorganic-N (e.g. NO2−), and a second atom from the co-metabolised organic compound[16,18]. Significant rates of both partial and complete codenitrification are only likely to occur if nucleophile concentrations are at least one or two orders of magnitude greater than that of NO2− and NO16

Objectives

Methods

Results

Conclusion