Contribution of crop residue, soil, and fertilizer nitrogen to nitrous oxide emissions varies with long-term crop rotation and tillage

Pedro Vitor Ferrari Machado; Richard E Farrell; William Deen; R Paul Voroney; Katelyn A Congreves; Claudia Wagner-Riddle

doi:10.1016/j.scitotenv.2021.145107

Contribution of crop residue, soil, and fertilizer nitrogen to nitrous oxide emissions varies with long-term crop rotation and tillage

Sci Total Environ. 2021 May 1:767:145107. doi: 10.1016/j.scitotenv.2021.145107. Epub 2021 Jan 28.

Authors

Pedro Vitor Ferrari Machado¹, Richard E Farrell², William Deen³, R Paul Voroney⁴, Katelyn A Congreves⁵, Claudia Wagner-Riddle⁴

Affiliations

¹ School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, ON N1G2W1, Canada. Electronic address: pferrari@uoguelph.ca.
² Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada.
³ Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G2W1, Canada.
⁴ School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, ON N1G2W1, Canada.
⁵ Department of Plant Sciences, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada.

PMID: 33550054
DOI: 10.1016/j.scitotenv.2021.145107

Abstract

Agriculture is an important contributor to N₂O emissions - a potent greenhouse gas - with high peaks occurring when soil mineral nitrogen (N) is high (e.g., after mineralization of organic N and N fertilizer application). Nitrogen dynamics in soil and consequently N₂O emissions are affected by crop and soil management practices (e.g., crop rotation and tillage), an effect mostly assessed in the literature through comparisons of total N₂O emission. Hence, information is scarce on the effect of these management practices on specific N sources affecting N₂O emissions (i.e., N fertilizer, soil, above and belowground crop residues) - a knowledge gap explored in this study with the use of ¹⁵N tracers. The isotope approach enabled refinement on global N₂O budget by directly determining the emission factors (EF) of above and belowground crop residues that vary in chemical composition and comparison with default EF values (e.g., IPCC EFs). Our experiment was conducted over the full-cycle of long-term crop rotations to (i) compare N₂O totals and intensity, under no-tillage and conventional tillage, simple and diverse rotation; (ii) partition total N₂O emissions into soil, N fertilizer, above and belowground crop residue N sources; (iii) compare the 12-month EF of crop residue against the default values proposed by IPCC (2019). For the tillage effect, annual N₂O emissions were from 1.2- to 2.0-times higher on CT than NT soil due to 40% increased soil N derived N₂O emission in CT. The diversified crop rotation emitted 1.3-times higher N₂O than the simple rotation over the full-cycle of the rotations, but the effect was due to differences in N fertilizer rate between the rotations since emissions were equivalent when scaled by N rate. Finally, our results suggested that default IPCC EF are overestimated for crop residues under CT and NT, simple and diverse rotations as measured EFs never surpassed 0.1%.

Keywords: (15)N(2)O; Chamber measurements; Cover crop; Emission factors; N(2)O; Nitrogen isotope tracer.