Archive for the category: Nitrous oxide emissions from agriculture

Rui Liu¹, Helen Suter¹, Helen L Hayden², Jizheng He¹, Deli Chen¹

¹ Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Victoria 3010, Australia

² Department of Economic Development, Jobs, Transport and Resources, Bundoora, Victoria 3083, Australia

Abstract

The continuous increase of the greenhouse gas nitrous oxide (N₂O) in the atmosphere due to increasing anthropogenic nitrogen input in agriculture has become a global concern. In recent years, identification of the microbial sources responsible for soil N₂O production has substantially advanced with the development of isotope enrichment techniques and the discovery of specific nitrogen-cycling functional genes. However, little information is available to effectively quantify the N₂O produced from different microbial pathways (i.e. nitrification and denitrification). ¹⁵N-tracing incubation experiments were conducted, using soil from different land-uses, under controlled laboratory conditions to quantify nitrification-sourced N₂O production. Nitrification was found to be the main contributor to N₂O production, contributing to 96.7% of the N₂O emissions in the sugarcane soil followed by 70.9% in the cereal cropping soil and 70.9% in the dairy pasture soil, while only around 20.0% of N₂O was produced from nitrification in vegetable soil. The greatest contribution from nitrification was observed at 50% and 70% WFPS regardless of soil temperature. At 50%, 70% and 85% WFPS, nitrification contributed 87%, 80% and 53% of total N₂O production, respectively at 25°C, and 86%, 74% and 33% of total N₂O production, respectively at 35°C. These findings can be used to develop better models for simulating N₂O from nitrification to inform soil management practices for improved N use efficiency.

Lynne Macdonald¹, Mark Farrell¹ and Jeff Baldock¹

¹ CSIRO Agriculture, PMB2, Glen Osmond, SA 5064, Australia (lynne.macdonald@csiro.au)

Abstract

The carbon (C) and nitrogen (N) cycles in soil are intrinsically linked.  Recently, and with particular reference to increased awareness of climatic change, there has been focus on increasing sequestration of C in agricultural soils as a potential greenhouse gas mitigation strategy.  However, increased C content in soils often also leads to an increased rate of both C and N cycling.  In the context of C accounting and defining the net greenhouse gas benefits of sequestering atmospheric CO₂-C in soil, it is important to understand the potential implications of building soil C on the flux of N₂O generated by N cycling processes (Zaehle et al. 2011).

Louise Barton¹, Daniel V. Murphy², Klaus Butterbach-Bahl³

¹ Soil Biology and Molecular Ecology Group, School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia, louise.barton@uwa.edu.au

² Soil Biology and Molecular Ecology Group, School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia, daniel.murphy@uwa.edu.au

³ Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research Atmospheric Environmental Research (IMK-IFU), 19 Kreuzeckbahnstr., Garmisch-Partenkirchen, 82467, Germany, klaus.butterbach-bahl@kit.edu

Abstract

Understanding nitrous oxide (N₂O) fluxes from agricultural soils in semi-arid regions is required to better understand global terrestrial N₂O losses. Nitrous oxide fluxes were measured from three rain-fed, cropped soils in a semi-arid region of south-western Australia on a sub-daily basis from 1995 to 2014 using automated chambers. Western Australia’s grain-belt includes 7 million hectares of arable land, with cropping confined to winter and soils fallow at other times. Nitrogen fertilizer (up to 100 kg N ha^-1 yr^-1) was applied at planting and during the growing season depending on crop requirements. In situ N₂O measurements were consistently small from all sites (0.04–0.27 kg N ha^-1 yr^-1), representing 0.01 to 0.12% of applied N fertilizer. Increasing soil organic matter (OM) increased soil N₂O fluxes, but losses represented <0.12% of the N fertilizer applied. While including grain legumes in cropping rotations also did not enhance soil N₂O fluxes in the growing season or post-harvest. Developing strategies for mitigating N₂O fluxes from cropping soils in our region is challenging as most losses occur post-harvest, when there is no active plant growth, and in response to summer rainfall. Increasing the efficiency of the nitrification process by increasing soil pH (via liming) decreased N₂O fluxes from sandy, acidic soils following summer rainfall, and is a potential strategy for mitigating N₂O fluxes from nitrification. Accurately accounting for N₂O fluxes in our region has refined Australia’s national greenhouse gas inventory and demonstrated annual fluxes can be low from cropped soils in semi-arid regions.