Synchrotron X-ray tomography: a step forward in the understanding of N2O emissions pathways in tropical soils

• Grant number: 23/11900-4
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: April 01, 2024
• End date: March 31, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: João Luís Nunes Carvalho
• Grantee: Thaís Nascimento Pessoa
• Host Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Ministério da Ciência, Tecnologia e Inovação (Brasil). Campinas , SP, Brazil
• Associated research grant: 21/10573-4 - Center for Carbon Research in Tropical Agriculture (CCARBON), AP.CEPID

Abstract

Soil structure controls chemical, physical, and biological processes in the soil, including nitrous oxide (N2O) emissions. Soil management practices such as integrated crop-livestock (ICL) systems interfere on soil aggregation mechanisms and pore space dynamics, mainly biopore formation, as a result of the introduction of Brachiaria species. The hypotheses of this proposal are (i) the use of Brachiaria species increases the inter- and intra-aggregate porosity of pasture and ICL systems; (ii) the crop-succession system has intra-aggregate pores with low connectivity, promoting hotspots for N2O emissions for denitrification pathways by favoring sites of water accumulation; (iii) the increase in resolution and the identification of smaller pores within the aggregates provide information on the spatial heterogeneity of the microscale and are therefore expected to provide different information about the possible hotspots of N2O emissions. Therefore, the main objectives of this purpose are to (i) quantify soil N2O emissions in a controlled environment using 15N-labelled fertilizer to quantify the N2O emission pathways (nitrification or denitrification); (ii) decipher how soil pore space parameters (e.g., porosity, pore size distribution, connectivity, and tortuosity) and soil physical-hydric properties influence N2O emissions, assessed by traditional techniques and Synchrotron radiation-based in XCT (SRXCT); and (iii) identify correlations between N2O emissions and soil pore space parameters. To achieve the objectives presented in this proposal, the Work Plan will be carried out in two phases. The first phase will include field sampling in experimental plots to better understand the influence of management and land use on soil physical-hydric properties. The second phase of the plan will be related to an incubation experiment to verify the behavior of N2O emissions and high-resolution computed tomography (SRXCT) experiments in the Mogno beamline of Sirius (LNLS/CNPEM). The experimental sites are located at EMBRAPA Agrossilvipastoril, in Sinop, State of Mato Grosso, Brazil. The experiment has been conducted to 12 years, under a Typic Hapludox, with clay texture. The results of this proposal will elucidate the dominant mechanisms of N2O emissions in tropical soils under no-tillage, ICL system, and pasture. The proposal brings a novelty in the study of the interface of soil structure of tropical soils, the application of high-resolution computed tomography (SRXCT) using a fourth-generation synchrotron source, and the use of stable isotopes from 15N-labelled fertilizers to quantify the contribution of nitrification and denitrification pathways. The combination of traditional and advanced techniques will improve the study of N2O emissions, a dynamic process that occurs in soils and is highly influenced by soil structure and will contribute to elucidate the dominant mechanisms of N2O emissions in tropical soils under different land use conditions.