#EBSstories Amazonian Dark Earth for a greener planet

04-12-2020

A soil with an extraordinary high nutrient availability in a part of the Amazonian rainforest could bring clues to new ways of fertilizing soils and reducing greenhouse emissions.

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Amazonian Dark Earth (ADE; also called ‘Terra Preta de Indio’) is a soil, which is exceptionally rich in nutrients, compared to many other Amazonian or tropical soils. This soil contains large amounts of organic carbon and phosphorus and is a model for scientists who would like to reproduce its properties in other, less fertile areas. Understanding the processes within this soil could contribute to technologies that increase soil fertility and help to trap CO2 in soil, therefore abating climate change.

“ADE was made by humans centuries ago by native communities. We think that the deposition of bones, organic waste and plant residues, combined with the burning of these deposits, could be responsible for the high level of nutrients in ADE, and in particular, phosphorus”, explains Luis Colocho Hurtarte, postdoctoral researcher on beamline ID21 and part of a team doing an experiment on this soil this week at the ESRF.

In his research, he is joined by Klaus Jarosch, from the University of Bern (Switzerland) and Steffen Schweizer, from the Technical University of Munich (Germany).

 “What we try to do on ID21 is investigate where the organic carbon, which works as compost, and the phosphorus are located within the soil aggregate, to ultimately learn more about the processes within these soils”, explains Jarosch. The samples come from their partners in Brazil (A. Westphal Muniz, Embrapa Amazônia Ocidental), who have been investigating ADE in the field for over 40 years.

On ID21, the team combine Scanning X-ray Microscopy (SXM) with Nano scale Secondary Ion Mass Spectrometry (NanoSIMS) to gain new insight on the interaction of phosphorus at the microscale. SXM and NanoSIMS are techniques complementary to each other, as SXM allows the mapping at nanometer scale of phosphorus and its chemical speciation, while NanoSIMS is able to identify and quantify the carbon and phosphorus hotspots.

“Our hypothesis is that the increased bioavailability of phosphorus in ADE is mainly explained by a heterogeneous distribution and co-localization with organic matter at the microscale”, says Colocho Hurtarte, “but we will have to wait and see when we get the data”.

“Our aim is to find out how carbon and phosphorus' associations are stabilized and where they are localised in soil aggregate structures of ADE. This knowledge could then be used as a mean to abate climate change by using a land-management practice that was developed by humans centuries ago”, concludes Jarosch.

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An experiment via Zoom. The team during their beamtime session: Klaus Jarosch (top left), Luis Colocho Hurarte (top right, from the beamline), Steffen Schweizer (bottom left) and a screenshot of the experimental data. Credits: K. Jarosch.

For now, the team are facing sleepless nights, but Jarosch chuckles: “I am quite lucky that I can do the experiment remotely from my sofa, or even from my bed, unlike Luis, who will have to be present on the beamline”.

Top image: A view from above of the Amazonian rainforest.