Study using photonic technique presents unprecedented data on carbon in the soil

At a time when the eyes of the planet are focused on discussions about preserving the environment and emission of greenhouse gases, researchers from Embrapa in São Carlos (SP) make an important contribution to detecting carbon in the soil. 

The scientists concluded that Laser Induced Fluorescence Spectroscopy (LIFS) – a photonics technique –, applied in production systems such as integrated-crop-livestock-forest (ILPF), is capable of accurately evaluating , in a clean and quick way, the degree of chemical stability of the carbon retained in the soil. The concept of photonics is quite broad and considers any technique that uses or manipulates photons.

In the study, the technique made it possible to detect that the humification index (humus formation) of soil organic matter (SOM) is 36% higher in deeper soil layers in the ILPF system than in native forest areas, references considered for the search. Both the SOM stock and tree biomass increase under this integrated system and sequester more carbon, which makes the cultivation model, with different combinations, a sustainable practice and a strong ally in the decarbonization of Brazilian agriculture.

The study may help to understand the mechanisms of carbon accumulation and stabilization in tropical soils. Its results are relevant for the imminent establishment of the global market for soil carbon credits, with direct payments to rural producers for environmental services. 

A projection by WayCarbon, a consultancy focused exclusively on sustainability and climate change, together with ICC Brasil, the local arm of the International Chamber of Commerce, indicates that the country could generate between 493 million and 100 billion dollars in carbon credits by 2030 .

The theme is one of the agendas of the 26th United Nations Conference on Climate Change, COP26, which takes place until November 12 in Glasgow, Scotland.

Unprecedented application of the technique

This is the first time that the Laser Induced Fluorescence Spectroscopy (LIFS) technique has been used to detect the degree of humification of soil organic matter in integrated systems and with trenches up to one meter deep. Traditionally, the degree of humification of SOM is determined by time-consuming and costly chemical processes. Only at a later stage are the humic substances extracted from the soil analyzed using spectroscopic techniques. 

The advantage of LIFS is that there is no need to carry out chemical extractions from the soil, just prepare a tablet and measure it. The photonic technique has, therefore, stood out as an environmentally sustainable tool, because it allows the quality and stability of organic matter to be assessed more easily and quickly than conventional methods. 

The study, with long-term field experiments, involved researchers from Embrapa Instrumentação (SP) and Embrapa Pecuária Sudeste (SP), as well as post-doctoral student in chemistry Amanda Maria Tadini, a fellow at the Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp), which observed the humification index of soil organic matter in ILPF to be 36% higher than that under native forests.  

Systems influence MOS stocks 

Soil organic matter is made up of plant and animal residues containing carbon in their structure. On the surface or embedded in the soil, SOM has several stages of decomposition. The last and most stable is humus, capable of improving the physical, chemical and biological conditions of the soil, in addition to providing nutrients and improving its productive potential. 

Due to all its attributes, whether nutrient cycling, water retention or thermal control, SOM is considered an important indicator of soil fertility and plays a fundamental role in the sustainability of agricultural systems. Thus, the different management practices adopted in agriculture directly influence carbon stocks, which can be reduced, maintained or increased in relation to native vegetation.

For Tadini, who was supervised by Embrapa Instrumentation researcher Ladislau Martin Neto (photo above), knowing the chemical and molecular composition of SOM and the carbon present in its structure can enable the improvement of more sustainable agricultural techniques with less impact on the properties of the ground. 

“Studies that evaluate the structural characteristics of organic matter are also fundamental to understanding the cycling of nutrients and their deposition in the soil”, says the doctor with a double degree in Analytical and Inorganic Chemistry from the University of São Paulo (USP) and the University of Toulon (France).

In 2019, Tadini also completed a one-year postdoctoral fellowship at Old Dominion University, Norfolk, Virginia (USA), where he gained experience in several advanced analytical techniques to assist in the detailed characterization of MOS in embedded systems.

Impact on low-carbon agriculture

The research, carried out with financial support from Fapesp, aimed to analyze the SOM humification index in different systems. 

In the field experiment, Amanda Tadini evaluated the degree of humification of crop-livestock-forest integration (ILPF), crop-livestock integration (ILP), livestock-forest integration (IPF), in addition to comparing the results with reference areas, intensive pasture, extensive pasture and native forest (NF).

The study hypothesized that soil organic matter was preserving a greater amount of stable chemical forms - longer lifetime in the soil - such as aromatic chains that lead to the stabilization of carbon and its accumulation in deeper layers, between 40 and 100 cm, in integrated production systems than in native vegetation areas. One of the study's conclusions confirmed this initial hypothesis.

“We then used LIFS and found that this spectroscopy is an effective technique for evaluating the SOM humification index in practically intact samples under different agricultural systems. In all of them, SOM humification was greater in deeper layers when compared to the native forest”, observed the researcher. 

Physicist Ladislau Martin Neto says that the ILPF system, with different combinations, stands out especially in low-carbon agriculture in Brazil since the soil under this model can sequester more carbon in the form of SOM.

“These systems are an essential carbon sink, assisting in mitigation strategies to reduce the emission of Greenhouse Gases (GHGs)”, says the researcher, former president of the International Society of Humic Substances (IHSS, its acronym in English).

Martin Neto also says that in tropical regions, for example, the chemical characteristics of SOM under soil conservation management, such as direct planting and ILPF, are still rarely evaluated in more detail.

Tropical Soil Challenges

The study also made it possible to identify, in an unprecedented way, a positive correlation between the degree of humification of soil organic matter, detected by LIFS, and the cation exchange capacity of soils (an important indicator of soil fertility) of all integrated systems, confirming the improvement in the chemical stability of organic matter compounds at greater depths.

“Understanding the behavior of SOM in these agricultural soils, predominantly Brazilian, can represent an essential tool for better understanding the dynamics of soil carbon”, says Martin Neto. According to him, in tropical regions, the dynamics of soil organic matter and the importance of reactivity are magnified and result in some specific challenges. 

In turn, Embrapa Pecuária Sudeste researcher José Pezzopane states that agricultural areas such as integrated systems present a relevant annual biomass production, with significantly greater amounts of residue above and below ground than a native forest. “We observed this, especially, in areas with restrictions on the chemical conditions and fertility of the original soils, in Cerrado regions or in Atlantic Forest/Cerrado transition areas, as in the case of the field experiment carried out.”

Good practices lead to carbon accumulation

Embrapa Pecuária Sudeste researcher Alberto Bernardi, a specialist in soil fertility, reinforces that the studies, after five years of implementing the ILPF system, showed very interesting results.

“Work carried out at Embrapa Pecuária Sudeste already showed that the amount of carbon was greater in soils in integrated systems. However, this study made it possible to better demonstrate the dynamics of organic matter and determine the reasons why these systems accumulate more carbon and why the chemical element remains in the soil for longer. Through sophisticated methods, the research proves higher quality and more stable organic matter, guaranteeing environmental advantages of integrated systems”, highlights Bernardi, who is also coordinator of the Crop-Livestock Integrated Systems Network of the Global Gas Research Alliance of the Greenhouse Effect in Agriculture (Global Research Alliance in English, GRA) and the Soil Fertility and Plant Nutrition Commission of the Brazilian Society of Soil Science (SBCS)

The researcher believes that the main reason for the results is the very high biomass production. “The more organic matter in the soil, the more efficient it is biologically and chemically and also physically more structured. Organic matter is the key to the proper functioning of the soil, allowing greater productivity, aquifer recharge, carbon and biodiversity”, explains Bernardi.

Furthermore, he recalls that good management practices are important, such as the application of liming and fertilizers and the adoption of direct planting, avoiding erosion processes and allowing an increase in SOM content compared, for example, with conventional tillage areas. .

Martin Neto, co-coordinator of the Farmland Research Group of the Global Alliance for Research on Greenhouse Gases in Agriculture since February 2012, also adds that the possibility of increasing the content of organic matter in the soil and, consequently, sequestering carbon is a of the important global strategies for decarbonizing the economy.

“It is also important for the establishment of the global market for soil carbon credits. At the end of September, the ton of CO2 equivalent sequestered reached values ​​around US$70,00, an increase of 90% since January of this year, according to data from the European institution Ember”, recalls the researcher.

For Alberto Bernardi, ILPF is a trend and research indicates ways for producers to sell carbon credits in the future.

The integration systems at Embrapa Pecuária Sudeste, where the studies were carried out, are maintained with support from the ILPF Network.