Amazon dark earth boosts tree growth as much as sixfold

Newswise — According to a study published in the journal Frontiers in Soil Science, a type of soil known as Amazon dark earth (ADE) or terra preta da Amazônia, can accelerate tree growth and improve their overall quality of development.

The findings reported in the article resulted from studies supported by FAPESP (projects 20/08927-0, 18/19000-4 and 14/50320-4) under the aegis of its Biodiversity, Characterization, Conservation, Restoration and Sustainable Use Program (BIOTA). 

“ADE is rich in nutrients and supports communities of microorganisms that help plants grow, among other things. Native people of the Amazon have used ADE to grow food for centuries and don’t need fertilizer for plants,” said Luís Felipe Guandalin Zagatto, a master’s student at the University of São Paulo’s Center for Nuclear Energy in Agriculture (CENA-USP) in Piracicaba, Brazil, and one of the authors of the article.

The researchers discovered that the microbiota present in Amazon dark earth (ADE), including bacteria, archaea, fungi, and other microorganisms, significantly benefits plant growth. When ADE was added to the soil, it greatly enhanced the growth of three tree species examined in the study. Seedlings of Brazilian cedarwood and Yellow poinciana grew between two to five times taller than normal when 20% ADE was added to the soil, and three to six times taller with 100% ADE, compared to growth in the control soil without ADE. Ambay pumpwood did not grow at all in the control soil but thrived when grown in 100% ADE. This indicates that ADE has a remarkable positive effect on the growth and development of these tree species.

In the presence of Amazon dark earth (ADE), the dry mass of Brachiaria forage grass experienced significant growth. When the soil contained 20% ADE, the dry mass increased more than threefold compared to the control soil. Moreover, with 100% ADE in the soil, the dry mass of Brachiaria forage grass increased by more than eight times. This demonstrates the remarkable positive impact of ADE on the growth of the forage grass.

According to Anderson Santos de Freitas, the first author of the article and a PhD candidate at CENA-USP, the bacteria present in ADE play a crucial role in plant growth. They act like miniature "chefs" by converting certain molecules in the soil into substances that can be readily absorbed by plants. To simplify, these bacteria transform substances that plants wouldn't be able to utilize directly into ones that are beneficial for their growth and metabolism.

Amazon dark earth (ADE) was found to be significantly richer in nutrients compared to the control soil. For instance, ADE contained 30 times more phosphorus and three to five times more of each of the other measured nutrients, except for manganese. Additionally, ADE exhibited a higher pH level than the control soil. This abundance of nutrients and higher pH likely contributes to the enhanced plant growth observed in the presence of ADE.

Zagatto and his colleagues collected samples of Amazon dark earth (ADE) from the Caldeirão Experimental Field in Amazonas state. On the other hand, the control soil was obtained from experimental croplands maintained by Luiz de Queiroz College of Agriculture (ESALQ-USP) in Piracicaba, São Paulo state. These two different soil sources allowed the researchers to conduct a comparative analysis of the effects of ADE on plant growth and nutrient content.

In their experiment, the researchers filled a total of 36 four-liter pots, with each pot containing 3 kg of soil. These pots were then placed in a greenhouse where the average temperature was maintained at 34°C. This temperature was chosen to simulate the potential impact of global warming on the Amazon region, as the current temperatures there range from 22°C to 28°C. By using this controlled environment, the researchers could study the effects of higher temperatures on the growth of plants in both the ADE and control soil conditions.

A third of the pots were filled with control soil, a third with a 4:1 mixture of control soil and ADE, and a third with 100% ADE. To mimic pasture, they planted seeds of Brachiaria forage grass (Urochloa brizantha) in every pot, leaving them to sprout for 60 days. They then cut the grass but left the roots, simulating restoration of degraded pasture by sowing seeds of the three tree species. 

Biotech applications

Zagatto clarified that their research group does not advocate for the direct use of Amazon dark earth (ADE) due to its limited availability and protected status. Instead, the main objective of their study is to analyze the chemical properties of ADE, such as its nutrient content, organic matter, and pH levels. They also investigated enzyme activity and other biological and biochemical aspects that contribute to the beneficial effects on plant growth. By understanding these characteristics of ADE, the researchers aim to gain insights into how to optimize soil conditions for improved plant development and agriculture practices.

Zagatto emphasized the importance of identifying the specific microorganisms responsible for the positive effects observed in ADE. The ultimate goal is to harness these microorganisms' benefits without relying on the finite ADE resource directly. To achieve this, the researchers aim to explore biotechnological developments that can replicate the characteristics exhibited by ADE. Understanding the mechanisms involved and finding ways to apply them in a controlled and sustainable manner could lead to innovative agricultural practices. This study represents an initial stride towards that objective.

Deforestation is a significant issue in Brazil, affecting not only the Amazon but also other regions. The reasons for deforestation vary, including the conversion of forests into pasture or croplands. There is a growing urgency to find effective methods to restore these areas quickly to allow the regrowth of forests and the resumption of essential ecosystem services. These services provide numerous benefits to the environment and human populations, such as regulating climate and air quality and storing carbon in the soil. Finding sustainable ways to restore these areas is crucial for safeguarding the environment and promoting the well-being of communities.

Zagatto stated that their study aimed to identify a potential catalyst for enhancing ecological restoration projects in tropical forests, particularly in the Amazon. The ultimate goal is to help these areas recover as close as possible to their original state. The promising results from their research indicate that incorporating the beneficial characteristics of Amazon dark earth (ADE) into seedling production or directly into the restoration sites could expedite the process of ecological restoration for tropical forests. By leveraging the properties of ADE, it might be possible to accelerate the recovery of these vital ecosystems, contributing to their preservation and promoting overall ecological well-being.

About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.