Terra Preta da Amazônia increases tree growth by up to six times

A soil known as Terra Preta da Amazônia (TPA) promotes better tree growth both in terms of quality and speed. The conclusion is from an article published in the magazine Frontiers in Soil Science, the result of investigations supported by FAPESP within the scope of the BIOTA Program.

“TPA is rich in nutrients and supports communities of microorganisms that, among other things, help plants grow,” explains Luís Felipe Guandalin Zagatto, master’s student at the Center for Nuclear Energy in Agriculture at the University of São Paulo (Cena-USP) and one of the authors of the article. “The natives of the Amazon have used TPA to grow food for centuries and do not need fertilizer for the plants”, informs the text.

The group of researchers observed that the microbiota – the entire set of bacteria, archaea, fungi and other microorganisms – of TPA is very beneficial for plant growth. The addition of TPA boosted the growth of the three tree species analyzed by the group: pink cedar seedlings (Cedrela fissilis) and angico-yellow (Peltophorum dubium) were 2,1 and 5,2 times higher with 20% TPA and 3,2 and 6,3 times higher with 100% TPA, compared to control soils. The embaúba (Cecropia pachystachya) did not even grow in soils without TPA (control), but thrived with 100% Terra Preta. Also, the dry mass of brachiaria grass, used in pastures, increased 3,4 times with 20% TPA and 8,1 times with 100%, compared to the control soil.

“TPA bacteria act by transforming some soil molecules into substances that can be absorbed by the plant”, details Anderson Santos de Freitas, a doctoral student at Cena who also wrote the article. “Making a very rudimentary analogy, you could say that bacteria act as 'mini-cooks', transforming substances that the plant cannot 'ingest' into things that it actually uses”, explains Freitas, who is also co-creator of the podcast Biotec em Pauta .

The TPA had higher amounts of nutrients than the control soil: for example, 30 times more phosphorus and three to five times more of each of the other nutrients measured, except manganese. It also had a higher pH.

Zagatto and his colleagues collected TPA samples at the Caldeirão Experimental Field, in the State of Amazonas, and, as a control, in agricultural soil at the Luiz de Queiroz College of Agriculture (Esalq-USP), in Piracicaba. They filled 36 four-liter pots with three kilos of soil, installed in a greenhouse with an average temperature of 34°C – in an exercise to anticipate global warming, given that current temperatures in the Amazon range between 22° and 28°C.

One third of the pots received only control soil, another third a four-to-one mixture of control soil and TPA and another third 100% TPA. To emulate pasture, they planted brachiaria grass seeds (Urochloa brizantha), common forage for livestock in Brazil, and let their seedlings grow for 60 days. Then they cut the grass and left only its roots – ideal terrain for simulating the condition of restoring degraded pastures. The researchers then replanted each of the three soils with seeds from the three tree species analyzed.

Biotechnological applications

Zagatto highlights that the group's proposal is not to use the soil itself, since TPA is a finite and highly protected resource. The objective of the research is to understand which are the chemical (such as nutrients, organic matter and pH), biochemical (such as enzyme activity) and biological characteristics of TPA that are so beneficial to plants.

“We need to understand exactly which microorganisms are responsible for these effects and how we could use them without needing the TPA itself. From then on, we will try, for example, to replicate these characteristics through biotechnological developments. This work is a first step in that direction”, he adds.

Brazil is losing many forest areas, not only in the Amazon biome, and this occurs due to several factors, such as, for example, the replacement of forests by pasture or agricultural crops. Therefore, it is increasingly necessary to find ways to restore these areas and make forests grow quickly again and offer all ecosystem services, that is, the benefits they provide to the environment and, consequently, to human populations, among others. which regulate climate and air quality, in addition to storing carbon in the soil.

“In the study we seek to evaluate a possible improvement factor for ecological restoration projects in tropical forests, more specifically in the Amazon forest, so that, in the future, these areas can return to a state as close as possible to their original conditions”, says Zagatto. “We believe that these results are promising and show that using TPA characteristics in the production of seedlings or even directly in the field can be a way to accelerate ecological restoration projects in tropical forests.”

The article Amazonian dark earths enhance the establishment of tree species in forest ecological restoration be read here.