Agriculture is the second largest source of greenhouse gas emissions in Brazil.  The sector is second only to land-use change.  But did you know that an innovation promises to reduce this problem: the use of cashew bagasse biochar!

The replacement of conventional fertilizers with cashew bagasse biochar has been the subject of research at the Agricultural Sciences Center of the Federal University of Ceará (UFC).

Therefore, cashew bagasse, a waste product from the northeastern agribusiness, is another opportunity to reduce carbon emissions and make agriculture more sustainable.

We invited Dr.  Mirian Cristina Gomes Costa, professor at UFC and one of the authors of works on the subject, to talk about cashew bagasse biochar and its many possibilities.

What is biochar?

 Biochar is a solid material derived from the thermochemical conversion of various biomasses in an environment with limited oxygen concentration.

It can be produced from sugar cane bagasse or rice straw.   Its porous and carbon-rich structure acts as a “sponge” for water and nutrients that can help restore degraded land.

For production, biochar must be obtained under carbonization conditions in the absence or limitation of oxygen.

This means that they must be produced in closed reactors suitable for this purpose.  The pyrolysis temperature for obtaining biochars can vary from 300 to 1200 ºC, depending on the type of biomass used for production.

“This is a material that has potential for use in several sectors, including agriculture, with the aim of improving the physical, chemical and biological properties of the soil,” says Mirian Costa.  

In addition, to achieve greater economic viability of the agricultural use of biochar, the professor points out that it is important that it is produced from locally generated organic waste, such as cashew, in the northeast region.

“In the research we started in the state of Ceará, as the agroindustry associated with cashew cultivation is relevant, there is significant waste production in the sector, conferring one of the potentials for the production of biochar,” he says.

Biochar properties of cashew bagasse

In addition to using industrial waste that benefits cashew, biochar produced from cashew bagasse has physical and chemical properties that positively influence soil attributes. 

As examples of these properties, the UFC professor highlights some of the most interesting attributes: 

  • Porosity; 
  • Presence of functional chemical groups; 
  • The presence of chemical elements considered nutrients for plants, such as phosphorus, potassium, calcium and magnesium.° 

The CFU study also showed that the application of doses ranging from 10 to 40 Mg/ha of cashew bagasse biochar improved soil porosity and promoted silica adsorption.

It thus reduced the expression of cohesion, which was translated into a decrease in soil density and mechanical resistance to plant root growth.

“These properties help alleviate the physical limitations of dense soils, increase water availability, and provide some of the nutritional needs of crops, reducing the need for mineral fertilizers,” adds Mirian.  

Another characteristic of biochar cited by the researcher is its ability to contain a greater amount of carbon in a more stable form, so that its agronomic application contributes to carbon sequestration in the soil. 

“With this carbon “stored” in the soil and in a more stable form, it is not easily emitted into the atmosphere in the form of CO2,” he points out.

Tests helped identify applications for cashew biochar

Although it is a promising idea, the UFC professor emphasizes that there are scientific doubts about how long these biochars will benefit the properties of the soil. 

For this reason, the researchers conducted several tests on the use of cashew bagasse biochar: 

  • To reduce the cohesion of soils with a cohesive character, whose occurrence is significant in the Coastal Tabuleiros zone where there is agricultural production of socio-economic importance;
  • To improve the physical, chemical and biological characteristics of degraded soils of a desertification core. “This can improve the conditions for agricultural crops in local communities, as well as promote actions to recover degraded areas,” adds Mirian:  
  • Recovery of soils affected by salts, whose occurrence is common in the Brazilian semi-arid context, but which can also be found in agricultural production areas in other climatic contexts of the country. 
  • Fertilizer formulation.  “We found that its use reduced by half the mineral fertilizers required for corn cultivation.”

In addition to agronomic applications, cashew bagasse offer many other possibilities, such as:

  • Natural dye;
  • Animal feed; 
  • Pharmaceutical ingredients;
  • Hydrogen production;
  • Energy production;
  • Production of bioplastics, among others.

Challenges and Prospects for the Use of Cashew Bagasse Biochar

The work is still ongoing and aims to answer a number of questions about the efficiency of using cashew biochar in agriculture.

But according to the UFC professor, there are still challenges to overcome.  There are still many steps to be taken.

“The positive results we have observed so far have been obtained in studies conducted in greenhouses, that is, under controlled conditions.”  

Therefore, the next steps are to conduct field studies to more fully monitor the effects of biochar on soils and plants over different cycles until a stage is reached where crop productivity can be assessed. 

Given the evolution of technology, it is natural for progress to occur.  These steps are called “technology readiness levels,” or TRLs. 

“We have reached TRL 4, where the functionalities of cashew bagasse biochar were found in a controlled environment.  Now our challenge is to move to TRL 5 through field experiments,” adds Mirian.  

To this end, we have the following challenges: 

  • Obtain funding for research; 
  • Have the structure to produce cashew bagasse biochar in sufficient quantities for field studies; 
  • Obtain coefficients that indicate the economic viability of the technology for effective implementation.

But if the answers are positive, the conditions will have been created to significantly change the reality of the region through a cashew crop residue.