Does brazilian agriculture benefit from fires?

Between August and September 2024, a catastrophic fire scenario took hold in Brazil. Caused by extreme weather events, such as reduced rainfall, high temperatures and strong winds, the fires spread across all Brazilian biomes, especially in the Amazon and Cerrado, affecting forest and crop areas.

According to the National Institute for Space Research (INPE), 2024 was one of the years with the highest number of fire outbreaks recorded in the last decade. Compared to 2023, in August, there was a jump from around 28 thousand outbreaks to more than 68 thousand outbreaks in the national territory in 2024, reaching around 5,65 million hectares, the equivalent of the entire state of Paraíba. The environmental and financial losses resulting from these events are difficult to measure.

Fire is an ecological disturbance with a major impact on soils. Some of the main negative effects on soil resulting from fires are the loss of organic matter, deterioration of soil structure and disruption of essential microbial communities. These factors can directly affect the productivity of commercial agricultural crops.

Fires can alter soil biogeochemical cycles, affecting the availability of nutrients and the distribution of fauna living within the soil, and can also affect properties such as soil particle aggregation, soil stability and permeability. These effects are caused by combustion activity that occurs mainly in the surface fractions of the soil, where the average temperature can reach between 200 and 300 °C and can increase to 500–850 °C, due to the presence of vegetation with highly flammable combustible properties.

The high temperatures generated by burning on the soil surface can spread to deeper layers of the soil, potentially breaking the biological stability thresholds of most life forms in the soil: this means that seeds, plant tissue, nutrients and microorganisms essential for plant development could be compromised, affecting the biological and productive activity of the soil. To illustrate the impact of burning, one hectare of cropland contains around 2 million kilos of soil, of which 80 thousand kilos are organic matter (4% of the soil composition), including 1,2 thousand kilos of nitrogen. With burning, this nitrogen is completely lost, requiring R$4,5 thousand in 1,8 thousand kilos of urea to replace it. Furthermore, it can take decades to recover the 4% level of organic matter in the soil. For every 1% increase in organic matter, 10 tons of straw per hectare are needed over 10 years, and it can take around 40 years to reach the target.

Figure 1 - Soil profile and heat distribution throughout its depth

Source: Own elaboration

In addition to the immediate effects caused by fires, it is necessary to consider that the burning of the soil's vegetation cover results in an increase in the uncovered area of ​​soil, favoring the effects of absorption of solar radiation as well as erosion processes, which imply the loss of soil through the action of wind and the impact of raindrops.

Although the practice of burning in agriculture has been used for millennia by indigenous and rural communities to increase soil fertility in the short term by releasing nutrients from burned vegetation, repeated or excessive use can lead to soil degradation in the long term. Over time, technological progress has introduced new methods that eliminate any need for fire, making the technique less and less used and considered outdated. In this scenario, the use of fertilizers, mulching the soil with straw and incorporation of organic matter into the soil reduce the need for burning, but the technique continues to be used. However, unlike catastrophic events, there is regulation and management control required in the event that burning is still carried out.

The National Fire Management Policy became a law in 2024 (Law 14.944, of 2024), establishing guidelines for the use of fire in rural areas and distinguishing controlled burns from prescribed burns and uncontrolled burns. According to the law, controlled burns refer to the planned use of fire for agricultural purposes, with required authorization and following a management plan to avoid environmental damage. Prescribed burns are similar, but aim at environmental conservation, research or vegetation management, also requiring authorization and planning. Uncontrolled burns occur in a disorderly and unauthorized manner, usually illegal, causing great environmental damage, such as loss of biodiversity, destruction of vegetation and increased CO2 emissions. According to the Amazon Environmental Research Institute (IPAM), it is estimated that the fires that occurred in the Amazon biome between July and August 2024 alone emitted around 31,5 million tons of CO2 equivalent.

In general terms, it is assumed that the fires between August and September 2024 were uncontrolled, with an uncertain and perhaps even criminal origin, aggravated by the dry weather conditions that plagued Brazil during this period. As a consequence, last year's fires resulted in major economic losses in terms of agricultural productivity. According to the Brazilian Confederation of Agriculture and Livestock (CNA), approximately 2,8 million hectares of rural properties were affected by the fires, with losses estimated at approximately R$14,7 billion. Among the losses, the greatest were in pasture and livestock areas, including only beef cattle production (R$8.106.052,30), sugarcane (R$2.762.773,72), other crops of economic interest (R$1.068.357,61), and rural infrastructure, such as fences (R$2.824.929,13). The states most affected by the losses caused by the fires were São Paulo, with R$2,8 billion in losses, followed by Mato Grosso, with R$2,3 billion, Pará, with R$2,0 billion, and Mato Grosso do Sul, which recorded losses of R$1,4 billion.

Figure 2 - Number of fire outbreaks recorded in August 2024 by Brazilian State

Source: INPE

According to INPE, up until November 2024, 248.203 fire outbreaks were recorded in Brazil, the highest number since 2010. This is also the second highest rate since the historical record of 393.915 outbreaks, recorded in 2007. These data show a worrying increase in fires, placing 2024 among the most critical years in the historical series and reinforcing the need for measures to combat and prevent forest fires in the country.

In view of the enormous financial and environmental losses, the Federal Government recently published Decree No. 12.189, of September 20, 2024, making penalties for forest fires in Brazil more severe. The decree establishes new fines and intensifies existing penalties, as a strategy to minimize burning practices. In addition, the enactment of Law 14.944 of 2024, modifying the Forest Code (Law 12.651, of 2012) and the Environmental Crimes Law (Law 9.605, of 1998), provides for the gradual replacement of burning by alternative techniques, especially in indigenous and more traditional communities, which still use burning as a management technique.

Therefore, answering the question in the title of this study, burning has no longer been of interest to agricultural production for years, as more appropriate and productive management practices exist and are widely used.

References and Recommended Reading

AMURAT, N. et al. Fire impacts on soil properties and implications for sustainability in rotational shifting cultivation: a review. MDPI Agriculture, vol. 14, no. 9, p. 1660, 2024.

BRAZIL. Law No. 14.944, of July 31, 2024. Establishes the National Policy for Combating Forest Fires and Environmental Crimes. Official Gazette of the Union, Brasília, July 31, 2024. Accessed on: November 01, 2024.

BRAZIL. Decree No. 12.189 of 2024. Amends Decree No. 6.514 of July 22, 2008, which provides for administrative offenses and sanctions related to the environment. Accessed on: November 01, 2024.

BRAZIL. Law No. 9.605, of February 12, 1998. Provides for criminal and administrative sanctions arising from conduct and activities harmful to the environment and provides other measures. Accessed on: November 01, 2024.

Brazilian Confederation of Agriculture and Livestock (CNA). Recommendation to rural producers impacted by fires. Accessed on: October 29, 2024.

Fires can cause irreparable damage to the soil. Compre Rural, 2024. Accessed on: October 29, 2024.

Wildfires cause over R$14 billion in damage to the countryside. G1 Globo, September 26, 2024. Accessed October 29, 2024.

NATIONAL INSTITUTE FOR SPACE RESEARCH (INPE). Terra Brasilis: monitoring of active fire outbreaks by country. Accessed on: November 01, 2024.

Amazon Environmental Research Institute (IPAM). CO₂ emissions from fires in the Amazon increase by 60% . Accessed on: December 12, 2024.

KLINK, CA et al. The role of vegetation on the dynamics of water and fire in the Cerrado ecosystems: implications for management and conservation. MDPI Plants, vol. 9, no. 12, p. 1803, 2020.

MAPBIOMAS. Data from MapBiomas shows that the area affected by fire was 119% larger than the same period in 2023. July 12, 2024. Accessed October 29, 2024.

SALIM, ISH et al. Fire shifts the soil fertility and the vegetation composition in a natural high-altitude grassland in Brazil. Environmental Challenges, vol. 9, p. 100638, 2022. Accessed on: 29 Oct. 2024.

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