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Maurício Roberto Cherubin

Professor at the Department of Soil Science at Esalq/USP

OpAA74

Agave in the soils of the Brazilian sertão: synergy between energy and carbon sequestration

Co-authors: Tiago Osório Ferreira and Carlos Eduardo Pellegrino Cerri, Professors at the Soil Science Dept at Esalq/USP

Approximately one third of the rural population in developing countries lives in arid and semi-arid regions, facing recurrent water shortages and food insecurity. In addition, these regions are the most vulnerable to current and future climate change scenarios . In Brazil, the semiarid region covers 12% of the national territory (900,000 square kilometers) and is home to about 28 million people, encompassing the nine states of the Northeast region and the northern part of the state of Minas Gerais.

The characteristic climate regime, marked by scarce rainfall (less than 800 millimeters), high evapotranspiration rates (up to 2500 millimeters per year) and long periods of drought, is one of the greatest challenges for the sustainability of agriculture and the maintenance of natural ecosystems. Of region. Recent studies point to an intensification of processes, such as desertification in the last decade, mainly in pasture areas and in the caatinga biome, thus impacting natural and agricultural ecosystems. In this context of degradation, combating the loss and depletion of semi-arid soils emerges as one of the greatest challenges of science for a future marked by a scenario of climate change.

Soil constitutes the largest reservoir of terrestrial carbon and, therefore, is a key element in the fight against desertification, climate change and the promotion of food security. It is estimated that the amount of carbon stored in soils up to one meter deep is around 1,550 petagrams of carbon, which represents about three times the amount of carbon present in the biosphere (vegetation and animals) and twice the amount contained in the Earth's atmosphere. In the first 30 centimeters alone, they store almost the same amount of carbon (800 petagrams of carbon) stored in the atmospheric compartment. Therefore, production systems based on management practices that favor the capture of atmospheric carbon by plants and the increase of soil carbon stocks contribute significantly to the reduction of carbon concentrations in the atmosphere and, consequently, to the attenuation of the greenhouse effect and the changes global climates.

In this context, soil is a fundamental component within the Brazilian Program for the development of Agave. Despite the enormous size of the Brazilian semi-arid region, the project, in a first phase, will focus its activities in the hinterland of Bahia, a region known as “Território do Sisal”. This region is marked by typical soils (representative) of the Brazilian semiarid region, with a predominance of Planosols , Neosols ( Litholic and Regolitic ), Luvissols and Vertisols , as shown in Figure 1.

Planosols are characterized by expressive increases in clay in depth and, therefore, by the presence of a marked textural gradient in depth. They are soils with severe limitations from the physical-hydric point of view, especially in relation to drainage and infiltration of water and, commonly chemical, such as the presence of salts.

The subsurface horizons, characterized by high density and low hydraulic conductivity, favor bad drainage events during the rainy season, as well as the lack of aeration for the plant root system and erosion.

The Neosols Litholics and Regoliths are, in turn, marked by the low effective depth and the presence of rock contact within the first 50 centimeters of soil (for example: Neosols litholic), or just below (e.g. Neosols regoliths).

They are soils marked by the presence of gravel, occasionally associated with rock outcrops (Figure 2) and which often present stony and rocky terrain. In some cases, they are associated with conditions of busier relief, with steep slopes. In the sisal region, the soils of this order are associated with different types of rocks, especially with lands marked by the presence of granitic and gneissic rocks.

The Luvissols comprise soils that present textural differentiation within the profile (surface horizon depleted in clay followed by a horizon with accumulation of clay in the subsurface ), due to the presence of clays of high activity and high chemical fertility. They are, in general, shallow soils, with low levels of organic carbon and, usually, with stoniness on the surface.



Vertisols, in turn, are clayey soils with high proportions of expansive clays and, therefore, commonly form deep cracks in dry seasons . These are soils of high natural fertility, however, with physical characteristics that make their management difficult in conditions of low- tech agriculture.

Given the characteristics of the soils present, management becomes quite complex and challenging. In the Brazilian Program for the development of Agave, management alternatives will be studied that aim to increase the sequestration and stabilization of carbon in the soil and, thus, establish production systems that result in a positive carbon balance. Therefore, one of the goals of the Brazilian Program for the development of Agave will be the establishment of management practices that will increase the production of agave biomass and the consequent amount of atmospheric carbon (carbon dioxide) captured by these plants. In parallel, intensified production systems will be studied, associating management practices that add carbon to the soils (Figure 3) in other ways, such as: 1) intercropping agave with cover crops, such as buffel grass (Cenchrus ciliares), with or without integration with livestock (goat, sheep and cattle), 2) addition of fresh organic waste, such as sisal defibration residue and manure, and 3) addition of biochar (biochar), an organic compound obtained from the pyrolysis of biomass, which can be produced from the cultivation of plants adapted to the sertão, such as pau-de-rato (Poincianella pyramidalis).

The establishment of new models of agave production in the countryside, using innovative management techniques adapted to the reality of agriculture in the northeastern hinterland, has the potential to make the agave culture a matrix for transforming the social, economic and environmental reality of a of the most extensive and unique regions of Brazil.