Proper soil management increases carbon sequestration in irrigated areas

A study conducted in Itaí, SP by scientists from Embrapa Meio Ambiente (SP) and Embrapa Solos (RJ) proved that the use of sustainable agricultural practices, such as the Direct Planting System (SPD), in irrigated areas, is capable of increasing the soil carbon stock (ECS), reducing the release of gas into the atmosphere. The conclusion is the result of comparisons and evaluations of the physical and water attributes of soil samples from two first-order basins (main water flow from the spring) cultivated with SPD under center pivot irrigation.

The study, authored by Embrapa researchers Heloisa Filizola, Alfredo Luiz, Aline Maia and Luís Carlos Hernani, was published in the Revista de Estudos Ambientais. By pointing to an increase in ECS, which is one of the key indicators for evaluating agricultural practices, the research shows that the use of SPD in the studied region directly impacts the reduction in the formation of greenhouse gases (GHGs) by retaining CO2 in the soil.

“The increase in demand for food, associated with the scarcity of areas for agricultural expansion, makes it increasingly necessary to carry out studies related to soil conservation and the reduction of atmospheric carbon,” declares Filizola. 

The areas evaluated presented a Direct Planting Participatory Quality Index (IQP) – a methodology that evaluates the quality of this production system based on a set of indicators that relate efficiency, profitability and environmental conservation – and similar physical-water conditions. In the parts where management was better carried out, there was greater water retention and around 50% less clay dispersion.

The adoption of management systems, such as Direct Planting, helps to preserve the physical quality of soils, since the diversification and intercropping of species increase the quantity and distribution of roots. Additionally, the soil surface remains covered with growing plants or crop residue, moderating evaporation and minimizing erosion losses. 

Carbon sequestration: more than just a key indicator, it is crucial for reducing GHGs

There is scientific consensus that terrestrial ecosystems are of great importance in the carbon cycle and that the soil is considered its largest reservoir. Carbon sequestration in the soil depends on factors such as vegetation cover, management practices and soil classes. 

According to Filizola, soil carbon stocks are key indicators in the provision of environmental services promoted by good agricultural practices and this is explained by the strong correlation between this element and chemical, physical and biological attributes, therefore serving as a sustainability evaluator. 

According to the Intergovernmental Panel on Climate Change (IPCC), soil stores approximately four times more carbon than plant biomass and three times more than the atmosphere, thus having great importance in the biogeochemical carbon cycle. The importance of maintaining carbon in the soil goes beyond that of a key indicator for determining soil quality, as, if released, it will contribute to an increase in the greenhouse effect. 

Changes in land use are among the main sources of anthropogenic carbon emissions into the atmosphere. When the soil is cultivated and managed, changes occur in the efflux and influx of CO2 at the soil-atmosphere interface, especially through plowing and harrowing operations, as these lead to greater oxidation of organic matter when in contact with the air. These carbon emissions also occur through altered water regimes, erosion and fires.

Climate change mitigation

Among the various solutions to mitigate climate change, an important option is carbon sequestration in agroecosystems, especially in agricultural soils. Furthermore, the carbon stock in the soil could compensate for anthropogenic emissions, benefiting agricultural productivity and mitigating the increase in temperature. For carbon sequestration to occur in the soil, management systems must seek to maintain high amounts of biomass, cause minimal disturbance to the structure, in addition to promoting soil and water conservation. These practices also increase the activity and diversity of soil fauna – a significant number of organisms that inhabit the soil –, strengthening the mechanisms of element cycling. 

The maintenance of organic matter in the soil influences flocculation, that is, it reduces the removal of clay from the soil, either by forming bridges between particles, or by favoring their union and increasing their structural stability in soils, especially electropositive soils.

Furthermore, after the death and decomposition of the root system, canaliculi or biopores remain, which, associated with the holes constructed by the movement of meso and microorganisms in the soil, enlarge the drainage and lead to increased aeration and water infiltration into the soil. Cultivation systems have a great influence on the physical quality of soils, especially on the size of the pores and, consequently, on their structure.

What is the Direct Planting System?

It is considered the most effective and conservationist tool in modern agriculture for the sustainable exploitation of agricultural production systems. It is based on the diversification of species, via crop rotation and intercropping, with no or minimal soil disturbance and soil cover with straw. It is essential to maintain the physical, chemical and biological characteristics, ensuring the sustainability of the soil.

Unlike other management systems, the SPD recommends the use of integrated agronomic practices that make it technically and economically viable to continuously sow or plant without prior soil preparation, crop after crop, for an indefinite period of time.

Production systems conducted using direct planting require less infrastructure and human labor, consume less fossil energy, reduce erosion, require lower doses of correctives and fertilizers and favor the integrated management of pests, diseases and weeds. Therefore, at the same time as they improve the quality of soil, water and air, they increase the income generated by agriculture.