Integrated crop-livestock system shows soil carbon accumulation rate three times higher than in grain crop succession

• Arrangements with integrated crop livestock system showed carbon accumulation rates of 0.6 t and 0.9 t per hectare.

• Result represents threefold increase in soil carbon stocks in comparison with high-performing soybean-corn succession systems.

• Recorded rates are above the recommended by the International ″4 per 1000″ Initiative, an organization that joins research and education institutions’ efforts on soils for food security and climate around the world.

• Findings can be partially explained by the presence of Brachiaria grass, a forage plant that grows roots deep into the soil.

A study by Embrapa Rice and Beans estimated the soil organic carbon (SOC) accumulation rate in a Cerrado soil in Goiás state, Brazil, by comparing integrated crop-livestock system (ICLS) with a grain crop succession (soybean-corn) system in both no-till and conventional farming. The findings show an increase in soil organic carbon stocks in ICLS in the course of 20 years, projected for the period from 2019 to 2039.

The projection of the carbon accumulation was stipulated for the soil profile depth of 30 cm. The result was that the highest carbon accumulation figures were found in ICL systems under no-till farming conditions; two of which (ICLS1 and ICLS2, as shown below) presented SOC increase at rates between 0.6 and 0.9 metric tons per hectare per year, respectively. It represents a threefold increase in soil carbon stocks in comparison with the highest performances of soybean-corn crop succession systems, which reached carbon accumulation rates of 0.11 and 0.21 tons per hectare per year in no-till farming.

The simulation

The study was based on the historical data series of sowing and management in an ICLS area at Fazenda Capivara, a farm that belongs to Embrapa, located in Santo Antônio de Goiás, Goiás, Brazil. The information recorded in the management database since 1990 has supplied a model known as CQESTR, which simulates carbon behavior in crop soils and is used to predict how different management practices affect carbon dynamics.

Photograph: Maria Eugênia

During the study, two ICLS were simulated within CQESTR and replicated along the assessment period. The first one (ICLS1) included corn cropping in the summer harvest followed by 4.5 years of Brachiaria pasture. The second (ICLS2) had soybean as its summer harvest, followed by fallow in its first year, then upland rice, new fallow for the second year, a corn crop, and, eventually, 3.5 years of Brachiaria pasture. Regarding the (soybean-corn) crop succession system, it comprised either alternating annual summer crops, as well as periods of fallow, or succession between both crops (harvest and off-season harvest).

Beata Madari is one of the Embrapa researchers responsible for the study. She said this result is in line with previous ones in the field and can be explained by the presence of Brachiaria forage, which presents deep roots in the soil and thus not only recycles nutrients but also helps to increase carbon stock in the system due to the contribution of the aerial and root biomass in ICLS. According to Madari, a carbon accumulation rate of 0.9 tons per hectare per year surprised the researchers, because it is a high value taking into consideration the initial diagnosis of the Embrapa farm: a clay soil (over 50% of clay) and a low to medium carbon content (approximately 2%).

International network

The result achieved by the scientific study can be compared to other studies on soil carbon stocks. One of the main organizations in the world related to the topic is the International ″4 per 1000: Soils for Food Security and Climate″ Initiative. The initiative comprises an international network of collaborators, which includes research and education institutions, farmer associations, governments, international organizations, as well as agroindustry and business sectors. It advocates sustainable soil management practices to reach an annual growth rate of 0.4% (4% or 4 per 1,000) in world soil carbon stocks. For the conditions in the experimental area in the Brazilian Cerrado biome, that means 0.26 tons per hectare per year. However, this rate may vary, depending on local climate and soil conditions.

For the researcher Beata Madari the research results were superior, which shows that the sustainable management of the soil and crops in the Cerrado biome may play an important role to mitigate greenhouse gases like carbon dioxide (CO2).

The International ″4 per 1000″ Initiative was launched during the 2015 United Nations Climate Change Conference (COP21) in Paris, France. Embrapa is one of the members of this initiative, and the researcher Beata Madari is part of the technical-scientific committee.

Carbon market

The annual carbon accumulation rate found in this study for the ICLS under no-tillage conditions raises new elements for scientific debate. According to the Embrapa researcher Pedro Machado, there are other studies that found higher amounts of carbon capture in ICLS: annual rates of up to 1 ton per hectare per year. However, Machado says these have usually been small-scale studies, in parcels, lasting few years or harvests. In this sense, he considers the use of the CQESTR model a differential. ″The simulation tool was essential because it allowed us to effectively use the nearly 30 year-old database of crops at Embrapa’s farm and predict, for a period, the carbon accumulation dynamic according to soil preparation and agricultural management. Thus, we could extend the time for analyzes of the effect of ICLS on carbon sequestration and reach a result we believe best predicts the behavior of the production system″, the researcher comments.

Machado adds that CQESTR is a program used for scientific investigations both in Brazil and in other countries, but, for Brazilian situations, it had only been used in some tropical regions of the Northeast and Southeast, and now it was tested and approved for Cerrado conditions.

The researcher also mentioned the study not only opens doors to accurately quantify the carbon stored in the soil in a specific agricultural system, but also allows the future projection of how much carbon will be stored in the soil. This study, for instance, stipulated the projection for the period from 2019 to 2039. This prospect, according to Machado, has the research become a support and qualification point for the ongoing debate in Brazil about the regulation of a carbon market, and establishes essential strategies for agricultural sustainability and for the development of national public policies.

The study is part of Janaína de Moura Oliveira’s doctoral thesis. It was carried out at the Federal University of Goiás (UFG) and is entitled: Carbono no solo em sistemas integrados de produção agropecuária no Cerrado e na transição Cerrado-Amazônia [Carbon in soil of integrated agricultural production systems in Cerrado and Cerrado-Amazon transition]. The study counted on the collaborations from Embrapa Labex USA and University of Arkansas (UARK). The thesis can be downloaded here.

Better soil health

The study showed that in both ICL and crop succession systems soil carbon stock was higher in no-tillage production than in conventional tillage systems (plowing and harrowing). The Embrapa researcher Márcia de Melo Carvalho, who participated in the study, observed that conservation practices, such as no-tillage, contribute to carbon accumulation in comparison with conventional systems, since not tilling the soil favors greater structuring, with the formation of aggregates (small clumps of soil) that ″pack″ organic matter (check specific study here), protecting it from rapid decomposition. The more organic matter, the more saturated with carbon the soil is.

Photograph: Sebastião Araújo

However, something as important as soil carbon saturation is the protection afforded by no-tillage. No-till farming systems allow the formation of a layer that protects the soil (mulch) from the impact of rain drops, providing for water infiltration and the regulation of soil temperatures. Additionally, the scientist says management practices that result in soil carbon accumulation also improve quality and yield in production systems by adapting to environmental changes, which are a reality the Cerrado in Goiás state.