FAO publishes first global assessment of soil organic carbon in grasslands

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Improving management practices in grasslands—large areas covered with grass, especially used for animal grazing—can boost the capacity of soils as carbon sinks, and help countries reach their climate goals, according to a new report by the Food and Agriculture Organization of the United Nations (FAO).

After oceans, soils are the second largest carbon pool on earth and they play an important role in global climate change due to the large amount of carbon currently stored in soil organic matter.

The first FAO Global assessment of Soil Carbon in Grasslands measured the baseline of stocks of Soil Organic Carbon (SOC)—the carbon held within the soil that is measurable, expressed as a percentage by weight (gC/Kg soil)—in both semi-natural and managed grasslands and estimated their potential of SOC sequestration.

The study found that if the SOC content in the 0-30 centimer depth layer of available grasslands increased by 0.3 per cent after 20 years of the application of management practices that enhance soil organic carbon sequestration, 0.3 tons C/ha per year could be sequestered.

“Assessing the current state of grassland systems and their potential to sequester carbon in the soil is key to better understand the benefits of grassland services for food security, biodiversity conservation and climate change mitigation.”

Thanawat Tiensin, Director of FAO’s Animal Production and Health Division

“This report provides a comprehensive analysis of the state of carbon stocks and potential offsets in grassland soils in the world. It can be also used as a baseline for future works to enhance soil carbon sequestration through sustainable grazing management,” he added.

Importance of grasslands

Soils can act as both sources and sinks of carbon, and many grasslands, which contain approximately 20 per cent of the world’s SOC, have suffered losses because of human activities such as intensive livestock grazing, agricultural activities and other land-use activities.

According to the report, most of the world’s grasslands have a positive carbon balance, meaning the land is stable or well-maintained. However, negative carbon balance was found in East Asia, Central and South America, and Africa south of the Equator, meaning these stocks are likely to be decreasing due to anthropogenic stresses combined with climatic conditions.

This trend, however, could be reversed by stimulating plant growth, capturing carbon in the soil, and protecting carbon in highly organic soils, such as semi-natural (non-human managed) grasslands.

In livestock management, this could also mean implementing rotational, planned or adaptative grazing measures for animals.

Case studies

The report also explores other possible measures to improve SOC stocks through case studies, such as the establishment of fodder gardens in eastern African countries.

More than 40,000 small farmers in Kenya and Uganda have established gardens with calliandra trees as a practice to raise milk production and improve cow health.

The trees have had remarkable success in conserving soil, nutrient cycling and nutrient retention, but little is known regarding their potential of sequestering carbon in the soil.

According to the study, the establishment of these gardens has a potential increase in soil carbon of 0.03 tons C/ha per year.

The report also explores options considering grazing systems intensification in response to increasing demand for livestock products and land competition.

These include enhancing carbon inputs from plant roots and residues by managing plant biomass removal from grazing or increasing forage production through improved species, irrigation and fertilization.

Limitations

The study pointed out that the lack of incentives for farmers to improve management practices, and the current difficulty in accurately monitoring SOC stocks and changes are the main reasons that SOCs are not being included in the national climate plans known as National Determined Contributions (NDCs), which are at the heart of the Paris Agreement.

The results of the report could support the inclusion of SOC targets in NDCs, improving their transparency for tracking and comparing policy progress related to soils.

The authors also underscored that the estimation of the global soil carbon stock is still quite uncertain and improved geostatistical methods and data accuracy related to soil, animal and vegetation properties and their carbon exchange are urgently needed.

“It is crucial to generate local datasets, especially from underrepresented regions [e.g., Africa], and explore differences among existing datasets,” they said.

The SOC stocks presented in the report can be used as a baseline for future work to explore the impacts of livestock management on soil carbon at country and farm levels. However, there is still a strong necessity for additional data on current soil conditions, especially from underrepresented regions.