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Carbon storage: contribution is the more important

© IRD/Eric Blanchart Direct seeding under plant cover - here bean cultivation on rice residues -, two of the pillars of conservation agriculture

After 15 years of cutivation in line with climate-smart agriculture in Madagascar, researchers are definitive: soil carbon storage increases thanks to these methods, but with a great variability. It is therefore necessary to think on a territorial scale.

Ensuring food security; adapting methods to climate change; and mitigating the greenhouse effect: these are the three objectives of Climate Smart Agriculture (CSA).

To achieve this, different agricultural practices coexist, that do not all produce the same results. This is the conclusion of the synthesis work carried out by Tantely Razafimbelo, at the Radio Isotopes Laboratory in Antananarivo, and Alain Albrecht, of the Eco&Sols unit of the IRD, on various experiments carried out in Madagascar.

An innovative agriculture

"At the beginning, the spirit of Smart Agriculture - the initial concept - was quite simple: it was inspired by the notion of smartphone, smartcar and wanted to be a connected, innovative agriculture to help farmers, recalls Alain Albrecht. Rapidly, it has integrated the reality of climate change and its necessary adaptation, to become Climate Smart Agriculture." Practising a more productive agriculture that adapts to climate change while providing carbon sinks in the landscape are therefore the two sides of the CSA.

Carbon sinks? Areas that store carbon in the soil. This sequestration of atmospheric carbon, through photosynthesis and subsequent decomposition of plants, is one way to help reduce the greenhouse effect.

Different agricultural practices

For the past 15 years, in collaboration with NGOs and research institutes, including IRD, Malagasy farmers have been testing different practices: conservation agriculture, which is based on reducing tillage, permanent cover to reduce erosion and diversified rotations; agroforestry, which consists of associating trees with crops and the use of organic amendments, whether it is manure or compost.

To determine which is the most effective in improving carbon sequestration, the scientists used two approaches: comparison of the carbon stock with that of a conventionally managed plot; and comparison between the stock at the time of implementation and after x years.

Reasoning at the landscape level

The results indicate a high variability: the stock difference for conservation agriculture ranges from 0 to 1.82 Mg C/ha/year (megagram (tonne) of carbon per hectare per year), while in agroforestry, the difference with slash-and-burn farming is 0.68 Mg C/ha/year and the use of organic inputs leads to increases of 0.16, 0.81 and 0.42 Mg C/ha/year.

"Finally, what matters is the supply of organic matter: the more organic matter there is, the more carbon can be stored in the soil," explains Alain Albrecht. There is then the question of the availability of resources. If you want to increase manure intake, for example, you need to increase production and therefore livestock production. This requires strengthening the cultivation of fodder... It is then necessary to reason at a landscape, or territorial, scale because a single farm does not necessarily contain all the resources!"

For Alain Albrecht, this spatial dimension also offers the interest of working with new partners: producer associations, regional structures... and reconnects with the co-constructive and participatory aspect of climato-intelligent agricultural research.

This text is a press release of IRD translated in English by Afriscitech

Reference: T. M. Razafimbelo et al., Cahiers Agricultures , 27, doi : 10.1051/cagri/2018017, 2018

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