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Return to Traditional Terracing Improves Farm Production in Madagascar

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In Madagascar, where farming has moved toward modern intensive agricultural practices in recent decades, a study has demonstrated that the country’s farmers would be much better off if they returned to the traditional terrace farming of their ancestors. Using isotopic techniques to study erosion patterns of the island country’s mountainous regions, where more than 30 percent of the agricultural area is already degraded, the Joint FAO/IAEA Division found that terracing systems could reduce soil erosion by 40 percent.

Astronauts once reported that Madagascar looked as if it were bleeding to death. Today, looking at a satellite view of the country makes it easy to see what they meant. The image shows reddish rivers and reservoirs – not filled with blood but with the country’s red ferralitic soil that is eroding down the island’s steep slopes, leaving agricultural land barren and adding sediment and its polluting nutrients of nitrogen, phosphorus and potassium to water systems.

Due to deforestation and improper farming practices, Madagascar, one of the world’s poorest countries, loses more topsoil per hectare each year than just about any other country in the world. The soil itself is not particularly fertile and now it has to deal also with the impacts of climate change, such as drought, floods and unpredictable rainfall that further break down the soil structure and makes it more likely to erode.

In order to help Madagascar’s farmers with conservation practices, scientists at the Institut National des Sciences et Techniques Nucléaires (INSTN-Madagascar) in the capital, Antananarivo, worked with Joint FAO/IAEA Division experts to address the problem and identify the country’s most erosion-prone areas. The Joint FAO/ IAEA Division assists countries in quantifying soil erosion rates and assessing the effectiveness of their soil conservation practices. In the case of Madagascar, this called for using isotopic techniques to investigate and compare soil erosion rates in terraced and non-terraced agricultural fields.

Fallout from past nuclear testing allows scientists to quantify and map erosion

Highly-sensitive nuclear techniques allow scientists to track certain atoms, such as caesium-137 and lead-210, in soil to determine the soil’s movement and its conditions. Caesium-137 first came to earth as radionuclide fallout following atmospheric nuclear testing in the 1950s and 1960s. As it was not there before, and because it binds strongly to soil particles, it now can be used as a soil marker to ascertain and compare soil movements in the landscape. Lead-210 on the other hand is a naturally occurring fallout radioisotope that can also be used as a soil tracer.

In cooperation with the Joint Division and through the IAEA’s technical cooperation programme, INSTN received the necessary equipment and its staff was trained in how to collect soil samples and measure their radionuclides content and analyse the data. With that analysis, they concluded that if farmers would apply the same agricultural practices as their ancestors – and create terraces – they could reduce run-off and, in turn, soil erosion in the country by up to 40 percent, when compared to non-terraced agricultural fields, and thereby retain at least 3 tonnes of soil per hectare every year.

In addition to identifying key areas with high erosion and sediment transfer, fallout radionuclide methods also enable better targeting of soil conservation measures. This increases farmers’ ability to control and mitigate soil losses caused by erosion and to mitigate its environmental impact.

While the story of Madagascar is dramatic, it is just a part of a global situation that each year sees as much as 36 billion tonnes of fertile soil being lost from world agricultural systems through soil erosion. In economic terms, the onand off-farm soil erosion costs for farmers and the world’s land systems are estimated at USD 400 billion per year. Hardly surprising that the Joint Division receives requests for technical support from numerous countries around the world.

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