Joseph Randriarimalala and Bodonirina Rasoloarisoa, a farming couple in central-eastern Madagascar, noticed that their half-hectare land was becoming less and less fertile and producing lower yields, but they did not know why and what to do. Now they do – degradation of their land is the result of increased soil erosion due to the farming approach they used to employ on their hilly terrain.
“We used to plant seeds right on the slopes, using machinery to turn the soil around. It turns out that this can lead to a loss of the topsoil layer, the most fertile part of the soil,” said Randriarimalala. Scientists from the country’s National Institute of Nuclear Science and Technology (INSTN Madagascar) used an isotopic technique to evaluate the level of soil erosion on the couple’s plot (see Fallout radionuclides help to assess soil erosion) – and then used the results to advise farmers in similar situations across the country.
According to the Food and Agriculture Organisation of the United Nations (FAO), around one-third of the island’s land resources is degraded – mostly due to erosion. Erosion does not only deplete the soil, but at the same time impacts terrestrial ecosystems and their biodiversity, and when the eroded soil ends up in rivers and lakes, it affects the viability of aquatic ecosystems as well.
It is therefore important to establish effective conservation strategies, said Emil Fulajtar, a soil scientist at the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, who advised ISTN scientist on the matter. Erosion hotspots and the effect of the conservation strategies were determined using isotopes.
The studies have revealed that on cultivated land in the country’s Central Highlands over 10 tons/hectare of soil are lost on unprotected slopes every year as a result of a combination of farming practices, the lack of land cover and natural causes such as wind and heavy rain. The solution the INSTN researchers recommended to farmers was to switch to terrace farming, in which measurements revealed the loss of fertile soil was only 5 tons per hectare per year, said Naivo Rabesiranana, who headed the research at INSTN. “This is still a lot as compared to forested areas, but it is much less than before,” he said.
A nuclear technique demonstrated that turning tilled slopes into terraces on central Madagascar’s hilly terrain saves much of the soil that would be lost to erosion. (Photo: M. Gaspar/IAEA)
They chose the family plot of Randriarimalala and Rasoloarisoa for the experiments because its location and climate is representative of much of the agricultural land in the country’s highlands, the central and most populous area of Madagascar around the capital Antananarivo. Officers from the Ministry of Agriculture are now working directly with highland farmers on implementing conservation strategies based on these findings.
The land in Madagascar is extremely fertile and the climate is so favourable to agriculture that farmers here can afford four harvests per year – in other words, this family’s half-hectare land is equivalent to a two-hectare plot in a more temperate climate. Farmers in Madagascar’s highlands have always been rotating their crops to maintain the nutrient level of their plots, but now they know that at least once a year they need to grow sweet potatoes or beans, plants with extensive roots that not only keep much of the soil in place but after they have decayed enrich the soil with carbon and provide a more dense structure to the soil, slowing down erosion.
“There are many ways in which the IAEA, through its technical cooperation programme, is assisting Madagascar in the use of nuclear techniques for development, in support of the government’s priorities,” said Abdou Ndiath, the IAEA Programme Management Officer works with the country’s government. “Addressing land degradation challenges brought about by soil erosion is among the most important fields of cooperation.”
How Fallout radionuclides help to assess soil erosion
Fallout radionuclides (FRNs) are present in the atmosphere and are deposited on the earth’s surface through rain. Therefore, on land, they occur only in the topsoil layer and when this layer is removed by erosion, their concentration is reduced. This reduction indicates how much soil has been removed from a particular location.
When the FRN method is used on a site where soil conservation measures have already been applied, the results are compared to those on a site with conventional land management, the efficiency of soil conservation measures in controlling soil erosion can be evaluated.
Source: https://www.iaea.org
