Soil survey of the east coast and the central highlands indicates need to update Madagascar soil map

Abstract

ABSTRACT The soil map of Madagascar has not been substantially updated since the 1960s. The number of reported soil profiles that meet the criteria of the Reference Pedon Description – the highest level of data reliability used to ascertain FAO soil unit classification – is also limited for a country-scale soil map. Therefore, we conducted a soil survey in the east coast and the central highlands, the most populated and major food-producing areas in Madagascar, to assess need for reconsideration of the current soil map. As compared to the latest soil map, our results indicate that Ferralsols cover less area on the flat terrains from the east coast to the central highlands and that Geric Ferralsol is more frequently observed soil type rather than Haplic Ferralsol on acidic rocks. The soil type of paddy fields in the southwestern plain of Lake Alaotra – the country’s largest rice-producing region – was Vertisol with a hydragric horizon rather than Histosol. This is attributed to long-term paddy cultivation in the region or the difference of the definition of peat soils between the current and old soil classification systems. The volcanic-origin soils that sporadically exist in the central highlands can be classified as Eutric Andosol rather than Eutric Cambisol. These results show the need for updating the current soil map based on the quantitative data and also have important implications regarding the land history and for appropriate land management in agriculturally intensive areas in the east coast and central highlands of Madagascar.