Farmers Dynamics For Building Soil Fertility In Peri-Urban Market-Gardening Farming Systems In The Antananarivo District (Madagascar)

The supply of fresh vegetables to growing cities is a major challenge in developing countries : agriculture near the cities plays an important role. The territorial dynamics of suburban market-gardening has been analysed in the case of the district of Antananarivo (Madagascar). On-farm surveys show the saturation of the alluvial ridges along lowland rice fields called baibobo and traditionally devoted to market-gardening. Over the past decade, market-gardening areas have increased through colonization of the poorly fertile hills (lonely) formerly devoted to cattle pasture and secondarily to some food crops (cassava). The conquest of lonely for vegetable crops is correlative to the introduction in the farming system of a small herd of cows with dual purpose : milk production (sold in the town) and production of manure for market-gardening. The construction of lonely fertility over time by farmers shows common phenomena: a mix of crops with different cultural cycle lengths and of various fertilizers applied on them, always including manure. To account for the evolution of this fertility, an indicator of chemical fertility was built on a set of plots of different ages of cultivation and strongly linked to the performance of the leading local crop, tomatoes. The chemical fertility of lonely at the end of the fertility construction process is found to be similar to that of baibobo. However, this dynamics is now hampered by the constraints on increasing the number of cattle: competition for land use between cattle feeding and vegetable crops on lanety is limiting the quantity of manure because its management is very time consuming. Therefore, the use as fertilizer of an urban compost made by riddling urban wastes in the Antananarivo clump has been successfully tested as an alternative and could be a future fertilizer source at least partially replacing cattle manure.