Impact of a DMC rainfed rice-based system on soil pest and Striga infestation and damage in Madagascar

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Direct seeding, Mulch-based, Conservation agriculture (DMC) systems are being extended in Madagascar in view of reducing erosion and loss of fertility of hill slope soils observed in conventional rainfed systems. However, little is known on their effects on infestation and damage to crops (particularly rice) by soil insect pests and Striga. While in the regions around Lake Alaotra and Manakara, dramatic damage by black beetles (Heteronychus spp.: Coleoptera, Scarabaeidae) was observed on rice cropped on mulch , attacks by these pests were reduced after a few years of DMC management in the Highlands of the Vakinankaratra region . On the other hand, in the Middle-West of Vakinankaratra, where Striga asiatica (Scrophulariaceae)has become a major constraint to staple cereal crop cultivation in rainfed systems, infestation of rice and maize by this parasite was drastically reduced after just one year of DMC management based on dead or live mulches, compared to the traditional plough-based system . The objective of the studies presented was to elucidate the factors accountable for reduction in infestation and damage by soil insect pests and Striga in DMC rainfed rice/soybean-based systems, with particular emphasis on its effect on natural enemies of pests.

Mots-clés : Riz, Arachis pintoï, Les Hautes Terres , Adventices, petite agriculture familiale, scv

Direct seeding on plant cover with soil smouldering techniques

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The soils in hilly and densely populated areas in the “Hautes-Terres” region of Madagascar are mainly ferrallitic and thus fragile, relatively infertile and prone to erosion. In addition, under low temperature conditions, organic matter breaks down very slowly and traps nutrients that are essential for crops. Direct seeding systems on plant cover offer a broad range of benefits, including erosion control and soil fertility enhancement. However, yield mprovements are low because farmers —focusing chiefly on their immediate survival— apply very little fertilizer. Facing these constraints, soil smouldering, associated with direct seeding on vegetal cover, should allow a sustainable improvement of the production, with minimum inputs.

Mots-clés : écobuage, fertilité, scv, biomasse

Developing sustainable cropping systems with minimal inputs in Madagascar: direct seeding on plant cover with soil smouldering (écobuage) techniques

 acte de colloque | |     

In the Hautes-Terres region of Madagascar, population pressure is accelerating the conversion of hilly areas with fragile and relatively infertile soils into cropland. As fertilizers are limited, crop yields remain low and erosion is destroying rice fields. Instead of clearing areas fallowed with Aristida sp. by burning, ibis biomass can be kept for use as mulch and for ",soil smouldering", (écobuage). The effects of this strategy were found to be spectacular, i.e. boosting rainfed rice yields to levels that could bc achieved with high chemical fertilizer inputs-to which farmers have no access for financial reasons. All fuels used (Aristida sp. or barley straw, rice husks, and Acacia mearnsii branches) significantly inereased crop yields relative to the control (without soil smouldering). A residual effect was noted in the second year, especially on volcanic soils with high organic matter levels. Hence, sustainable cropping systems that fulfil farmers' needs while protecting their rice fields can be developed through the use of soil smouldering-performed just once to boost soil fertility-associated with direct seeding techniques.

Mots-clés : écobuage, Riz, Les Hautes Terres , mulch, soja, fertilité, scv