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.

In Madagascar Highlands, population pressure and intensive rice cultivation in the lowlands has led to cultivation on the fragile, low fertility soils of the hillsides. Fertilisation being limited, yields remain low while erosion leads to paddy field silting-up and destruction of downstream infrastructures. To overcome these problems, experiments on direct planting on permanent soil cover (DPPSC) have been conducted since 1991 in the Andranomanelatra farm and since 1994 in farmers' fields, covering a wide range of biophysical and socio-economic situations

Influence de la fréquence et de l'intensité de la combustion selon le type de sols de tanety

En Afrique, le prix élevé des engrais, ou leur indisponibilité, empêche les agriculteurs aux faibles ressources d'intensifier les cultures sur les sols dégradés, peu fertiles. Sur les Hautes-Terres malgaches, la saturation des bas fonds rizicoles et la forte pression démographique accélèrent la mise en culture des collines aux sols essentiellement ferrallitiques, pauvres et fragiles. De plus, sous l'effet des basses températures, la matière organique évolue lentement et piège des éléments utiles pour les plantes (Chabanne et al., 1996). Le sol soumis aux feux de brousse et aux labours successifs, subit une érosion qui ensable les rizières et détruit les aménagements. Face à ces contraintes, l'écobuage associé au Semis Direct sur Couverture Végétale Permanente (S.C.V.) a été expérimenté afin d'améliorer durablement la productivité avec un minimum d'intrants.