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.

Pour les rizières avec un mauvais contrôle de l’eau (terrasses sans accès à l’eau par exemple), le semis direct de variétés de riz pluvial ou mixtes (irrigué x pluvial) sur une couverture végétale d’avoine peut être proposé. L’avoine peut aussi être utilisée comme fourrage pendant l’hiver (quand la disponibilité en fourrages est faible)

Dans les systèmes de culture traditionnels en zone de montagnes au nord du Vietnam, le riz pluvial est cultivé 2 à 5 ans après abattis et brûlis de la forêt, et est suivi par un ou deux ans de culture de manioc. La terre est alors abandonnée pour 10 ou 20 ans, jusqu’à ce que la culture soit de nouveau possible. L’installation d’un couvert de Stylosanthes guyanensis sous le manioc améliore le sol et permet une remise en culture immédiatement après la culture de manioc.

La diversité des systèmes de culture avec couverture végétale mis au point permet de proposer une large gamme reposant sur différents niveaux de technicité requise (du plus simple au plus exigeant) et différents degrés d’efficacité des fonctions de régulation du fonctionnement Sol - Plante. Cette diversité peut être schématisée en quatre grands types de systèmes.

Brachiaria ruziziensis est une graminée très feuillue, stolonifère et pérenne (> 3 ans). Elle produit rapidement une forte biomasse (jusqu’à 15 t/ha en 3 mois). Son puissant système racinaire capable de mobiliser des éléments minéraux dans des sols difficiles (compactés, acides et à toxicité aluminique) lui confère une large adaptabilité dans le cadre des systèmes de culture en semis direct. Notamment, ses capacités de décompaction le placent comme un précédent idéal pour le riz pluvial.

Developing and maintaining water control in paddy fields is difficult, costly and requires sufficient water reserves. Thus, even in the main rice growing area of Madagascar, the Alaotra lake region (800 metres above sea level), only 30 000 ha of paddy fields can be properly irrigated when over 70 000 ha will remain under poor water control. In these fields, traditional techniques based on irrigated cropping practices are very unreliable: late transplanting (which can be done only when sufficient water is available) and occurence of dry conditions at the end of the plant cycle lead to usually low yields (0.8 to 1 t/ha on average) and production is very unreliable (from nil, during the dry years to 3t/ha when rains are favourable), which makes crop intensification very hazardous. For such situations, a change in paradigm is proposed: abandoning irrigated practice and making the choice of growing upland or ",poly-aptitude", rice varieties (SEBOTA) with agro-ecological practices adapted to the specific field water regime.

Avec ces techniques de semis direct sur couverture végétale, le sol est protégé en permanence et les adventices contrôlées par le paillage. L’enracinement profond,la structure du sol améliorée et l’activité biologique intense conduisent à augmenter l’efficacité de l’utilisation de l’eau et des éléments nutritifs, pour une agriculture rentable mais durable et préservant les ressources naturelles.

In the "Cerrados" of Central Brazil, direct seeding mulch based cropping systems (DMC) applied by farmers have been adapted to tropical conditions (high temperature,high rainfall and resulting high rates of organic matter mineralization). Generally, time saved with no-tillage allowed farmers to plant another crop in the same year, producing additional biomass, increasing thereby organic matter entries into the soil,and maintaining the soil surface always covered and protected from soil erosion (pictures). However, the level of biomass restitution, and the long term impact on C sequestration in DMC systems will differ in function of the type of commercial crop rotation, the species used as cover-crops, the level of productivity and the farmer's management (Séguy et al., 2003.

The soil organic carbon (SOC) content depends strongly on soil management and especially the level and quality of organic restitution to the soil. The SOC pool is the net result of carbon (C) input in the form of crop residue and biomass, and output including CO2 flux and other losses (Duiker, 2000). Changes in soil management can alter SOC content. A substantial increase in the SOC content in the 10 cm topsoil layer in no-tillagesoils compared with soils under natural vegetation and long-term conventional tillage (CT) (Séguy et al. 2003 ) can occur due to high crop-residue input and lack of soil disturbance.

Agriculture in Madagascar has to face tremendous constraints: very low investment capacity, poor infrastructure network, low availability and high prices of inputs, uncontrolled bush fires and deforestation leading to severe erosion, loss of arable land and destruction of downstream infrastructures. As a consequence, yields are low and farmers' condition very precarious. Techniques of direct planting on permanent soil cover (DPPSC) can lead to solutions for sustainable and profitable agriculture.