Tunisian climate is mediterranean, characterized by irregular, sudden, intense and relatively low rain-fall. Land degradation is continuing, water resources are becoming scare, and energy cost of farm products is continuously getting high. Consequently, cereal producers can hardly make an economic return, while practicing conventional agriculture based on conventional drilling (CD). Conservation agriculture based on direct drilling (CA/DD) gives farmers a chance to protect soils and rebuilt their fertility for an efficient use of any available form of water (rain-fall, irrigation). Such desirable efficiency does not come only by the use of the appropriate crop species, but necessarily by reducing water evaporation. To do so, a permanent mulching on the soil surface is the pivot of CA/DD. Since rain-fall fluctuates from one year to another, crop sequences should parallel with such conditions. Some couloirs have early rains (September-October) and late rains (May-June) too. In Bou-Salem (Governorate of Gendouba), early and late rains accounted for 26.2 % and 19.9 % of the 07/08 total rain for cereal growing season (September/07-June/08), respectively. These rains are not well capitalized in cereal production, when applying conventional agriculture. So, coupling the site specific approach and agronomy of opportunity is imperative to lift up farm productivity. The climate (rain, heat) of production sites should be characterized to better define growing seasons and make the appropriate agronomic sequence. Then, the agronomy of opportunity (producing the maximum of biomass whenever the climate and the biology of the desired crop are favorable) could be applied in different scenarios, under rain-fed and/or irrigation conditions. There is no static scheme to crop the land, and it is rather a dynamic management of soil, crops, and water. A particular emphasis should be put on use of strictly seasonal (fall, winter, spring, summer) cereals and legumes in order to make a continuing cropping with two-three crops a year. A potential scenario could be a fall-barley/springpeas/ summer short season-sorghum hybrid.

Diaporama présentant les problèmes malgaches: érosion et feu de brousse entraînant perte de fertilité , climats et géographie; GSDM et SCV avec historique et résultats jusqu'à diffusion

The comparative advantages of DMC rainfed cropping systems

Diaporama sur Jachères cultivées de Légumineuses type Téphrosia sp., Sesbania sp., Crotalaria sp., et essais pour déterminer l'érosion par simulation des pluies

Diaporama sur nouveaux systèmes Sorgho + Mucuna au Sahel, érosion et ruissellement, Rétention par Zaï, fumure minérale ou organique

The present study was carried out in the cotton belt in the Far-North Province of Cameroon. It has been focused on the physical properties of soils under mulch-based cropping systems. The experimental design was drawn from one on Direct seeding Mulch-based Cropping system (DMC) trial location under a controlled conditions in the region of Kaéle (700-800 mm mean annual rainfall), and where a network of 20 farmers is carrying out on-farm trials in the region of Maroua (800 mm mean annual rainfall),. Plots under mulch-based cropping systems established 2, 3 or 4 years ago were compared against farmers' traditional plots under direct seeding without mulch or with tillage practice. These plots were cropped with sorghum or cotton. Using the gravimetric method it has been shown that the apparent density of soils on the upper horizons under DMC was lower compared to soils from the farmers' traditional cropping systems. Bulk density values lie between 1.2 g/cm3 to 1.5 g/cm3 against 1.6 g/cm3 to 1.7 g/cm3 for farmers' traditional control plots. These results are due to an increase in soil porosity induced probably by a higher soil biological activity. A better water infiltration was also obtained'under DMC against the farmers' traditional systems. These mean infiltration values were obtained using the double ring and «Beer can» methods, and lie between 0.9 to 5 mm min-1 for the mulch-based system against 0.6 to 1 mm min-1 for the farmers' traditional systems. This study shows that after a period of less than 3 years under DMC an improvement of the physical properties of the soil was clearly obtained, notably soil porosity and consequently soil water dynamics. This improvement affects the soil water availability and therefore water supply to the crops.

Le rythme d'adoption des SCV en petite agriculture, en tant que nouveau paradigme, serarelativement lent et se fera à l'échelle de une ou deux générations. Les effets néfastes duchangement climatique apparaîtront avec un rythme comparable. Raison majeure pouraccélérer la diffusion là où les SCV ont déjà été implantés et pour commencer le plus tôtpossible ailleurs.

Une gestion au plus près du biologique des cultures en rotation, avec substitution progressive des molécules chimiques par des molécules organiques (qualité biologique des sols, des produits et des eaux) ; Une priorité à la diffusion-adaptation des SCV qui intègrent l’élevage et contribuent au regain de biodiversité dans les agricultures familiales défavorisées au sud avec l’objectif de s’engager durablement dans la lutte contre la pauvreté.

Le présent mémoire a pour objectif de caractériser les systèmes de culture sans labour avec couverture végétale et leurs conditions d'intégration au sein des exploitations agricoles.La méthodologie de recherche a consisté en une revue bibliographique sur le SCV, des rencontres avec des personnes ressources et une enquête auprès d'agriculteurs.Depuis 2000, la totalité de l'exploitation du paysan enquêté est en SCV avec couverture morte. Selon lui il s'agit de protéger et dynamiser les activités biologiques sur la structure et la matière organique de ses terres. L'adoption de la technique lui a imposé des adaptations de systèmes de culture à différentes échelles, de la parcelle à l'exploitation. Selon l'agriculteur, les quantités d'herbicides ont diminué et le glyphosate avec les rotations est maintenant l'élément essentiel du contrôle des mauvaises herbes. La technique du SCV a un intérêt particulier dans cette exploitation car elle permet l'accès aux parcelles mouillantes (situées dans la vallée du Cher) pendant de très longues périodes, ce qui permet de semer et apporter les engrais aux dates optimales.

Artigo originalmente publicado sob o título Impacts des systèmes de culture en semis direct avec couverture végétale (SCV) sur la dynamique de l'eau, de l'azote minéral et du carbone du sol dans les cerrados brésiliens, no periódico Cahiers d'études et de recherches francophones/Agricultures. Volume 14, Numéro 1, 71-75, janvier-février 2005. Nas regiões tropicais, principalmente no Cerrado brasileiro, para assegurar uma produção agrícola sustentável, é preciso recorrer a novos sistemas de cultura. Por isso, foi desenvolvido o Sistema de Plantio Direto com Cobertura Vegetal (SPDCV), que preconiza o não-revolvimento do solo e o cultivo de plantas de cobertura, antes ou depois da cultura comercial, para produzir mais biomassa e proteger permanentemente o solo. Desde 1999, vários estudos vêm sendo realizados no âmbito de um projeto de pesquisa franco-brasileiro. O principal objetivo foi quantificar os efeitos do SPDCV sobre a dinâmica da água, do nitrogênio e do carbono no perfil do solo. Os resultados permitiram confirmar que o uso desse sistema diminui significativamente o escoamento superficial e a erosão hídrica do solo. Nele, a oferta global de nitrogênio para a cultura comercial é maior. Além do mais, a planta de cobertura pode aproveitar a água e o nitrogênio não utilizados pela planta comercial para produzir mais biomassa, restituindo nutrientes para a próxima cultura comercial. Considerando as importantes restituições de biomassa proporcionadas por esse novo sistema a várias espécies cultivadas por ano, o SPDCV resultou em um balanço positivo de carbono e no aumento da taxa de matéria orgânica do solo. Termos para indexação: plantas de coberturas, reciclagem, utilização de biomassa, matéria orgânica, modelagem.