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.

Under the humid tropical climate of the Brazilian cerrados, new cropping systems have become necessary to ensure sustainable agricultural production. Direct-sowing mulch-based cropping systems (DMC) introduce a cover crop before or just after the commercial crop. They help farmers enhance natural resources and produce more total biomass during the year. Crop residues protect the soil and increase organic restitution to the system. In 1999, a Franco-Brazilian collaborative project began scientific studies aimed at quantifying the impact of DMC, especially on the dynamics of water, carbon and nitrogen. DMC systems significantly decrease water runoff. In this way they effectively fight against soil erosion, even if additional infiltrated water can sometimes saturate the system and escape by drainage. The cover crop can then recycle some of that drainage loss and protect and use water resources better throughout the year. DMC systems also provide more favourable conditions that ensure the more intensive and more regular mineralisation of soil organic matter during the rainy season. Some of the organic mulch mineralises at the same time, providing the commercial crop with the benefit of a higher pool of inorganic nitrogen. The additional cover crop can recycle part of the nitrogen not used by the commercial crop and some of the nitrogen mineralised before or after this commercial cycle. Under DMC high microbial activity is responsible for higher CO2 emissions to the atmosphere, but the soil carbon balance is nonetheless positive because of the large biomass production and organic input from the introduction of the cover crop. Even under the hot and humid conditions of the cerrados, soil carbon content increases under the more productive DMC systems

Impactos do sistema de plantio direto com cobertura vegetal (SPDCV) sobre a dinâmica da água, do nitrogênio mineral e do carbono do solo do cerrado brasileiro.

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, 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

Valorisation du bois de pin d'Alep par déroulage : optimisation de son étuvage = Optimisation of steaming prior to rotary peeling of Aleppo pine

L'Algérie connaît un dynamisme démographique qui conduit à un plan de construction de logements très ambitieux. Le bois de construction est majoritairement importé d'Europe, alors que, parmi les ressources locales, les huit cent mille hectares de pin d'Alep algérien peuvent offrir une substitution partielle des matériaux bois importés. Des produits d'ingénierie bois d'intérêt pour la filière construction algérienne, le contreplaqué et le Lvl seraient potentiellement en bonne place. Ces deux produits sont issus du déroulage et, dans le cadre d'un projet Tassili qui vise la caractérisation et la valorisation du bois de pin d'Alep algérien, des essais exploratoires ont été menés pour déterminer les paramètres de déroulage ad hoc pour cette essence. Ce premier article traite de la préparation hygrothermique préalable du bois avant déroulage en prenant en compte quatre familles d'indicateurs pour déterminer une température d'étuvage qui soit un bon compromis. Ces indicateurs concernent : la propagation des fentes de recouvrance à coeur ; le désenrésinement du bois lors de l'étuvage ; la répartition d'eau dans le bois, facteur déterminant pour une prédiction de la durée d'étuvage ; l'évolution des efforts de déroulage en fonction de la température du bois. Une température de traitement de 50 °C apparaît être un bon compromis, à l'instar de celui utilisé dans le cas du pin maritim

Upland rice production under conservation agriculture cropping systems in cold conditions of tropical highlands

International audienceIn response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems based on conservation agriculture have been recommended to halt loss of soil fertility. To assess the yield performances of these cropping systems, an experiment was set up in 2003 at Andranomanelatra (1640 m asl) in the Malagasy highlands. Grain yield, yield components, biomass accumulation and nitrogen uptake of upland rice were analyzed in the 2004-2005, 2006-2006, and 2006-2007 seasons, and root length density was measured in the 2007-2008 season. The rice crop was planted every second year following two different crops: maize intercropped with soybean (M + S, with both conventional tillage and no tillage) and maize intercropped with Brachiaria ruziziensis (M + B only with no tillage). For each cropping system, two levels of fertilization were used: no fertilizer or application of organic inputs and mineral fertilizer. The season, cropping system, and fertilization treatment had significant effects on rice grain yields. Higher yields were associated with a greater number of plants per m2, which decreased significantly over the three seasons, probably due to the highly variable beginning of the rains, and in the final season, with attacks by soil insects. The rice yield with conventional tillage was the highest and differed significantly from rice yield when maize was intercropped with Brachiaria under the no-till system, but not when the maize was intercropped with soybean with no tillage. In all three seasons, grain yields were closely linked to crop N at harvest. Differences in N uptake between treatments appeared very early in the crop cycle. Under conventional tillage, root length density at 68 days after sowing was higher between 0 and 30 cm depth than with no tillage. In these cold highlands conditions, plant establishment appeared to be more difficult with no tillage and resulted in reduced plant development and plant N uptake, particularly when rice was planted after maize intercropped with Brachiaria

Identification of the main constraints for upland rice crop in direct-seeding mulch-based cropping systems under the high altitude conditions of the Madagascar highlands

International audienceIn the Madagascar highlands, increasing demand for rice combined with increasing land pressure in the lowlands led to the development of upland rice. To tackle the sustainability problem of upland crop production systems, Centre de coopération internationale en recherche agronomique pour le développement (CIRAD, an international governmental organization) and TAFA (an NGO) have developed direct-seeding mulch-based cropping systems (DMC), which not only decrease soil erosion but also increase soil fertility. To understand the mechanisms underlying the performance of upland rice DMC, an experiment was set up in 2003. The yield components of upland rice were studied under high-altitudinal conditions during six rainy seasons from 2003/04 to 2008/09. Treatments compared were two soil management techniques: conventional tillage with removal of most of the crop residues, associated with plowing ('plowing'); and a no-till system with direct seeding under mulch made of crop residues ('no-till'). The rice yields obtained were often better from plowing than from no- till, except in the last season. This difference was due to blast disease, which was significantly lower in no-till with low fertilization (best percentage of full grains and better weight of grain). The differences in yields obtained between no-till and plowing were mainly explained by problems of crop installation. The plant densities and plant growth were lower in no-till. This was particularly linked to slower root development in no- till. Overall, the biomass production of rotations of rice seemed too low in the highland conditions (low temperature) for the no-till system to be successful in the early years (low soil protection and slower restructuring of the soil)