Aggregate C depletion by plowing and its restoration by diverse biomass-C inputs under no-till in sub-tropical and tropical regions of Brazil

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Encapsulation of soil organic carbon (SOC) within aggregates is one of the principal mechanisms for long-term C sequestration, macroaggregate formation and stabilization. Our objectives were to quantify the changes in aggregate size distribution, aggregate-C concentrations and stocks upon conversion of native vegetation (NV) to conventional plow-based tillage (CT), and to assess the rate of aggregation and SOC recovery with no-till (NT) under diverse biomass-C inputs. The study was conducted at both sub-tropical (Ponta Grossa – PG, State of Parana´ ) and tropical (Lucas do Rio Verde – LRV, State of Mato Grosso) sites in Brazil. The SOC content under NV was used as a baseline to evaluate the depletion rate under CT and the restoration rate under NT. A speci?c emphasis was given to the largest macroaggregate size class (8– 19 mm) because of its importance to protecting the recently deposited labile SOC. A discriminant analysis of principal components (DAPC) indicated that NV soil is modi?ed by conversion to an arable land use and that, mechanical tillage, biomass input, and their interactions drastically in?uence the distribution of aggregate-size classes, aggregation indices, and SOC distribution within aggregates. At both sites, soil aggregation indices were positively impacted by NT and associated with SOC concentration in the labile fractions (e.g., total polysaccharides (TPS), hot water extractable organic C (HWEOC), particulate organic C (POC)). At the PG site, the 8–19 mm aggregate size fraction was signi?cantly affected by land use and tillage treatments and represented 54%, 43%, and 72%, under NV, CT, and NT in 0–20 cm depth, respectively. Furthermore, the 8–19 mm size fraction stored 55%, 45%, and 71% of the total SOC stock under NV (53.8 Mg C ha-1), CT (28.5 Mg C ha-1) and NT (51.2 Mg C ha-1), respectively. At the LRV site, the 8–19 mm aggregate size fraction decreased from 50% under Cerrado NV to 35% under CT, and ranged from 33% to 51% under diverse biomass-C input under NT in 0–20 cm depth. The 8–19 mm size fraction stored 52%, 37%, and 41% of the total SOC stock across all aggregate sizes under NV (25.4 Mg C ha-1), CT (11.7 Mg C ha-1), and NT (9.9–18.1 Mg C ha-1), respectively. The difference in SOC stock among land uses is largely attributed to storage in the 8–19 mm aggregate size class, indicating that NT cropping systems rebuilt the largest macroaggregates, which are crucial for stabilization of SOC.

Mots-clés : séquestration de carbone, MOS, gestion du sol, fertilité, scv

Outils de gestion des matières organiques en agriculture de conservation en Tunisie

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L’Agriculture de Conservation (AC) en Tunisie soumise à un climat semi-aride doit pouvoir, optimiser l’efficience des ressources en eau (400 mm/an) pour sécuriser la production de céréales et de fourrages. À court terme les techniques d’AC en améliorant les propriétés physiques du sol en surface par rapport aux système s traditionnels (Nouiri et al., 2008), permettent une meilleure infiltration de l’eau avec des quantités de résidus limitées.

Mots-clés : MOS, TCS - Techniques culturales simplifiées, mulch, Bilan hydrique, scv

Auto-Toxicity of Barley Residues in Direct Sowing

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TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high. Three phenolic acids (POH, SYR, PCO) were found to be involved significantly in the expression of barley auto-toxicity. The most present phenolic acid (VAN) in barley plant tissue did not show an individual significant role in barley auto-toxicity, suggesting rather a synergetic effect with one or more implicated phenolic acids. Also, the less frequent phenolic acid (FER) was the sole involved with CL/RL ratio, suggesting that its effect is a differential allocation of dry matter in favor of barley shoot growth. ‘Rihane’ was the sole barley variety of which TP content was significantly correlated to barley auto-toxicity27/11/2014TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high.

Mots-clés : orge, allélopathie, Adventices

Preliminary studies of pest constraints to cotton seedlings in a direct seeding mulch-based system in Cameroon

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The present study evaluated the pest constraints of an innovative crop management system in Cameroon involving conservation tillage and direct seedingmulch-based strategies.We hypothesized that the presence of mulch (i) would support a higher density of phytophagous arthropods particularly millipedes as well as pathogenic fungi that cause severe damage to cotton seedlings and (ii) would reduce early aphid infestations.The impact of two cover-crop mulches Calopogonium mucunoides and Brachiaria ruziziensis on the vigour of seedling cotton stands and arthropod damage was assessed in two independent field experiments conducted in 2001 and 2002 respectively. In both experiments the presence ofmulch negatively affected cotton seedling stand - by 13-14 % compared to non-mulched plots and the proportion of damaged seedlings was higher in mulched than in non-mulched plots supporting the hypothesis that mulch favoured soil pest damage. In both experiments insecticidal seed dressing increased the seedling stand and the number of dead millipedes collected and fungicide had little or no effect on seedling stand and vigour. It was however observed in 2002 that the fungicide seed dressing had a positive effect on seedling stand in non-mulched plots but not in mulched plots suggesting that fungi may have been naturally inhibited by B. ruziziensis mulch. The dynamics of aphid colonization was not influenced by the presence of mulch. In 2001 taller seedlings were found in mulched than non-mulched plots probably due to greater water and nutrient availability in C. mucunoides -mulched plots than in non-mulched plots.

Mots-clés : Légumineuses, brachiaria, ravageurs, Pesticides, mulch, Coton

Eco-intensification dans les montagnes du Vietnam - Contraintes à l'adoption de la culture sur couvertures végétales - Ecological intensification inn the mountains of Vietnam: Constraints to the adoption of cropping systems based on mulches and cover crop

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D’importants efforts sont menés dans le monde tropical pour l’érosion des sols et d’améliorer les bilans minéraux et hydriques. En agriculture familiale, l’adoption des SCV reste cependant limitée par les profonds changements que ces systèmes induisent dans la gestion des ressources de l’exploitation. L’objectif de cette étude menée au Vietnam est d’évaluer la faisabilité, pour différents types d’exploitations, de SCV préalablement mis au point à l’échelle de la parcelle. La méthode repose sur la simulation de ménages rationnels optimisant l’usage des ressources en vue d’objectifs de sécurité alimentaire et de revenu. Elle révèle la faible attractivité économique des SCV proposés en raison du surcroît de travail et d’intrants que ces nouveaux systèmes requièrent la première année de mise en oeuvre. L’étude montre aussi que pour rendre les SCV plus attractifs, il serait nécessaire de combiner des adaptations de la technique, telles que la diminution des quantités de biomasse dans les paillis associée à un recours aux herbicides, avec des subventions. Des recherches complémentaires sont nécessaires pour mieux quantififier les services environnementaux qui justififieraient de telles subventions. Il est également nécessaire de comprendre les causes de variations spatiales et temporelles des performances agronomiques et économiques des SCV et des systèmes actuellement pratiqués. Enfin, il faudrait comparer les SCV à d’autres techniques de conservation des sols, dont en particulier la culture en terrasse qui se répand actuellement dans la région.

Mots-clés : Agriculture de conservation, mulch, petite agriculture familiale, plante de couverture, scv, Socio-économie

Improvement of cropping systems by integration of rice breeding: a novel genetic improvement strategy

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Rice improvement is based to an increasing extent on ever-sharper genetic analysis to the detriment of classical breeding, which is disappearing. Analytical genetics are very promising, but they cannot replace integrated and Wnalized breeding. Little attention has been paid to improving participatory rice breeding methods for subsequent integration into sustainable cropping systems. Special methodological initiatives are required to ensure the success of this breeding-agronomy integration. This integration of inexpensive breeding methods has increased the biodiversity of rice: low temperature and drought tolerant upland rice varieties for mountain areas, and polyvalent varieties, which have the ability to grow in both rainfed or irrigated conditions, they are perfectly adapted to improved cropping systems and to beneWciaries’ needs and preferences. These preliminary results on this integration demonstrate that the present approach is relevant.

Mots-clés : Riz, écosystèmes cultivés, méthodologie, amélioration variétale

Dossier Séquestration Carbone

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La gestion de la matière organique (M.O.), renouvelable chaque année et au moindre coût, est au coeur de la construction agro-économique des systèmes de culture durables en semis direct (SCV), dans lesquels les outils biologiques ont remplacé les outils mécaniques. En zone tropicale humide (ZTH), où les conditions de minéralisation de la M.O. sont plus élevées que partout ailleurs sur la planète, l'introduction et la maîtrise de biomasses très puissantes «de renfort» ou «pompes biologiques» comme intercultures dans les rotations et successions annuelles, se sont avérées incontournables pour bâtir une agriculture durable performante et diversifiée en semis direct continu sur couverture permanente du sol...

Mots-clés : scv, MOS, propriétés physico-chimiques du sol, séquestration de carbone, TCS - Techniques culturales simplifiées, écosystèmes cultivés, recherche-action, méthodologie, diffusion, Socio-économie

Four-year experimentation on cereals under direct seeding mulch-based cropping system (DMC) by north Cameroonian farmers

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About 250 farmers have tried comparing cereal cultivation under direct seeding mulch-based cropping systems (DMC) against the traditional cropping practices from year 2001 to 2004. The on-farm tested systems include mixed cropping of a cereal (maize, sorghum, millet) and a cover crop (mucuna, brachiaria, crotalaria, cowpea, dolichos). These mixed cropping practices are done for the following objectives: 1) Produce aboveground biomass to build-up mulch for the following season's crop (mainly cotton). 2) Soil improvement through the physical and chemical (produce N) contribution of the associated plants. 3) Forage production. 4) Weed control. 5) Protect the soil surface against erosion and rain impact. 6) Produce consumable grains for man and animals. Up till present the tested plants meet the above objectives differentially and are adapted to the local agro climatic conditions of North Cameroon (rainfall from 700 to 1200 mm). Thus Brachiaria ruzisiensis produces aboveground biomass in quantities (4-5 t/ha even under mixed cropping) and quality (persisting as mulch for over one year after production). Further, it is very efficient in controlling Striga and is a good forage crop. However, it can impoverish the soils if its biomass is exported several times without any fertiliser supplements since it is not a nitrogen fixing plant. On the contrary Crotalaria retusa is a nitrogen fixing plant and therefore enriching the soils. This plant is less palatable to animals and therefore advantageous to farmers who cannot protect their farmland from pasturing animals in the dry season. It is equally very efficient in controlling weeds. Four years of experimentation has enabled us to produce practical recommendations in mixed cropping on the following : sowing date, crop type, tolerance to herbicides, competition with cereals, etc. This experimentation has also enabled us to see how the various plants tie with the above-mentioned objectives. On-going research work is on the following: 1) Diversifying the range of plant material available, focusing on local varieties. 2) Extending these cropping techniques to cover vertisols covering tens of thousands of hectares in North Cameroon. 3) Introducing these plants at the beginning and at the end of the cycle of the main crop in order to better use early and the late rains.

Mots-clés : maïs, Agriculture de conservation, Légumineuses, brachiaria, Adventices, scv, biomasse

Une approche socio-éco-territoriale en appui à la diffusion des techniques agroécologiques au Lac Alaotra, Madagascar

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A Madagascar, la saturation et la stagnation de la productivité des zones irriguées conduisent à une mise en culture de plus en plus fréquente et importante des bassins versants. Cependant l'érosion et le ruissellement peuvent engendrer la dégradation de ces sols fragiles et causer des dégâts sur les infrastructures et les rendements en aval. Le développement de solutions adaptées aux conditions locales qui soient économiquement rentables et facilement applicables, tout en préservant l'environnement, est un enjeu capital pour le pays. Les techniques agro-écologiques de « semis direct sur couverture végétale permanente » ou SCV peuvent relever ce défi. La région du Lac Alaotra a connu ces dernières campagnes le plus fort niveau de diffusion des techniques agro-écologiques dans le pays. Plus encore que le nombre d'adoptants ou la superficie concernée, la taille croissante des parcelles en SCV au sein des exploitations attestent d'un impact significatif en termes économiques (augmentation de la productivité, intégration au marché, accroissement des revenus). Plusieurs raisons peuvent expliquer cette évolution locale. Tout d'abord les résultats d'une recherche-développement performante, une large gamme de systèmes de culture adaptables aux diverses conditions agro-écologiques et catégories d'agriculteurs ayant été mis au point par l'ONG TAFA. Ensuite le rôle important que joue le soutien d'un projet d'aménagement et de développement local, le projet BVAlaotra. Son originalité est d'adopter une démarche globale et intégrée à dominante socio-éco-territoriale qui apporte des réponses sur mesure au système de contraintes auquel font face les paysans et exerce un effet de levier sur l'adoption.

Mots-clés : foncier, aménagement du territoire, érosion, Lac Alaotra, gestion du sol, scv

Labour biologique contre labour mécanique : comparaison de leurs effets sur la structure du sol au Nord Cameroun

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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.

Mots-clés : Climat, eau, sorgho, brachiaria, TCS - Techniques culturales simplifiées, propriétés physico-chimiques du sol, gestion du sol, scv, Coton
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