Effect of eucalyptus (Eucalyptus camaldulensis) and maize (Zea mays) litter on growth, development, mycorrhizal colonization and roots nodulation of Arachis hypogaea

In Senegal, farmers often cultivate groundnut in association with eucalyptus plantations to increase their incomes. However eucalyptus plantations produce large amounts of litter, which impact on groundnut has not been clearly elucidated yet. In order to investigate litter accumulation effect on growth, development, and groundnut root infection by arbuscular mycorrhizal fungi (AMF) and rhizobia, a greenhouse experiment was performed. The effect of eucalyptus litter was compared to that maize litter effect at three litter amendments (0, 1 and 5%). Chemical analysis showed that eucalyptus litter differed essentially from maize litter by its high polyphenols content and lower pH. At high amendment (5%), root nodulation and mycorrhizal colonization were significantly reduced with eucalyptus litter whereas no significant differences were observed with maize litter. In addition, groundnut growth, number of flowers per plant, pods yield and leaf mineral contents (N and C) were significantly lower for plant grown in soil highly amended with eucalyptus litter. Plants showed deficiency of chlorophyll content in leaves and were less vigorous compared to treatments without amendment and those amended at 1% level. For all parameters measured, plants grown in soil lowly amended (1%) and plants grown in control treatment did not significantly differ.Key words: Litter, Eucalyptus, Arachis hypogaea, Mycorrhizal symbiosis, Rhizobia

Effets d’application sur le long terme de fertilisants organiques et minéraux sur l’agrégation et les activités microbiennes d’un sol tropical sableux au Burkina Faso

Objectif: L’objectif a été d’étudier l’effet d’une application sur le long terme d’intrants organiques et minéraux sur la formation d’agrégats stables et les activités microbiennes d’un sol tropical sableux du Burkina Faso.Méthodologie et résultats: Ce travail a été réalisé dans l’observatoire de longue durée de la station agronomique de Saria au Burkina Faso. Dans cet essai, les parcelles en monoculture de sorgho (Sorghum bicolor) ont été soumises à des apports ou non d’intrants organiques (Fumier à 10 t ha-1 an-1 et Paille 83 t. ha-1 an-1) et minéraux (Urée à 60 kg N. ha-1 an-1) pendant 27 années. Les teneurs en C, N et P, les agrégats formés, le potentiel de respiration du sol, les activités de la chitinase et la longueur des hyphes fongiques ont été déterminés. Les résultats ont montré que l’apport sur le long terme des résidus organiques entraine une augmentation de la quantité des macro-agrégats (> 2000 μm) comparé au sol témoin. Cependant, cette augmentation ne dépend pas de la qualité des résidus organiques. Les résultats montrent que les macro-agrégats > 2000 μm sont corrélés aux hyphes fongiques, mais pas à l’activité chitinase. L’apport de N minéral exogène entraine une diminution de la macro-agrégation qui résulterait d’une complexation des polyphénols, agents agrégeants dans le processus d’agrégation pour le long terme.Conclusion et application des résultats: Cette étude à long terme confirme nos premiers résultats obtenu sur le cours terme et qui stipulent que la formation des macro-agrégats ne dépend pas de la qualité de résidus organiques. La mesure des hyphes fongiques semble plus déterminante dans la formation des macro-agrégats à long terme, par opposition aux activités fongiques dans le court terme.Mots clés: résidus organiques, N minéral, agrégation, activités fongiques, LixisolEnglish Title: Long-term effect of organic residues and mineral fertilizers on soil aggregation and microbial activities in a tropical sandy soil in Burkina FasoEnglish AbstractObjective: The objective was to study the effect of the long-term application of organic amendments and inorganic fertilizers on the formation and stability of soil aggregates and microbial activities in a tropical sandy soil in Saria (Burkina Faso). The relationships between aggregation, microbial activities and the amendments were discussed.Methodology and results: This study was performed in a long-term (27 years) experimental field in Saria (Burkina Faso) with a continuous sorghum (Sorghum bicolor) cropping system. A randomized block experiment comprising organic amendment (unamended control, straw at 83 t ha−1, manure at 10 t ha−1) coupled with mineral (no urea, urea at 60 kg ha−1) was sampled. Chemical parameters (C, N and P), the formation of aggregates, C mineralization, fungal hyphae length, and chitinase activity were measured in soil. The results showed that there were more macroaggregates (>2000 μm) in soils amended withresidues. However, the formation of macro-aggregates was not significantly affected by the quality of residues. The results showed that the macro-aggregates were correlated to fungal hyphae, but not to chitinase activity. The addition of exogenous mineral N reduced the macro-aggregation that would result from complexation of polyphenols that have been considered to be a primary factor in the aggregation process for the long-term experiment.Conclusions and application of the results: This long-term study confirms our previous results obtained on the short term incubation of soil amended with residues which showed that the formation of macroaggregates was not affected by the quality of residues. The measurement of fungal hyphae seems to be the most pertinent indicator associated with aggregation in a long-term experiment, as opposed to fungal activity in the short-term experiment.Keywords: residue quality, mineral N, aggregation, fungal activity, lixiso

Does cropping modify the decomposition function and the diversity of the soil microbial community of tropical fallow soil ?

This study considers the relationship between microbial diversity and soil organic decomposition function of two soils whose microbial diversity was first established using molecular biology (DGGE) and in situ catabolic potential (ISCP). The soil used was a tropical ferruginous Oxisol, with samples taken from a 21-year fallow and a plot that had been Cultivated for 4 years after lying fallow for 17 years. The samples from the 0-10 cm soil layer were incubated with or without the addition of Faidherbia albida litter under laboratory conditions (28 degrees C, 100% WHC) for 240 h. During incubation, the microorganism activity was measured (CO2, mineral N, phosphatase, beta-glucosidase and urease). In the unamended soil, the activity of the microorganisms was greater in the fallow soil which had a greater microbial diversity than that in the cultivated soil. However, other soil properties (carbon and organic nitrogen content, total microbial biomass) may also explain this result. For the amended soil, only the first 8 h of incubation showed a difference between the fallow and cultivated soil. During this period, the CO2 respiration in the fallow soil was higher than that recorded in the cultivated soil. This difference should be compared with the catabolic microbial diversity, which was higher in the fallow soil than in the cultivated soil. After this initial phase, the microbial community in the cultivated soil seemed to acquire similar functions to those in the fallow soil. The phosphatase and beta-glucosidase activities of the amended soils were higher in the fallow soil. This difference was maintained for the whole incubation period. The redundancy of microbial functions is discussed. (C) 2005 Elsevier B.V. All rights reserved

Effect of eucalyptus (Eucalyptus camaldulensis) and maize (Zea mays) litter on growth, development, mycorrhizal colonization and roots nodulation of Arachis hypogaea

In Senegal, farmers often cultivate groundnut in association with eucalyptus plantations to increase their incomes. However eucalyptus plantations produce large amounts of litter, which impact on groundnut has not been clearly elucidated yet. In order to investigate litter accumulation effect on growth, development, and groundnut root infection by arbuscular mycorrhizal fungi (AMF) and rhizobia, a greenhouse experiment was performed. The effect of eucalyptus litter was compared to that maize litter effect at three litter amendments (0, 1 and 5%). Chemical analysis showed that eucalyptus litter differed essentially from maize litter by its high polyphenols content and lower pH. At high amendment (5%), root nodulation and mycorrhizal colonization were significantly reduced with eucalyptus litter whereas no significant differences were observed with maize litter. In addition, groundnut growth, number of flowers per plant, pods yield and leaf mineral contents (N and C) were significantly lower for plant grown in soil highly amended with eucalyptus litter. Plants showed deficiency of chlorophyll content in leaves and were less vigorous compared to treatments without amendment and those amended at 1% level. For all parameters measured, plants grown in soil lowly amended (1%) and plants grown in control treatment did not significantly differ.Key words: Litter, Eucalyptus, Arachis hypogaea, Mycorrhizal symbiosis, Rhizobia

Amélioration de la productivité agricole des systèmes irrigués dans la zone Nord des Niayes

Trabajo presentado en la 3ème édition de la Conférence Intensification Durable (CID), celebrada en Dakar del 24 al 26 de noviembre de 2021

Barriers and Strategies to Boost Soil Carbon Sequestration in Agriculture

International audienceThe Paris Agreement calls for limiting global warming below 2°C. The “4 per 1,000 Initiative: Soils for food security and climate” was launched in 2015 to increase soil organic carbon sequestration with three objectives: mitigation of climate change, adaptation to climate change and improved food security. One of the challenges of the Initiative relates to its feasibility in contrasted biophysical, social and economic environments, questioning the adoption rate of required new practices. We conducted participatory multi-stakeholder workshops in France and Senegal to collect knowledge and perception of farmers, NGOs, agro-industries, administrations, donors and researchers on barriers and coping strategies for 4 per 1,000 innovations. Results in both countries reveal the predominance of social and economic barriers such as lack of knowledge or training, increased difficulties of fieldwork, workload, risk handling, funding and social pressure. Biophysical constraints such as limited potential of soil organic matter storage or rainfall scarcity and variability appear more important in Senegal. Identified actions to foster the sequestration of soil carbon call for an improved policy context leading to innovations in land planning, stakeholder communication, demonstration facilities, capacity building or financial support. Fewer constraints and coping strategies mention technical issues, showing that fostering agricultural soil carbon sequestration is more a question of enabling environment than technical innovations or farmers' willingness for change. We conclude that actions to support the 4 per 1,000 Initiative need to include a variety of stakeholders such as extension services, private sector, civil society, local institutions, policy makers, consumers, and not only farmers