Effect of land use on the quantity of organic matter in different soils from the Lesser Antilles

The effect of different types of land use (banana or food crops vs pastured fallow or artificial meadow) on the quantity and the quality of soil carbon content was investigated on three types of soil of the Lesser Antilles (Andept, Ultisol, Vertisol). Organic carbon content of various particle size fractions of the 0- 10 cm layer of the Vertisol was determined by a physical soil fractionation method. Soil organic matter content depended upon land uses and soil types. For the Andept, banana crops led to a soil carbon status (0-40 cm) that was higher than that of pastured fallow (13.3 and 12.6 kg C.m2 respectively). In contrast, for the Ultisol and the Vertisol, organic matter content was lower under food crops than under pastured fallows or pastures, with a more pronounced variation for the vertisol. For this soil, the decrease of organic carbon content in the 0-10 cm layer was mainly due to a decrease in the 0-5 μm and >50 μm fractions identified as microbial metabolites and root exudates, and plant residues respectively. ----- L'effet compare des cultures bananieres ou marai'cheres et des jacheres paturees ou des prairies sur le stock de matiere organique est etudie pour trois types de sols (andosol, sol ferrallitique, vertisol) des Petites Antilles. La caracterisation par fractionnement granulometrique de la matiere organique de I'horizon 0-10 cm du vertisol est utilisee pour preciser la nature des variations du stock. Le stock de matiere organique depend du systeme de culture et du type de sol. Pour I'andosol, le statut organique est plus eleve sous bananes que sous jachere paturee. Au contraire, pour le sol ferrallitique et le vertisol, le stock de matiere organique de ces sols est plus faible sous cultures maraicheres que sous jachere paturee et prairie. L' effet depressif des cultures maraicheres sur le statut organique est le plus important sur le vertisol. Dans ce sol, la diminution du stock organique de I'horizon 0-10 cm est principalement due a la diminution des composes organiques d'origine microbienne, des exudats racinaires et des debris vegetaux

Impact of spatial heterogeneity created by the termite building activity (Cubitermes niokoloensis) on the activity and genetic structure of the denitrifying community

International audienc

Changes in nematode communities following cultivation of soils after fallow periods of different length

The composition of the nematofauna was studied in four soils that differed in length of fallow restoration period since previous cultivation. The longest fallow period was 21 years. Plots were sampled for 2 years after starting cultivation of the fallow soils. The treatments were ranked following a restoration-exploitation gradient depending on fallow duration and the number of years of millet cultivation after fallow clearing ; components of the nematofauna were analysed for correlation with this ranking. The nematode community structures at the first date of sampling during cultivation clearly reflected the length of the fallow period. Nematode community structures in the fallow soils rapidly approached those in the continuously cultivated soil ; they were hardly distinguishable during the second year of cultivation. One-third of the recorded nematode taxa exhibited pronounced responses to the cultivation. Mononchidae, Anatonchidae, Tylencholaimoidea, #Acrobeles, #Pseudacrobeles, Tylenchidae and #Helicotylenchus preferred sites of more mature successional status, while Dorylaimoidea, #Tylenchorhynchus and Rhabdolaimidae dominated the cultivated sites. The maturity index (MI) did not distinguish the management regimes. The plant parasite index (PPI) tended to decrease with higher restoration status linked to greater abundance of the Tylenchidae in these situations. The decrease of fungal to bacterial feeders reflected a decreasing importance of the fungal decomposition pathway after resuming cultivation. (Résumé d'auteur

Multi-criteria spatialization of soil organic carbon sequestration potential from agricultural intensification in Senegal

On the eve of the 15th climate negotiations conference in Copenhagen,the pressure to assess all climate mitigation options is mounting. In this study, abio-physic model and a socio-economic model were designed and coupled to assessthe carbon sequestration potential of agricultural intensification in Senegal. Thebiophysicalmodel is a multiple linear regression, calibrated and tested on a dataset oflong-term agricultural trials established in West Africa. The socio-economic modelintegrates both financial and environmental costs related to considered practicechanges. Both models are spatially explicit and the resulting spatial patterns werecomputed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65–0.83 MtC.With regards to local-scaled intensification as local projects, the most profitable areaswere identified in agricultural expansion regions (especially Casamance), while theareas that meet the current financial additionality criteria of the Clean DevelopmentMechanism were located in the northern part of the Peanut Basin. Using the currentrelevant mode of carbon valuation (Certified Emission Reductions), environmentalbenefits are small compared to financial benefits. This picture is radically changedif “avoided deforestation”, a likely consequence of agricultural intensification, isaccounted for as the greenhouse gases sink capacity of projects increases by anaverage of a hundred-fold over Senegal

Reconstitution des teneurs en carbone et de la population de vers de terre dans un vertisol sous prairie (Martinique)

International audienc

Realising the Carbon Benefits of Sustainable Land Management Practices: Guidelines for Estimation of Soil Organic Carbon in the Context of Land Degradation Neutrality Planning and Monitoring

Land degradation is one of the threats to human and natural systems. Fortunately, over the past few decades awareness of this challenge has grown, and 122 countries have committed to setting land degradation neutrality (LDN) targets, of which 84 have officially validated their targets, and 51 have put their targets into legislation. In this concept, LDN is achieved if new degradation is balanced by reversal of degradation elsewhere in the same land type by restoration or rehabilitation. The primary instrument for achieving LDN is through the implementation of sustainable land management (SLM) practices. Because of its multifunctional roles and its sensitivity to land management soil organic carbon (SOC) was selected as one of three indicators for LDN. Compared with the other global LDN indicators, that is, land cover change and land productivity dynamics (LPD) (measured as net primary productivity), SOC is challenging to manage and monitor at large scales. Moreover, SOC density in soils can vary greatly, even on the scale of meters, and fluctuates over time, for example between seasons. Comparative evaluation of SOC change between different SLM options (e.g. for land planning), tracking SOC dynamics through time (i.e. SOC monitoring) and effectively mapping SOC changes at large scales (e.g. for verifying LDN achievement) requires the combination of rigorous soil sampling schemes and the use of software tools/biophysical models for SOC assessment. To provide practical guidance to support the deployment of SLM interventions to maintain or enhance SOC stocks, for LDN and for other objectives such as landbased climate change adaption and/or mitigation a series of decision trees was developed, based on the latest available knowledge. This report reviews and compares available tools and models for SOC estimation. It presents practical guidance for land managers and puts forward policy-oriented proposals. Guidance for land managers emphasizes the selection of SLM practices to maintain or enhance soil organic carbon and achieve LDN. It addresses the choice of SLM practices suited to the local socio-economic and biophysical context; methods for measurement and monitoring of SOC; and the use of tools/ models for SOC assessment to estimate SOC and map SOC, and how to choose an appropriate tool/model according to the purpose. Policy-oriented options include to (i) share the guidance for land managers at the appropriate level; (ii) monitor SOC change as an indicator of SLM intervention to support assessment of LDN achievement in 2030; (iii) apply gender-responsive actions addressing gender-based differences and promote gender equality and women’s empowerment; (iv) design a framework for LDN Planning and means to support it

Sustainable land management contribution to successful land-based climate change adaptation and mitigation : a report of the Science-Policy Interface

Sustainable Land Management (SLM) represents a holistic approach to achieving long-term productive ecosystems by integrating biophysical, socio-cultural and economic needs and values. SLM is one of the main mechanisms to achieve Land Degradation Neutrality (LDN).To foster and facilitate the adoption of SLM practices that address DLDD while mitigating climate change and enhancing climate change adaptation, this report assesses the synergistic potential of SLM practices while also critically evaluating the possible trade-offs between the different objectives. The assessment provides a scientifically-sound basis to understand SLM's potential to contribute to multiple objectives, and provides practical guidance for creating an enabling environment for selection and large-scale implementation of effective, locallyadapted SLM practices. Overall objective : The objective of the present report is to "highlight the science-based synergistic potential of SLM practices to address DLDD, climate change mitigation and adaptation" as a contribution to the UNCCD's Science Policy Interface (SPI) work programme 2016-2017. By doing so, the linkages between SLM practices to address DLDD, climate change adaptation and mitigation, and resulting synergies and trade-offs, are considered