Search

espanolEl programa de investigacion del CGIAR sobre Cambio Climatico, Agricultura y Seguridad Alimentaria, desarrollado en colaboracion con varios socios, esta evaluando una serie de intervenciones para hacer frente a la amenaza de condiciones climaticas cambiantes sobre comunidades de pequenos ganaderos residentes junto a llanuras aluviales de rios, agrupadas bajo el nombre de “Aldeas Climaticamente Inteligentes” (ACI). Presentamos las caracteristicas de las granjas de las ACI en relacion a la produccion de los pequenos rumiantes y el contexto para un programa de seleccion y mejora. La informacion se obtuvo mediante la participacion en el proceso de investigacion de 140 hogares de 7 ACI en la cuenca del rio Nyando, en Kenya. Si bien la mayoria de los hogares eran liderados por hombres, se dio una mayor proporcion de mujeres adultas dentro de las comunidades. Los niveles de alfabetizacion fueron moderados. El 58 por ciento de la poblacion poseia menos de una hectarea de tierra para cultivar y para criar, de media, 6.96 ± 3.35 Unidades de Ganado Tropical, entre las cuales se incluian diferentes especies de animales. En los hogares dirigidos por mujeres, predominaban las ovejas, las cuales resultaban principalmente de cruces entre razas locales inespecificas, frente a las cabras, que eran mayoritariamente del tipo racial Cabra Pequena de Africa Oriental. Los apareamientos de los pequenos rumiantes se realizaban de manera aleatoria, sin ningun control de la endogamia, dado que los rebanos se mezclaban en los pastos y en los puntos de agua. Los ganaderos deseaban tener animales grandes y resistentes para poder beneficiarse de mejores precios de mercado. Sin embargo, las velocidades de crecimiento fueron bajas. Los rebanos de pequenos rumiantes eran dinamicos, con un 31 por ciento de los animales entrando y saliendo de los rebanos cada ano. Se podria implementar en las ACI un programa de mejora comunitario que emplease de manera optima los recursos disponibles y que incorporase la cuestion del genero en las tecnologias innovadoras. Este programa deberia acompanarse de un refuerzo de las capacidades para el desarrollo de la ganaderia, la mejora del estado sanitario y la comercializacion de los productos. Palabras clave: pequenos rumiantes, aldeas climaticamente inteligentes, practicas de manejo EnglishThe CGIAR research programme on Climate Change Agriculture and Food Security, in collaboration with several partners is testing a portfolio of interventions to address the threat of changing climatic conditions for smallholder farming communities living beside river flood plains, grouped into “Climate Smart Villages” (CSVs). We present characteristics of farms in CSV in relation to small ruminant (SR) production and the scenario for a breeding and improvement programme. Information was collated using participatory systems research methods from 140 households in seven CSVs in Nyando basin, Kenya. Although most households were headed by men, there were a higher proportion of adult women within the communities, and literacy levels were moderate. A total of 58 percent of the population owned Keywords: climate smart villages, management practices, small ruminants francaisLe programme de recherche du CGIAR sur le Changement Climatique, l’Agriculture et la Securite Alimentaire, developpe en collaboration avec divers partenaires, a evalue une serie d’interventions pour s’attaquer a la menace de conditions climatiques changeantes pesant sur les communautes de petits eleveurs habitant pres de plaines alluviales fluviales, groupees sous le nom de “Villages Intelligents face au Climat” (VIC). Nous presentons les caracteristiques des exploitations des VIC par rapport aux performances des petits ruminants et le contexte pour un programme de selection et d’amelioration. Les informations ont ete obtenues en impliquant 140 menages de 7 VIC du bassin du fleuve Nyando, au Kenya, dans le processus de recherche. Bien que la plupart des menages etaient diriges par des hommes, la proportion de femmes adultes dans les communautes a ete plus elevee. Les niveaux d’alphabetisation ont ete moderes. Le 58 pour cent de la population possedait moins d’un hectare de terre pour les cultures et pour elever, en moyenne, 6.96 ± 3.35 Unites de Betail Tropical de differentes especes d’animaux. Dans les menages diriges par des femmes, il y avait plus de moutons, resultant essentiellement du croisement de races locales non specifiques, que de chevres, celles-ci etant principalement du type racial Petite Chevre d’Afrique de l’Est. Les accouplements des petits ruminants se faisaient de facon aleatoire, sans aucun controle de la consanguinite, puisque les troupeaux se melangeaient dans les pâturages et aux points d’eau. Les eleveurs souhaitaient avoir des animaux grands et resistants pour pouvoir beneficier de meilleurs prix sur le marche. Cependant, les vitesses de croissance ont ete basses. Les troupeaux de petits ruminants ont ete dynamiques, avec un 31 pour cent des animaux entrant et quittant les troupeaux chaque annee. Un programme communautaire de selection employant les ressources disponibles de facon optimale et integrant le sujet du genre dans les technologies innovantes pourrait etre mis en œuvre dans les VIC. Ce programme devrait s’accompagner d’un renforcement des capacites pour le developpement de l’elevage, l’amelioration de l’etat sanitaire et la commercialisation des produits. Mots-cles: petits ruminants, villages intelligents face au climat, pratiques d’elevage

There is limited documentation of soil and water management technologies that enhance adaptation to climate change in drylands of Kenya. Rainfall patterns were analyzed in the semi-arid Machakos and Makueni counties of eastern Kenya using historical data. A total of forty-three smallholder farmers implementing soil water management practices were sampled, and an estimate of the seasonal water budget for current crop and livestock production systems computed. Analysis of rainfall amounts and distribution shows increasing variability, with the average annual total amounts decreasing over the past 50 years. Furthermore, the number of rainy days within the March-April-May season that can support crop growth is gradually decreasing. These decreases are however not significant at P

Increasing weather risks threaten agricultural production systems and food security across the world. Maintaining agricultural growth while minimizing climate shocks is crucial to building a resilient food production system and meeting developmental goals in vulnerable countries. Experts have proposed several technological, institutional, and policy interventions to help farmers adapt to current and future weather variability and to mitigate greenhouse gas (GHG) emissions. This paper presents the climate-smart village (CSV) approach as a means of performing agricultural research for development that robustly tests technological and institutional options for dealing with climatic variability and climate change in agriculture using participatory methods. It aims to scale up and scale out the appropriate options and draw out lessons for policy makers from local to global levels. The approach incorporates evaluation of climate-smart technologies, practices, services, and processes relevant to local climatic risk management and identifies opportunities for maximizing adaptation gains from synergies across different interventions and recognizing potential maladaptation and trade-offs. It ensures that these are aligned with local knowledge and link into development plans. This paper describes early results in Asia, Africa, and Latin America to illustrate different examples of the CSV approach in diverse agroecological settings. Results from initial studies indicate that the CSV approach has a high potential for scaling out promising climate-smart agricultural technologies, practices, and services. Climate analog studies indicate that the lessons learned at the CSV sites would be relevant to adaptation planning in a large part of global agricultural land even under scenarios of climate change. Key barriers and opportunities for further work are also discussed.

In Uganda, Ghana and Bangladesh, participatory tools were used for a socio-economic and gender analysis of three topics: climate-smart agriculture (CSA), climate analogue approaches, and climate and weather forecasting. Policy and programme-relevant results were obtained. Smallholders are changing agricultural practices due to observations of climatic and environmental change. Women appear to be less adaptive because of financial or resource constraints, because of male domination in receiving information and extension services and because available adaptation strategies tend to create higher labour loads for women. The climate analogue approach (identifying places resembling your future climate so as to identify potential adaptations) is a promising tool for increasing farmer-to-farmer learning, where a high degree of climatic variability means that analogue villages that have successfully adopted new CSA practices exist nearby. Institutional issues related to forecast production limit their credibility ...

Smallholder farmers in East Africa need information and knowledge on appropriate climate-smart agriculture (CSA) practices, technologies, and institutional innovations in order to effectively adapt to changing climatic conditions and cope with climate variability. This paper assesses farmer adoption of climate-smart agricultural practices and innovation after being exposed to Farms of the Future Approach (FotF). First; we explore and assess the various CSA technologies and practices; including institutional innovations farmers are adopting. Second; we identify and document farmer learning and dissemination pathways that can enhance adoption of CSA technologies and practices. Third; we identify existing institutions that enhance adoption of CSA practices. We use household survey data, complemented by qualitative information from focus group discussions and key informant interviews. The results show farmers are adopting a variety of CSA technologies, practices, and institutional innovations to after participating in the FotF approach with use of improved crop varieties, agroforestry, and scientific weather forecast information cited as the main practices. To minimize their risks and reduce vulnerabilities, farmers are diversifying and integrating five to 10 CSA practices in one season. Matengo pits, SACCOs, and efficient energy stoves were adopted by very few farmers due to their high initial investment costs and unsuitability to the area. Ninety-eight percent of farmers reported that they receive agricultural information orally from a variety of sources including government extension workers, seed companies, researchers, traditional experts, neighbors, radio agricultural shows, religious groups, farmer groups, and family members. Lastly, farmers reported that the FotF approach is a useful tool that enabled them to interact with other farmers and learn new CSA practices and innovations. Suggested improvements to make on the FotF included include longer trip duration, increased number of farmer participants, and gender balance and age considerations to include youth.

The changing climate is a threat to the smallholder farmers. Poverty and limited livelihood options increase vulnerability to climate risks. To counter this, a partnership between research and development organizations and the Nyando rural community developed Climate-Smart Villages (CSVs) model to test local actions that ensure food security, promote adaptation and build resilience to climatic stresses. The purpose of the study was to explore the changes in farming practices made by households which are arising from the partnership. The study made use of household-level surveys for five years (2011–2015). The findings show increased use of terracing to conserve soil and water, intercropping, use of improved crop varieties, and households adopting three or more new crop types, greatly expanding on-farm choices for resilient varieties. The results can be used to showcase crop production practices suitable for adapting to the changing climate in rural communities.

The private sector plays the most important role in financing agricultural investments, innovation and information dissemination where constraints on government investment render private sector actions more important. In East Africa, little is known about the participation of small businesses, independent traders, farmer organizations, large-scale wholesalers, marketing boards and cooperatives in climate-smart agriculture (CSA) and their potential role in its diffusion to small-scale farmers. In particular, the informal sector is out of view even though it forms the backbone of rural agrarian economies. This study examines relationships between private sector actors and farmers and examines supply chains of agricultural inputs, as well as agricultural product value chains. The potential for using the Quality Declared Seed (QDS) system to disseminate CSA bean and potato varieties is assessed, as is the commercial maize seed supply chain and its impact on agrobiodiversity. Finally, farmer trust of private sector actors, traders in particular, is evaluated. The data used is from a survey of 100 farmers and semi-structured interviews with traders, local input suppliers, transporters and marketing organizations.

Soil represents the largest reservoir of terrestrial organic C, and plays a critical role in global C cycling. In light of predicted climate change and a more unified approach to mitigate greenhouse gas emissions, the soil's ability to sequester C, and thus to act as a sink or a source for atmospheric CO2 has received growing interest. Organomineral assemblages are a unique niche in C cycling, with large capacity for storing anthropogenic C. However, the underlying biogeochemical mechanisms for C sequestration through organomineral associations are not yet well understood. One of the major challenges to study C sequestration in organomineral assemblages is lack of non-invasive analytical tools with a potential to obtain molecular-level information about the interactions between C and mineral components in submicron geochemical environments. In the present study, we have effectively employed synchrotron-based STXM–NEXAFS spectroscopy to access the K- and L-edges of biogeochemically relevant elements (C, N, Ca, Fe, Al, Si) to identify and image micro- and nano-C sequestration environments, and conduct submicron-level investigation of the compositional chemistry and other interactive features of C and minerals present in these hotspots using ultrathin section of intact organomineral assemblage. The C K-edge NEXAFS spectromicroscopy micrographs clearly demonstrated the existence of spatially distinct seemingly terminal micro- and nano-C repository zones, where organic C was sequestered in apparent agglomeration in the investigated organomineral assemblage. These submicron-C repository environments were only a few micrometers apart from each other; yet they were considerably different compositionally from each other. The organic C in the first repository environment was pyrogenic in origin, largely composed of quinone, phenols, ketones and aromatic ring structures. However, the second hotspot was dominated by filament-like structure, with striking similarity to the C 1s NEXAFS spectral signatures of organic C isolated from soil fungal and bacteria, and dominated by resonances from aliphatic-C and CN bonds of imidazol structures, carboxyl/carbonyl-C, amide- and O-alkyl-C functionalities. The composition of organic C in the organomineral interface around the strand-like structure was highly complex and composed of polysaccharides, amino sugars, amino acids, nucleic acids, and phospholipid fatty acid structures with polar and non-polar termini. The chemistry of mineral matter in the organomineral interface was also equally complex, ranging from Ca, Fe and Al ions, Fe and Al oxides, hydroxides and oxyhydroxides to phyllosilicates, which could provide a variety of polyvalent cations, hydroxyl surface functional groups and edge sites that can attract and bind microbial biomolecules. Based on the enormous complexity of the organic C functionalities and the coexistence of various inorganic components in the organomineral interface, it is possible to suggest that no single binding mechanism could be accountable for the organic C stored in the investigated submicron-C repository environment. Our results seem to suggest that the apparent C sequestration in the micro- and nano-C repository environment appear to be the cumulative result of physical protection and heterogeneous binding mechanisms ranging from ion exchange, hydrogen bonding, and hydrophobic bonding on silicate clay–organic complexes to adsorption on external and internal surfaces of clay minerals.

Black C is an essential component of the terrestrial C pool and its formation is often credited as a CO2 sink by transferring the fast-cycling C from the atmosphere–biosphere system into slower cycling C in the geosphere. This study is the first multi-element K- (C, N, Ca, Fe, Al and Si) soft-X-ray STXM–NEXAFS investigation conducted at a submicron-scale spatial resolution specifically targeting black C and its interaction with the mineral and non-black C organic matter in the organomineral assemblage. The STXM–NEXAFS micrographs and spectra demonstrated that pyrogenic C was dominated by quinoide, aromatic, phenol, ketone, alcohol, carboxylic and hydroxylated- and ether-linked C species. There was also evidence for the presence of pyridinic, pyridonic, pyrrolic, amine and nitril N functionalities. The non-black C organic matter contained amino acids, amino sugars, nucleic acids and polysaccharides known to exhibit negatively charged carboxylic, phenolic, enolic, thiolate and phosphate functionalities highly reactive towards metal ions and black C. The metal-rich mineral matrix was composed of phyllosilicate clay minerals, Fe and Al hydroxypolycations, oxides, hydroxides and oxyhydroxide that can attract and bind organic biopolymers. STXM–NEXAFS provided evidence for interactive association between pyrogenic C, non-black C organic matter and the mineral oxide and oxyhydroxide communities in the organomineral interface. These intimate associations occurred through a “two-way” direct linkage between black C and the mineral or non-black C organic matter or via a “three-way” indirect association where non-black C organic matter could serve as a molecular cross-linking agent binding black C with the mineral matrix or vice versa where inorganic oxides, hydroxides and polycations could act as a bridge to bind black C with non-black C organic matter. The binding and sequestration of black C in the investigated micro- and nano-C repository environments seem to be the combined action of physical entrapment in seemingly terminal biotic exclusion zone through the action of metal oxides and organic matter induced microaggregation and through molecular-level association ranging from ligand exchange, polyvalent cation bridging to weak hydrophobic interactions including van der Waals and H-bonding.

To achieve food security for many in low-income and middle-income countries for whom this is already a challenge, especially with the additional complications of climate change, will require early investment to support smallholder farming systems and the associated food systems that supply poor consumers. We need both local and global policy-linked research to accelerate sharing of lessons on institutions, practices and technologies for adaptation and mitigation. This strategy paper briefly outlines how the Research Program on Climate Change, Agriculture and Food Security (CCAFS) of the Consortium of International Agricultural Research Centres (CGIAR) is working across research disciplines, organisational mandates, and spatial and temporal levels to assist immediate and longer-term policy actions.

Loss of agroecosystem soil functions due to soil quality (SQ) degradation impacts Africa's agricultural viability and food security. Primary forest and farm fields deforested between 1930 and 2000 were sampled along a chronosequence on two parent materials in western Kenya. Two traditional long-term management systems were sampled: continuous low-input maize (Zea mays; Co), and kitchen garden (Ki) polyculture with organic inputs. Physical, biological, and chemical SQ indicators were measured. Degradation in Co followed exponential decay trends for most indicators (organic matter, active C, water-stable aggregates, available water capacity, electrical conductivity, CEC, pH, Ca, Mg and Zn), as well as for yield. Organic matter quality declined linearly, suggesting degradation will continue. For both parent materials and most indicators degradation of 25–93% below initial values resulted, but with ≤40% further drop below initial values and for more indicators under Co than Ki. P, Zn and possibly K accumulated over time under Ki. The extent of degradation was influenced by parent material. In conclusion, a basic accessible set of SQ indicators was successfully used to describe soil degradation dynamics under cultivation. Results suggest that regular organic inputs can significantly reduce degradation, especially of nutrient retention and soil structure, after forest conversion.

When building soil organic matter (SOM) contents in agricultural production systems, stabilization of both pre-existing as well as added C is important. A laboratory mineralization experiment was conducted over 374 days to evaluate the effect of pre-existing SOM on soil C mineralization after addition of organic matter (OM) using sugar cane. The SOM gradient used here stretched from 21 to 106 g C kg −1 soil and was a result of different periods of continuous cultivation of 5, 20, 35 and 105 years in comparison to a forest soil. The rate of organic C mineralization was found to be dependent on the status of pre-existing soil organic C (SOC). Highly degraded soil which had been under continuous cultivation for 35 years and more showed the highest rate of C mineralization per unit SOC (117.9 mg C g −1 C) while forest soil had the lowest amount of C mineralized per unit SOC (73.5 mg C g −1 C). Forest soil had the highest amount of increased C mineralization as a result of organic matter (OM) additions (8.0 mg C g −1 soil) followed by the highly degraded soil that had been under cultivation for 105 years (5.5 mg C g −1 soil). Additional mineralized C as a function of time after forest conversion declined progressively within the first 20 years of continuous soil use. Soil which had been under continuous cultivation for 20 years had the lowest amount of additional mineralized C (4.0 mg C g −1 soil). SOM stabilization efficiency in the studied soils appears to be highest with intermediate cultivation history of about 20 years. These soils that have been recently converted to cultivation also appear to have a greater ability to stabilize added OM than the most degraded soils investigated in this study. It is thus advisable to provide intervention strategies to reverse SOM decline for farming communities at an intermediate stage before the soils are highly depleted of SOC.

Soil degradation is one of the most serious threats to sustainable crop production in many tropical agroecosystems where extensification rather than intensification of agriculture has occurred. In the highlands of western Kenya, we investigated soil nitrogen (N) and phosphorus (P) constraints to maize productivity across a cultivation chronosequence in which land-use history ranged from recent conversion from primary forest to 100 years in continuous cropping. Nutrient treatments included a range of N and P fertilizer rates applied separately and in combination. Maize productivity without fertilizer was used as a proxy measure for indigenous soil fertility (ISF). Soil pools of mineral nitrogen, strongly bound P and plant-available P decreased by 82%, 31% and 36%, and P adsorption capacity increased by 51% after 100 years of continuous cultivation. For the long rainy season (LR), grain yield without fertilizer declined rapidly as cultivation age increased from 0 to 25 years and then gradually declined to a yield of 1.6Mgha � 1 , which was maintained as time under cultivation increased from 60 to 100 years. LR grain yield in the old conversions was only 24% of the average young conversion grain yield (6.4Mgha � 1 ). Application of either N or P alone significantly increased grain yield in both the LR and short rainy (SR) seasons, but only application of 120kgNha � 1 on the old conversion increased yield by 41Mgha � 1 . In both SR and LR, there was a greater average yield increment response to N and P when applied together (ranging from 1 to 3.8Mgha � 1 for the LR), with the greatest responses on the old conversions. The benefit‐cost ratio (BCR) for applying 120kgNha � 1 alone was o1 except on the old conversions, while BCRs were41 for applying 25kgPha � 1 alone at all levels of conversion for both seasons. Application of both N (120kgNha � 1 ) and P (25kgPha � 1 ) on the old conversions resulted in the greatest BCRs. This study clearly indicates that maize productivity responses to N and P fertilizer are significantly affected by the age of cultivation and its influence on ISF, but that loss of productivity can be restored rapidly when these limiting nutrients are applied. Management strategies should consider ISF and economic factors to determine optimal N and P input requirements for achieving and sustaining profitable crop production on degraded soils.

Black carbon (BC) is a quantitatively important C pool in the global C cycle due to its relative recalcitrance compared with other C pools. However, mechanisms of BC oxidation and accompanying molecular changes are largely unknown. In this study, the long-term dynamics in quality and quantity of BC were investigated in cultivated soil using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) techniques. BC particles and changes in BC stocks were obtained from soil collected in fields that were cleared from forest by fire at 8 different times in the past (2, 3, 5, 20, 30, 50, 80 and 100 years before sampling) in western Kenya. BC contents rapidly decreased from 12.7 to 3.8 mg C g−1 soil during the first 30 years following deposition, after which they slowly decreased to a steady state at 3.5 mg C g−1 soil. BC-derived C losses from the top 0.1 m over 100 years were estimated at 6,000 kg C ha−1. The initial rapid changes in BC stocks resulted in a mean residence time of only around 8.3 years, which was likely a function of both decomposition as well as transport processes. The molecular properties of BC changed more rapidly on surfaces than in the interior of BC particles and more rapidly during the first 30 years than during the following 70 years. The Oc/C ratios (Oc is O bound to C) and carbonyl groups (C=O) increased over the first 10 and 30 years by 133 and 192%, respectively, indicating oxidation was an important process controlling BC quality. Al, Si, polysaccharides, and to a lesser extent Fe were found on BC particle surfaces within the first few years after BC deposition to soil. The protection by physical and chemical stabilization was apparently sufficient to not only minimize decomposition below detection between 30 and 100 years after deposition, but also physical export by erosion and vertical transport below 0.1 m.

At nanometre scales, organic matter forms in soil are spatially, rather than chemically, complex, according to X-ray spectromicroscopy studies of thin sections of entire and intact free microaggregates. Organic matter forms detected at this spatial scale have no similarity to organic carbon forms of total soil. Organic matter in soil has been suggested to be composed of a complex mixture of identifiable biopolymers1 rather than a chemically complex humic material2. Despite the importance of the spatial arrangement of organic matter forms in soil3, its characterization has been hampered by the lack of a method for analysis at fine scales. X-ray spectromicroscopy has enabled the identification of spatial variability of organic matter forms, but was limited to extracted soil particles4 and individual micropores within aggregates5,6. Here, we use synchrotron-based near-edge X-ray spectromicroscopy7 of thin sections of entire and intact free microaggregates6 to demonstrate that on spatial scales below 50 nm resolution, highly variable yet identifiable organic matter forms, such as plant or microbial biopolymers, can be found in soils at distinct locations of the mineral assemblage. Organic carbon forms detected at this spatial scale had no similarity to organic carbon forms of total soil. In contrast, we find that organic carbon forms of total soil were remarkably similar between soils from several temperate and tropical forests with very distinct vegetation composition and soil mineralogy. Spatial information on soil organic matter forms at the scale provided here could help to identify processes of organic matter cycling in soil, such as carbon stability or sequestration and responses to a changing climate.

Amazonian Dark Earths (ADE) are a unique type of soils developed through intense anthropogenic activities that transformed the original soils into Anthrosols throughout the Brazilian Amazon Basin. We conducted a comparative molecularlevel investigation of soil organic C (SOC) speciation in ADE (ages between 600 and 8700 years B.P.) and adjacent soils using ultraviolet photo-oxidation coupled with 13 C cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR), synchrotron-based Fourier transform infrared-attenuated total reflectance (Sr-FTIR-ATR) and C (1s) near edge X-ray absorption fine structure (NEXAFS) spectroscopy to obtain deeper insights into the structural chemistry and sources of refractory organic C compounds in ADE. Our results show that the functional group chemistry of SOC in ADE was considerably different from adjacent soils. The SOC in ADE was enriched with: (i) aromatic-C structures mostly from H- and C-substituted aryl-C, (ii) O-rich organic C forms from carboxylic-C, aldehyde-C, ketonic-C and quinine-C, and (iii) diverse group of refractory aliphatic-C moieties. The SOC in adjacent soils was predominantly composed of O-alkyl-C and methoxyl-C/N-alkyl-C structures and elements of labile aliphatic-C functionalities. Our study suggests that the inherent molecular structures of organic C due to selective accumulation of highly refractory aryl-C structures seems to be the key factor for the biochemical recalcitrance and stability of SOC in ADE. Anthropogenic enrichment with charred carbonaceous residues from biomass-derived black C (BC) is presumed to be the precursor of these recalcitrant polyaromatic structures. Our results also highlight the complementary role that might be played by organic C compounds composed of O-containing organic C moieties and aliphatic-C structures that persisted for millennia in these anthropic soils as additional or secondary sources of chemical recalcitrance of SOC in ADE. These organic C compounds could be the products of: (i) primary recalcitrant biomolecules from non-BC sources or (ii) secondary processes involving microbial mediated oxidative or extracellular neoformation reactions of SOC from BC and non-BC sources; and stabilized through physical inaccessibility to decomposers due to sorption onto the surface or into porous structures of BC particles, selective preservation or through intermolecular interactions involving clay and BC particles.

This study investigates the spatial distribution of organic carbon (C) in free stable microaggregates (20–250 μm; not encapsulated within macroaggregates) from one Inceptisol and two Oxisols in relation to current theories of the mechanisms of their formation. Two-dimensional micro- and nano-scale observations using synchrotron-based Fourier-transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy yielded maps of the distribution of C amounts and chemical forms. Carbon deposits were unevenly distributed within microaggregates and did not show any discernable gradients between interior and exterior of aggregates. Rather, C deposits appeared to be patchy within the microaggregates. In contrast to the random location of C, there were micron-scale patterns in the spatial distribution of aliphatic C–H (2922 cm−1), aromatic C=C and N–H (1589 cm−1) and polysaccharide C–O (1035 cm−1). Aliphatic C forms and the ratio of aliphatic C/aromatic C were positively correlated (r2 of 0.66–0.75 and 0.27–0.59, respectively) to the amount of O–H on kaolinite surfaces (3695 cm−1), pointing at a strong role for organo-mineral interactions in C stabilization within microaggregates and at a possible role for molecules containing aliphatic C-H groups in such interactions. This empirical relationship was supported by nanometer-scale observations using NEXAFS which showed that the organic matter in coatings on mineral surfaces had more aliphatic and carboxylic C with spectral characteristics resembling microbial metabolites than the organic matter of the entire microaggregate. Our observations thus support models of C stabilization in which the initially dominant process is adsorption of organics on mineral surfaces rather than occlusion of organic debris by adhering clay particles.

Anthropogenic perturbations have profoundly modified the Earth’s biogeochemical cycles, the most prominent of these changes being manifested by global carbon (C) cycling. We investigated long-term effects of human-induced land-use and land-cover changes from native tropical forest (Kenya) and subtropical grassland (South Africa) ecosystems to agriculture on the dynamics and structural composition of soil organic C (SOC) using elemental analysis and integrated 13 C nuclear magnetic resonance (NMR), near-edge X-ray absorption fine structure (NEXAFS) and synchrotron-based Fourier transform infrared-attenuated total reflectance (Sr-FTIR-ATR) spectroscopy. Anthropogenic interventions led to the depletion of 76%, 86% and 67% of the total SOC; and 77%, 85% and 66% of the N concentrations from the surface soils of Nandi, Kakamega and the South African sites, respectively, over a period of up to 100 years. Significant proportions of the total SOC (46‐73%) and N (37‐73%) losses occurred during the first 4 years of conversion indicating that these forest- and grassland-derived soils contain large amounts of labile soil organic matter (SOM), potentially vulnerable to degradation upon human-induced land-use and land-cover changes. Anthropogenic perturbations altered not only the C sink capacity of these soils, but also the functional group composition and dynamics of SOC with time, rendering structural composition of the resultant organic matter in the agricultural soils to be considerably different from the SOM under natural forest and grassland ecosystems. These molecular level compositional changes were manifested: (i) by the continued degradation of O-alkyl and acetal-C structures found in carbohydrate and holocellulose biomolecules, some labile aliphatic-C functionalities, (ii) by side-chain oxidation of phenylpropane units of lignin and (iii) by the continued aromatization and aliphatization of the humic fractions possibly through selective accumulation of recalcitrant H and C substituted aryl-C and aliphatic-C components such as (poly)-methylene units, respectively. These changes appeared as early as the fourth year after transition, and their intensity increased with duration of cultivation until a new quasi-equilibrium of SOC was approached at about 20 years after conversion. However, subtle but persistent changes in molecular structures of the resultant SOM continued long after (up to 100 years) a steady state for SOC was approached. These molecular level changes in the inherent structural composition of SOC may exert considerable influence on biogeochemical cycling of C and bioavailability of essential nutrients present in association with SOM, and may significantly affect the sustainability of agriculture as well as potentials of the soils to sequester C in these tropical and subtropical highland agroecosystems.

Methodological constraints limit the extent to which existing soil aggregationmodels explaincarbon(C) stabilization insoil. Wehypothesize that the physical infrastructure of microaggregates plays a major role in determining the chemistry of the occluded C and intimate associations between particulate C, chemically stabilized C and the soil mineral matrix. We employed synchrotron-based scanning transmission X-ray microscopy (STXM) coupled with near-edge X-ray absorption fine structure (C 1s-NEXAFS) spectroscopy to investigate the nanoscale physical assemblage and C chemistry of 150-mm microaggregates from a Kenyan Oxisol. Ultra-thin sections were obtained after embedding microaggregates in a sulfur block and sectioning on a cryo-microtome at 255C. Principal component and cluster analyses revealed four spatially distinct features: pore surfaces, mineral matter, organic matter, and their mixtures. The occurrence of these features did not vary between exterior and interior locations; however, the degree of oxidation decreased while the complexity and occurrence of aliphatic C forms increased from exterior to interior regions of the microaggregate. At both locations, compositional mapping rendered a nanoscale distribution of oxidized C clogging pores and coating pore cavities on mineral surface. Hydrophobic organic matter of aromatic and aliphatic nature, representing particulate C forms appeared physically occluded in 2- to 5-mm pore spaces. Our findings demonstrate that organic matter in microaggregates may be found as either oxidized C associated with mineral surfaces or aromatic and aliphatic C in particulate form. Using STXM and C 1s-NEXAFS we are for the first time able to resolve the nanoscale biogeocomplexity of unaltered soil microaggregates.

Black Carbon (BC) may significantly affect nutrient retention and play a key role in a wide range of biogeochemical processes in soils, especially for nutrient cycling. Anthrosols from the Brazilian Amazon (ages between 600 and 8700 yr BP) with high contents of biomassderived BC had greater potential cation exchange capacity (CEC measured at pH 7) per unit organic C than adjacent soils with low BC contents.Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy coupled with scanning transmission X-ray microscopy (STXM) techniques explained the source of the higher surface charge of BC compared with non-BC by mapping crosssectional areas of BC particles with diameters of 10 to 50 mm for C forms. The largest cross-sectional areas consisted of highly aromatic or only slightly oxidized organic C most likely originating from the BC itself with a characteristic peak at 286.1 eV, which could not be found in humic substance extracts, bacteria or fungi. Oxidation significantly increased from the core of BC particles to their surfaces as shown by the ratio of carboxyl-C/aromatic-C. Spotted and non-continuous distribution patterns of highly oxidized C functional groups with distinctly different chemical signatures on BC particle surfaces (peak shift at 286.1 eV to a higher energy of 286.7 eV) indicated that non-BC may be adsorbed on the surfaces of BC particles creating highly oxidized surface. As a consequence of both oxidation of the BC particles themselves and adsorption of organic matter to BC surfaces, the charge density (potential CEC per unit surface area) was greater in BC-rich Anthrosols than adjacent soils. Additionally, a high specific surface area was attributable to the presence of BC, which may contribute to the high CEC found in soils that are rich in BC.

Soil organic matter (SOM) is a fundamental component of soil and the global C cycle. We used C (1s) near-edge x-ray absorption fine structure (NEXAFS) and synchrotron-based Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy to speciate C and investigate the influence of land use on the composition of SOM in the humic substances extracted from clay and silt fractions. Soil samples were collected from natural forest, tea and Cupressus plantations and cultivated fields in Ethiopia. Carbon K-edge spectra revealed multiple C (1s) electron transitions in the fine structure of C NEXAFS region (284-290 eV) indicating the presence of aromatic-C, phenolic-C, aliphatic-C, carboxylic-C, and O-alkyl-C in the humic substances. It also exhibited good selectivity, where specific energy regions correspond to C in discrete functional groups. However, regions of slight overlap between 1s-3p/σ* transition of aliphatic-C and 1s-π* transition of carboxylic-C may not be excluded. Fourier transform infrared-attenuated total reflectance spectroscopy showed larger proportions of aromatic-C (25.5%, 21.9%) and asymmetric and symmetric aliphatic-C (19.7%, 15.2%) groups in the silt than in clay, respectively. However, smaller proportion of polysaccharides (19.3%, 11.5%) was obtained from the silt compared with clay. The proportions of phenols (20.7%, 20.4%), aliphatic deformation of CH 2 or CH 3 (13.1%, 14.5%), and carboxylic (9.8%, 8.3%) groups were of similar magnitude in both fractions. The proportion of polysaccharides decreased in the order: natural forests > plantations > cultivated fields, while recalcitrant aromatic-C increased in the order: natural forest < plantation < cultivation. Therefore, C (1s) NEXAFS and synchrotron-based FTIR-ATR spectroscopy are powerful, nondestructive techniques that can potentially be used not only to identify and fingerprint complex structural characteristics of organic C macromolecules but also to investigate the impact of long-term anthropogenic management on the composition and biogeochemical cycling of organic C in terrestrial ecosystems.

We present a framework for prioritizing adaptation approaches at a range of timeframes. The framework is illustrated by four case studies from developing countries, each with associated characterization of uncertainty. Two cases on near-term adaptation planning in Sri Lanka and on stakeholder scenario exercises in East Africa show how the relative utility of capacity vs. impact approaches to adaptation planning differ with level of uncertainty and associated lead time. An additional two cases demonstrate that it is possible to identify uncertainties that are relevant to decision making in specific timeframes and circumstances. The case on coffee in Latin America identifies altitudinal thresholds at which incremental vs. transformative adaptation pathways are robust options. The final case uses three crop–climate simulation studies to demonstrate how uncertainty can be characterized at different time horizons to discriminate where robust adaptation options are possible. We find that impact approaches, which use predictive models, are increasingly useful over longer lead times and at higher levels of greenhouse gas emissions. We also find that extreme events are important in determining predictability across a broad range of timescales. The results demonstrate the potential for robust knowledge and actions in the face of uncertainty.

We investigated speciation, oxidative state changes, and long- and short-term molecular-level dynamics of organic S after 365 d of aerobic incubation with and without the addition of sugarcane residue using XANES spectroscopy. Soil samples were collected from the upper 15 cm of undisturbed grasslands since 1880, from undisturbed grasslands since 1931, and from cultivated fields since 1880 in the western United States. We found three distinct groups of organosulfur compounds in these grassland-derived soils: (i) strongly reduced (S{sup 0} to S{sup 1+}) organic S that encompasses thiols, monosulfides, disulfides, polysulfides, and thiophenes; (ii) organic S in intermediate oxidation (S{sup 2+} to S{sup 5+}) states, which include sulfoxides and sulfonates; and (iii) strongly oxidized (S{sup 6+}) organic S, which comprises ester-SO{sub 4}-S. The first two groups represent S directly linked to C and accounted for 80% of the total organic S detected by XANES from the undisturbed soils. Aerobic incubation without the addition of sugarcane residue led to a 21% decline in organanosulfur compounds directly linked to C and to up to an 82% increase inorganic S directly bonded to O. Among the C-bonded S compounds, low-valence thiols, sulfides, thiophenic S, and intermediate-valence sulfoxide S seem to be highly susceptible tomore » microbial attack and may represent the most reactive components of organic S pool in these grassland soils. Sulfonate S exhibited a much lower short-term reactivity. The incorporation of sugarcane residue resulted in an increase in organosulfur compounds directly bonded to C at the early stage of incubation. However, similar to soils incubated without residue addition, the proportion of organic S directly linked to C continued to decline with increasing duration of aerobic incubation, whereas the proportion of organic S directly bonded to O showed a steady rise.« less

The soil environment is a primary component of the global biogeochemical sulfur (S) cycle, acting as a source and sink of various S species and mediating oxidation state changes. However, ecological significance of the various S forms and the impacts of human intervention and climate on the amount and structural composition of these compounds are still poorly understood. We investigated the long-term influences of anthropogenically mediated transitions from natural to managed ecosystems on molecular-level speciation, biogeochemical dynamics, and the apparent temperature sensitivity of S moieties in temperate, subtropical, and tropical environments with mean annual temperature (MAT) ranging from 5 degrees C to 21 degrees C, using elemental analysis and X-ray absorption near-edge structure (XANES) spectroscopy. Land-use and land-cover changes led to the depletion of total soil S in all three ecoregions over a period of up to 103 years. The largest decline occurred from tropical forest agroecosystems (67% Kakamega and 76% Nandi, Kenya), compared to losses from temperate (36% at Lethbridge, Canada, and 40% at Pendleton, USA) and subtropical (48% at South Africa) grassland agroecosystems. The total S losses correlated significantly with MAT. Anthropogenic interventions profoundly altered the molecular-level composition and resulted in an apparent shift in oxidation states of organic S from native ecosystems composed primarily of S moieties in intermediate and highly reduced oxidation states toward managed agroecosystems dominated by organic S rich in strongly oxidized functionalities. The most prominent change occurred in thiols and sulfides, the proportion of which decreased by 46% (Lethbridge) and 57% (Pendleton) in temperate agroecosystems, by 46% in subtropical agroecosystems, and by 79% (Nandi) and 81% (Kakamega) in tropical agroecosystems. The proportion of organic S directly linked to O increased by 81%, 168%, 40%, 92%, and 85%, respectively. Among the various organic S functionalities, thiols and sulfides seem to have higher apparent temperature sensitivity, and thus these organic S moieties may become prone to losses due to land-use changes, even from the cooler regions of the world if MAT of these regions rise in the future.

In the highlands of Western Kenya, we investigated the reversibility of soil productivity decline with increasing length of continuous maize cultivation over 100 years (corresponding to decreasing soil organic carbon (SOC) and nutrient contents) using organic matter additions of differing quality and stability as a function of soil texture and inorganic nitrogen (N) additions. The ability of additions of labile organic matter (green and animal manure) to improve productivity primarily by enhanced nutrient availability was contrasted with the ability of stable organic matter (biochar and sawdust) to improve productivity by enhancing SOC. Maize productivity declined by 66% during the first 35 years of continuous cropping after forest clearing. Productivity remained at a low level of 3.0 t grain ha-1 across the chronosequence stretching up to 105 years of continuous cultivation despite full N–phosphorus (P)–potassium (K) fertilization (120–100–100 kg ha−1). Application of organic resources reversed the productivity decline by increasing yields by 57–167%, whereby responses to nutrient-rich green manure were 110% greater than those from nutrient-poor sawdust. Productivity at the most degraded sites (80–105 years since forest clearing) increased in response to green manure to a greater extent than the yields at the least degraded sites (5 years since forest clearing), both with full N–P–K fertilization. Biochar additions at the most degraded sites doubled maize yield (equaling responses to green manure additions in some instances) that were not fully explained by nutrient availability, suggesting improvement of factors other than plant nutrition. There was no detectable influence of texture (soils with either 11–14 or 45–49% clay) when low quality organic matter was applied (sawdust, biochar), whereas productivity was 8, 15, and 39% greater (P

Received 17 December 2004; accepted 3 January 2005; published 16 February 2005. [1] Small-scale heterogeneity of organic carbon (C) forms in soils is poorly quantified since appropriate analytical techniques were not available up to now. Specifically, tools for the identification of functional groups on the surface of micrometer-sized black C particles were not available up to now. Scanning Transmission X-ray Microscopy (STXM) using synchrotron radiation was used in conjunction with Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to investigate nano-scale distribution (50-nm resolution) of C forms in black C particles and compared to synchrotron-based FTIR spectroscopy. A new embedding technique was developed that did not build on a C-based embedding medium and did not pose the risk of heat damage to the sample. Elemental sulfur (S) was melted to 220� C until it polymerized and quenched with liquid N2 to obtain a very viscous plastic S in which the black C could be embedded until it hardened to a noncrystalline state and was ultrasectioned. Principal component and cluster analysis followed by singular value decomposition was able to resolve distinct areas in a black carbon particle. The core of the studied biomass-derived black C particles was highly aromatic even after thousands of years of exposure in soil and resembled the spectral characteristics of fresh charcoal. Surrounding this core and on the surface of the black C particle, however, much larger proportions of carboxylic and phenolic C forms were identified that were spatially and structurally distinct from the core of the particle. Cluster analysis provided evidence for both oxidation of the black C particle itself as well as adsorption of non-black C. NEXAFS spectroscopy has great potential to allow new insight into black C properties with important implications for biogeochemical cycles such as mineralization of black C in soils and sediments, and adsorption of C, nutrients, and pollutants as well as transport in the geosphere, hydrosphere, and atmosphere.

That farmers rely on the land for their livelihoods is obvious. The converse, that ecosystem services depend on farmers' behaviors, must also be recognized if agricultural productivity is to be improved. In sub Saharan Africa, the 70% of the population employed in the agricultural sector (Sanchez 2002) is engaged in an on-going 'dialogue' with the agricultural natural resource base. Recently, this conversation has not been going well: per capita food production has remained stagnant for the last 40 years so now 180 million on the continent lack adequate food, a number that has increased by 100% since 1970 (Sanchez 2002). To provide adequate diets to the African population, increases in crop yields of 3.0 to 3.5% y-1 are needed (Reardon et al. 2001), but such increases have not been realized as average maize yields have remained static at 1200 kg ha-1.