Fragile Soils Research Articles

Assessing soil properties and tidal behaviors as a strategy to avoid environmental degradation in developing new paddy fields in tidal areas

Fluviomarine areas are promising for development of new paddy fields if fragile soil properties, natural water logging and tidal behaviors receive strategic management to avoid environmental degradation. Three transects were established to investigate the complexity of sediment and tidal attributes. Soils were sampled from each horizon of profiles and key mineralogical and chemical properties analyzed. An upper fluvial derived zone was characterized by exchangeable Ca as the dominant cation (decreasing concentration with depth) and pyrite was absent. A lower zone derived from marine sediment was dominated by exchangeable Mg (increasing concentration with depth) accompanied by pyrite. The dominance and distribution of Ca and Mg indicate the origin of sediment in tidal areas. These acid sulfate soils have limited nutrient reserves being dominated by quartz in the sand fraction. The clay was dominated by kaolinite and illite and a variable proportion of vermiculite, resulting in variation of CEC values, being high with vermiculite. Pyrite position from soil surface varied from 25 to 100cm (mostly 50–60cm) depending on thickness of fluvial zone and local slope morphology. Significant variations in tidal amplitudes led to the separation of fluviomarine areas into neap-spring tide zone (NSZ), spring tide zone (SZ) and non-flooding tide zone (NZ). Zoning allowed the selection of the SZ with low tidal amplitude and NZ as being suitable for new paddy field development. A potential drop of soil pH from 5 to 2 may occur with serious consequences for paddy field and watercourses (huge acidity and dissolved metals at toxic levels) if pyrite is exposed to oxidation conditions (e.g. drainage system lowering water level below pyrite position). Water management through “controlled drainage” should be applied to avoid pyrite oxidation, soil degradation and poor water quality. This includes dimension (depth and width) of drainage canals and maintaining water levels above the pyrite zone through control using floodgates thereby ensuring pyrite zone remains under reducing conditions.

Ecology and management of forest soils

Forest soils have characteristic properties that set them apart from the usual types of soils used for growing crops. Often rocky, of poor quality, and in mountainous terrain, forest soils are nevertheless the foundation of the entire forest ecosystem, supporting a diverse assemblage of plants and animals. They are often fragile soils, easily subject to erosion by road building or logging operation. A proper understanding of forest soils is an essential component of understanding forest ecology and maintaining the diversity and productivity of forested land. This new edition emphasizes the ecological aspects of forest soils. It is global in its scope, discussing soil types ranging from the tropical rainforest soils of Latin America to the boreal forest soils of Siberia. Separate chapters discuss the physical, chemical, and biological aspects of forest soils, with additional chapters on soil organic matter, roots, and biogeochemistry. It highlights the site specific factors that are important in each case and discusses practical management aspects including: nutrition management, thinning, site preparation techniques, soils for nursery and seed orchard operation, problem soils, atmospheric deposition of nutrients, soil acidity, and techniques for sustaining and improving long term soil productivity.

Perspectives on the assumed causes of land degradation in the rangelands of Sub-Saharan Africa

Soil erosion and land degradation are serious problems in tropical Africa, especially Sub-Saharan Africa, where they are widely recognized as more serious problems than in non-tropical areas. Sub-Saharan Africa experiences deleterious levels of soil erosion, largely due to the interaction between harsh climates of high erosivity, fragile soils of high erodibility, steep slopes, and poor natural resource management. The fundamental challenge is to separate purely background-level soil erosion due to biophysical, geomorphic, topographic, and climatic conditions from what is caused by humans. This review shows that the human-induced causes of soil erosion and land degradation in Sub-Saharan Africa are not fully understood and some of the commonly listed causes may not always stand the test of critical scrutiny. The popular views of human-induced soil erosion and land degradation not only fail to take into consideration the fact that land degradation is primarily a physical process, but also they do injustice to adaptive ecosystem management by the local inhabitants. The review specifically questions the stereotypes of overpopulation, overgrazing, deforestation, overstocking, and general rangeland degradation due to human resource use in Sub-Saharan Africa. Empirical evidence suggests that biophysical factors including soil properties, climatic characteristics, topography, and vegetation can sometimes interact among themselves to yield high soil erosion and degradation rates independent of anthropogenic impacts.

Filiação entre arenitos da formação Guará e sua cobertura pedológica no Rio Grande Do Sul

As regiões oeste e sudoeste do Rio Grande do Sul, RS, destacam-se pela ocorrência de extensas áreas com solos frágeis desenvolvidos sobre sedimentos arenosos continentais do Mesozoico da Bacia do Paraná. O uso inadequado das terras tem acelerado o processo de arenização sobre essas áreas. Nesse caso, o conhecimento dos solos é fundamental para a seleção de práticas adequadas de manejo visando a sua sustentabilidade. Os objetivos deste trabalho foram entender a evolução e estabelecer a relação, em termos de filiação, entre a rocha e sua respectiva cobertura pedológica por meio de perfis desenvolvidos sobre os arenitos da Formação Guará no RS. Foram realizadas análises químicas, físicas, mineralógicas e morfológicas em dois perfis de Cambissolos Háplicos e um perfil de Argissolo Vermelho. Verificaram-se indícios de adição externa de materiais aos perfis estudados, principalmente ilmenita, oriunda da alteração de áreas com rochas vulcânicas básicas circunvizinhas. O aporte de material alóctone nos perfis estudados é responsável pela pedogênese de horizontes B com incremento de argila, característicos de Argissolos e Cambissolos. Os dados sugerem a identificação e interpretação de um sexto componente pedogenético definido como contexto geológico do entorno.

Clay minerals of late Pleistocene sites (Jonzac and Les Cottés, SW France): Applications of X-ray diffraction analyses to local paleoclimatic and paleoenvironmental reconstructions

The crystal-chemical properties of clay minerals are closely dependent on the physicochemical conditions prevailing at the time when they formed in soils and weathered zones. The degree of alteration of primary minerals and the composition of the secondary products are clearly linked to climate and plant cover. In particular, changes are rapid under temperate conditions which favor the development of thick soils, but slow in cold contexts favoring thin and fragile soils. In this paper, the mineral composition of two Pleistocene clay-rich deposits is investigated in order to contribute to reconstructing paleoenvironmental changes. Jonzac (Charentes, SW France) and Les Cottés (Vienne, SW France) are two rock-shelters with long archaeological sequences which include faunal remains and were recently radiometrically dated. The decomposition of XRD patterns at each site allows identification of the principal mineral phases and semi-quantitative estimation of their relative proportions. The variation of these proportions is analyzed through indexes based on the relative intensities of the decomposed bands. The clay fraction of both sites mostly results from the transformation of the minerals forming the sediments in the surrounding area of the rock-shelter terrace, including contributions from the hillside. Mineralogical clay data are compared with the faunal spectrum identified at both sites in order to discuss paleoenvironmental implications.At Jonzac, during the Quina Mousterian period dated to MIS4, the environment was cold and dry. The dominant mineralogical phases are inherited from the rocks (weak pedogenesis). This is consistent with the faunal analysis data typical of the MIS4. During the Mousterian of Acheulean Tradition period, dated to MIS3, the mineralogical composition of the clay deposits changed significantly, suggesting a less wet environment. The Aurignacian deposits dated to the end of MIS3/early MIS2 are rich in mixed layer minerals (MLMs) which are produced by the hydrolysis processes in soils. The climatic conditions probably became milder. However, because no faunal remains were found, this evolution is uncertain. The Les Cottés deposits, dated between MIS3 and early MIS2, are mineralogically typical of a cold environment where soil reactions are not very active. However, some weak variations of the indexes suggest temporary temperate conditions during the Les Cottés interstadial and in the Aurignacian. The parallelism between mineral signature and paleontological evidence in recording relatively rapid variations between contrasted climates suggests that clay mineral assemblages from rock-shelter deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at a local scale.

Development and the Yucatec Maya in Quintana Roo: some successes and failures

Maya agriculture is currently outperforming alternatives across the Yucatán Peninsula, while changing to incorporate new ideas that fit with its basic commitment to shifting agriculture based on maize as the staple and over 100 minor crops. Considerable research over the last 60 years has shown the reasons for agricultural resilience, which include thorough understanding of the Yucatán environment and use of a range of resources and techniques that allow fine-tuning in particular situations while remaining flexible overall. Development efforts have usually failed in this environment, which has shallow and fragile soils and suffers from frequent droughts, typhoons, and pest outbreaks. The predictor of development success is usually supply and demand: where there is a market, the Maya will work to develop supply capability; where there is no market, traditional subsistence methods are better than the introductions. Government or international help is, however, needed to help develop markets and to provide expert knowledge of how to mobilize for them and connect to them. When this has been done, some important successes have followed. A current problem is the international subsidy economy. Neoliberalism in the Maya context involves a reduction of government help to local and small-scale enterprises while large-scale multinational firms are given enormous direct and indirect subsidies by their home governments and by commodity-producing nations. The resulting unfair competition is a block on development. Actual free markets—in the sense of local grassroots enterprise being given something like a level playing field—could be an improvement.Key words: Maya; neoliberalism; Indigenous agricultural knowledge; access to markets

Pedological perspective of gully erosion sites within Kendu escarpment-Sondu Miriu Region, West Kenya

Gully erosion is a common feature in western Kenya, rendering large expanses of otherwise arable land uncultivable and uninhabitable. Gully erosion in the area was classified into two types: the Awach-type and the Sondu-type. The current study aimed at providing insight into physical and chemical properties of soil that promote soil erosion and determine the gully formation type. Field studies were conducted at 4 sites (3 eroded and 1 non- eroded). Physical (particle size distribution, structure stability, infiltration rate, dispersibility, and soil hardness), and chemical (pH, exchangeable cations, total-C, and total-N) properties of soil samples collected from the sites were analyzed in the laboratory. The results showed alkaline pH; high exchangeable sodium (Na) percentage (ESP); fragile soil structure; high dispersibility; and low infiltration rate are major factors contributing to the formation of Awach-type of gully. In contrast, impermeable top layer of hard crust and coarse-textured soil layers beneath it in addition to high ESP facilitated the formation of Sondu-type of gully. Soils of the eroded sites and the non-eroded sites differed mainly in the ESP, which influenced the soil structure stability, water infiltration rate, and soil dispersibility. Susceptibility of soil layers to erosion depended on the magnitude of ESP and sand content. Key words: Exchangeable sodium percentage, gully erosion, infiltration rate, Kenya, soil dispersion, soil structure

The effects of stubble retention and tillage practices on surface soil structure and hydraulic conductivity of a loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and stubble management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of stubble management (stubble retained vs. stubble removed) under contrasting tillage practices (no-tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) in Dingxi, Gansu, the northwestern Loess Plateau, China. Our results indicated that after 4 years small but significant changes in soil properties were observed amongst the different tillage and stubble treatments. Surface soil (0–5 cm) under no-tillage with stubble retention had the highest water stability of macroaggregates (>250 μm), soil organic carbon (SOC) and saturated hydraulic conductivity. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indicating the importance of the latter on soil structural stability. The improvement in soil structure and stability was confirmed by higher soil hydraulic conductivity measurements. Consistently higher K sat was detected in the no tillage with stubble retained soil compared to other treatments. Therefore, no-tillage with stubble retention practice is an effective management technique for improving physical quality of this fragile soil in the long term.

Variações nos teores de carbono orgânico em função do desmatamento e revegetação natural do solo

A flutuação no conteúdo de matéria orgânica do solo é severamente afetada pelo uso e manejo do solo. Em solos física e quimicamente frágeis a destruição da vegetação nativa pode levar a diminuição drástica do estoque de carbono. No entanto, solos jovens que apresentam alta resiliência, quando manejados adequadamente, podem recuperar facilmente os valores originais de carbono. O objetivo deste trabalho foi quantificar os teores de carbono orgânico de um Neossolo e um Chernossolo em decorrência de seu uso, em especial após o desmatamento e revegetação natural. Coletaram-se amostras de duas camadas (0-5 e 5-15 cm) em dois solos (Neossolo e Chernossolo) ocorrentes numa pequena bacia hidrográfica com relevo fortemente ondulado, com quatro condições de uso (mata nativa, lavoura nova, lavoura velha e revegetação com capoeira). Avaliaram-se a distribuição granulométrica, a densidade do solo e os teores de carbono orgânico. Os dados foram submetidos à análise estatística considerando um delineamento inteiramente casualizado, num esquema trifatorial (tipos de solos, tipos de usos e camadas amostradas). O estoque de carbono do solo diminuiu após o desmatamento para a inastalação de culturas anuais com baixa adição de resíduos e revolvimento intenso do solo. A revegetação natural das áreas degradadas pelo cultivo convencional recuperou rapidamente o estoque de carbono dos solos, mesmo permanecendo as impressões herdadas da erosão (menor teor de argila) e da aplicação de fertilizantes e corretivos (menor acidez potencial e maior disponibilidade de fósforo e potássio).

Rainfall Impacts Winter Wheat Seedling Emergence from Deep Planting Depths

Farmers in the low‐precipitation (<300 mm annual precipitation) region of the Pacific Northwest (PNW) practice a 2‐yr tillage‐based winter wheat (Triticum aestivum L.)–summer fallow (WW–SF) rotation. Winter wheat is planted deep into moisture in late August or early September and seedlings emerge through 10 to 16 cm of dry soil cover. Rain showers that occur after planting create fragile soil crusts that the emerging first leaf often cannot penetrate. A rainfall simulator was used to conduct a five‐factor factorial laboratory experiment to evaluate emergence of WW planted deep in pots. Factors were: (i) rainfall intensity and duration (1.25 mm/h for 3 h, and 2.50 mm/h for 2 h); (ii) timing of rainfall after planting (1, 3, and 5 d after planting + controls); (iii) cultivar (standard‐height vs. semi‐dwarf), (iv) residue on the soil surface (0, 840, and 1680 kg/ha); and (v) air temperature (21° and 30°C). The high‐intensity rain caused a 2.3‐fold reduction in emergence compared to the low‐intensity rain. Emergence improved proportionally with increasing quantities of surface residue. The standard‐height cultivar had four times greater emergence than the semi‐dwarf. Air temperature and timing of rainfall had no significant effect on WW emergence. Results show that planting a WW cultivar with long coleoptile and first leaf as well as maintaining high quantities of surface residue to intercept rain drops will enhance WW stand establishment after rain showers to benefit both farmers and the environment.

Innovation and productivity in dryland agriculture: a return-risk analysis for Australia

SUMMARYDespite a highly variable climate and fragile soils, dryland farming systems in Australia continue to be productive and viable. This review nominates the farming practices, and their development through investment in science and technology, that have helped sustain dryland farming systems in Australia. It sets the context for dryland agriculture in Australia and specifically examines the risks and returns from technological innovations over the past 30 years. It then examines possible sources of productivity gains in the next 20 years.Australian dryland farming systems have performed favourably compared to the agricultural sectors in most other countries over the past 30 years. Australian Research, Development and Extension (RD&E) has been a significant contributor to the realized agricultural productivity growth over this period. However, growth in the productivity of agriculture appears to have slowed down in the last 10 years: this is partly a result of extended dry conditions and declining growth in public investment in RD&E. It is reflected in slowing rates of technology adoption on broadacre farms and changes in investment confidence of farm owners.Future productivity gains will require continued strong investment in RD&E to meet current and emerging challenges. Future technologies and policies will help improve productivity by removing inefficiencies, increasing the efficiency of resource use and developing breakthrough innovations.As evidenced by Australia's success in productivity growth, meeting the global challenge to produce more food in the future will depend partly on investments in RD&E, risk management systems, farmer skill and human capital and policies that encourage efficiency gains.

Quantifying effects of different agricultural land uses on soil microbial biomass and activity in Brazilian biomes: inferences to improve soil quality

Maintenance of soil quality is a key component of agriculture sustainability and a main goal of most farmers, environmentalists and government policymakers. However, as there are no parameters or methods to evaluate soil quality directly, some attributes of relevant soil functions are taken as indicators; lately, an increase in the use of soil microbial parameters has occurred, and their viability as indicators of proper land use has been highlighted. In this study we performed a meta-analysis of the response ratios of several microbial and chemical parameters to soil disturbance by different land uses in the Brazilian biomes. The studies included native forests, pastures and perennial and annual cropping systems. The introduction of agricultural practices in all biomes covered previously with natural vegetation profoundly affected microbial biomass-C (MB-C)―with an overall decrease of 31%. Annual crops most severely reduced microbial biomass and soil organic C, with an average decrease of 53% in the MB-C. In addition, the MB-C/TSOC (total soil organic carbon) ratio was significantly decreased with the transformation of forests to perennial plantation (25%), pastures (26%), and annual cropping (20%). However, each biome reacted differently to soil disturbance, i.e., decreases in MB-C followed the order of Cerrado>Amazon>Caatinga>Atlantic Forest. In addition, the Cerrado appeared to have the most fragile soil ecosystem because of lower MB-C/TSOC and higher qCO2. Unfortunately, the Cerrado and the Amazon, demonstrated by our study as the most fragile biomes, have been subjected to the highest agronomic pressure. The results reported here may help to infer the best land-use strategies to improve soil quality and achieve agriculture sustainability. The approach can also be very useful to monitor soil quality in other tropical and subtropical biomes.

National policy of watershed management and flood mitigation after the 921 Chi-Chi earthquake in Taiwan

Registering a 7.3 magnitude on the Richter scale, the 921 Chi-Chi Earthquake that struck central Taiwan on September 21, 1999 left the island nation with fragile soils, frequent floods, and debris flow, further weakening homeland resources. Taiwan’s dense population had forced its residents to use mountain hills for agriculture and development. The 92-Flood in 2004, which incurred vast monetary losses and human casualties, caused the government to rethink its strategy for land use. In order to use land in a more efficient and in an eco-friendly manner, the Council for Economic Planning and Development, Executive Yuan of the Taiwanese government proposed the “Land Recovery Strategy and Action Plan” in 2006. Its core concept was aimed at “respecting, and adapting to, nature.” To achieve this goal, a hillside watershed management and flood mitigation policy was proposed. Factors of safety, economy, and ecology were included in the policy. Both strategies and practical measures to be implemented were organized in a chart for better understanding and for reference by other countries with similar conditions.

A potential geoconservation map of the Las Lagunas area, northern Peru

SUMMARYThe Andean páramo ecosystems host geodiversity of global importance, but also have important societal functions, including agricultural production and delivery of water to people and industry. Páramo geo-ecosystems are highly susceptible to environmental degradation because of their alpine relief, extreme climate and fragile soils. In contrast to other parts of the world, geodiversity assessment studies in the Andes are scarce. A geodiversity assessment method was adapted and used to produce a potential geoconservation map of the Andean páramo. The Las Lagunas area (Cajamarca, Northern Peru) has a rich archive of climate proxy data and landscape reconstruction, and plays a key role in the functioning of regional geo-ecosystems. Undisturbed proxies for climate change are contained in four Late-Glacial recessional complexes of its former local ice cap and in pollen records preserved in the post-glacial peat cover. These new findings were used to develop a refined chronostratigraphy of the Late-Glacial warming period in the Andes of Northern Peru. Geo-ecosystem functions (for example water and carbon storage) depend on the environmental vulnerability and disturbance of the landforms and deposits. Therefore, potential geoconservation areas that combine a high scientific value and environmental vulnerability with a low disturbance and low frequency of occurrence should be prioritized for geoconservation. Such a strategy should also optimize sustainable use of resources and development of these areas. Mountainous countries like Peru require future management strategies that recognize and incorporate potential geoconservation information in regional planning, to prevent unnecessary loss of irreplaceable soils, climate proxies and geo-ecosystem functions upon future changes in land use and climate.

A PERSPECTIVE ON THE AUSTRALIAN WALNUT INDUSTRY BY THE INDUSTRY DEVELOPMENT MANAGER

Australia is a large, dry continent with few major rivers and many fragile soils. To address these disadvantages, Australian researchers have found innovative ways to increase horticultural productivity and to protect the environment. Examples are the Tatura Soil Management System, Regulated Deficit Irrigation, Partial Rootzone Drying, Integrated Pest Management and the Tatura Trellis. On the positive side, many parts of Australia have large areas of available land, high levels of solar radiation, long growing seasons and few pests and diseases of walnuts (Juglans regia). Presently, Australia imports 96% of its annual consumption or around 8,500 tonnes of in-shell equivalent walnuts each year. The current production of Australian walnuts is around 500 tonnes but in the next 5 years this is expected to increase to over 10,000 tonnes. In the last decade, walnut plantings have risen sharply from 500 ha to around 3000 ha with orchards ranging in size from 1 ha to >700 ha. Victoria has an estimated 1600 ha, Tasmania 650 ha, New South Wales has over 1600 ha and the balance in South Australia and Western Australia. Following the success of the almond industry in Australia, walnuts offer farmers considerable scope for diversification from traditional crops and some relief from drought and water reform policies. This can be achieved by increased tree densities, soil management, intensive tree training, improved rootstocks/cultivars, efficient micro-irrigation, pest & disease management and mechanisation.

METODOLOGIA DE PLANEJAMENTO DE PAISAGENS FRAGMENTADAS VISANDO A FORMAÇÃO DE CORREDORES ECOLÓGICOS

Objetivou-se com este estudo definir uma metodologia de planejamento que possibilite a análise da estrutura de determinada paisagem e de suas características bióticas e abióticas, para a elaboração de um zoneamento adequado do uso do solo. As principais diretrizes do estudo foram a manutenção da estabilidade hídrica e o aumento da conectividade na microbacia, por meio da identificação de zonas de maior fragilidade ambiental, considerando a hidrografia, a geomorfologia, a pedologia e a distribuição dos fragmentos florestais remanescentes. A pesquisa de campo foi realizada com auxílio de imagens de satélite e fotografias aéreas em uma microbacia com 4.629,47 ha no entorno do Parque Nacional do Iguaçu, Terceiro Planalto Paranaense. Foram efetuados diferentes diagnósticos dos aspectos bióticos e abióticos, resultando em uma simulação do uso adequado do solo e no aumento da conectividade com a formação de corredor ecológico. A aplicabilidade do método foi demonstrada com a simulação de zonas para conservação e recuperação, que representaram 34,4% da área da microbacia nas zonas de menor potencial de utilização agropecuária, em função da fragilidade de seus solos. Os resultados demonstraram que ganhos ambientais significativos podem ser obtidos com a aplicação da metodologia, proporcionando o aumento da conectividade entre os fragmentos remanescentes. Palavras-chave: Fragmentação; ecologia de paisagens; conservação da biodiversidade. Abstract Methodology for planning fragmented landscapes aiming the creation of Ecological Corridors. The purpose of this study is to develop a planning methodology which makes analyses of the structure of a certain landscape possible, as well as its biotic and abiotic characteristics in order to elaborate an adequate land use planning. Moreover, the guidelines of this study were maintenance of hydric stability and increasing of connectivity in the watershed by identification of regions with great environmental fragility, considering hydrography, geomorphology, pedology, and remaining forest patches. In field survey, satellite image and aerial photographs were used. The watershed studied has 4,629.47 ha and is located near Iguaçu National Park on the third Paraná plateau. Several biotic and abiotic aspects were distinguished in order to simulate an adequate land use and to establish a biodiversity corridor. This method was validated by simulating conservation and recovery zones, which cover 34.4% of watershed area. Such zones represent low potential regarding crops and cattle raising due to their fragile soil. Results showed the applicability of the methodology used, reflecting environmental gains, providing the increasing of connectivity among remaining forest patches. Keywords: Fragmentation; landscape ecology; biodiversity conservation.

Upstream Petroleum Degradation of Mangroves and Intertidal Shores: The Niger Delta Experience

This article was inspired by a field reconnaissance survey of outcrops along the Nembe-Brass axis of the petroliferous Niger Delta. It reviews various tradeoffs of the impact of upstream petroleum (seismic and production) operations on the mangrove ecosystems in that region, the largest in Sub-Saharan Africa. Mangroves and intertidal shores are considered critical to the economic well-being of this region owing to the people's dual occupation in fishing and farming. The mangrove ecosystem provides a nutrient medium, which serves as a nursery and spawning ground for many fish species and other biota. Oil and gas activities might destroy these spawn areas, causing reduction in resource output and community pressure. Devegetation of the mangrove forest as a result of seismic delineation leaves the fragile soil exposed, unprotected, and susceptible to erosion. Again, loss of vegetation might discourage the natural role of plants in air purification (CO(2) utilization and O(2) production). The release of nutrients (organic N(2), NH(3), and NO$\rm{{_{3};{-}}}$) and polyaromatic hydrocarbons (PAHs) to the environment, with the attendant increase in microbial load, increases biochemical O(2) demand (BOD) and depletes dissolved O(2) (DO) in H(2)O to a level that is beyond the tolerance limit of organisms. This anoxic situation leads to asphyxiation and subsequent fish kill in affected areas. In order of increasing vulnerability, the mangroves and intertidal shores of the Niger Delta fall under categories 8 to 10 on the environmental sensitivity index (ESI) scale, which predisposes the areas to serious long-term effects and clean-up complexity. Thus, there is need to monitor mangrove systems and shoreline changes in the areas of considerable seismic and production activities, especially in the coastal Niger Delta, where pipeline corrosion due to salt intrusion into the swampy environment and 'unsighted fingers' of sabotage have increased the prevalence of oil spills.

Soil fertility restoration techniques in sub-Saharan Africa using organic resources

Food security concerns are currently escalating in sub-Saharan Africa (SSA) due to poor soil management practices on the fragile soils. This review describes the role of organic resources acting both as amendments and fertilizers in improving soil nutrient status and productivity potentials in SSA. The use of organic resources has achieved significant strides in improving soil fertility in many agro-ecological zones in SSA. Balanced fertilization of soils through synchronized supply of adequate nutrients to growing crops as well as increasing soil organic matter content over the long term are major gains realized through application of organic resources. Constraints that limit utilization of organic based soil nutrient management systems were also highlighted; with the conclusion that more committed research activity and better adoption of developed technologies would lead to promotion and establishment of the gains of procuring and utilizing organic resources for soil fertility improvement in SSA. Key words: Organic resources, soil fertility, soil organic matter, food security, soil management.

Effect of rhizobia, mycorrhizal fungi and phosphate-solubilizing microorganisms in the rhizosphere of native plants used to recover an iron ore area in Brazil

The iron-ore deposits in Minas Gerais state are concentrated in an area named Ferruginosous Quadrilateral, in which the dominant vegetation belongs to the Cerrado biome (savanna type, called campo rupestre or rupestrian field). This vegetation occurs in altitudes higher than 1000 m and is one of the most endangered biomes of the world. This study aimed to restore an area of rupestrian field used to keep iron-ore products, in which vegetation had been cut and thus resilience did not occur, worsening the low fertility of the fragile soil. Therefore, a revegetation model was proposed using two native species, Centrosema coriaceum (Leguminosae) and Tibouchina multiflora (Melastomataceae), inoculated with selected strains of arbuscular mycorrhizal fungi (AMF) and/or a rhizobium strain. After 48 months of plantation, the plant growth, survival index, physical and chemical soil properties, leaf nitrogen (N) and phosphorous (P), and P soil were evaluated. Inoculated plants benefited in all the analyzed aspects. While T. multiflora presented increased P content in leaves and soil rhizosphere only in inoculated plants, C. coriaceum showed the highest P content in both leaves and soil independently of inoculation. Although the inoculated plants presented more intense root colonization (AMF), the same mycorrhizal species were found in both inoculated and non-inoculated plants of C. coriaceum and T. multiflora. However, species of the Gigasporaceae family were favored in the C. coriaceum rhizosphere, as compared with T. multiflora. In addition, C. coriaceum was able to select in its rhizosphere a rhizobia strain efficient in P solubilization and a large and efficient population of phosphorus solubilizing microorganisms (PSM), preferentially composed of fungi. Through the similarity of their Internal Transcribed Spacer (ITS) sequences, the PSM fungi were identified as Fusarium oxysporum and Aspergillus fischeri using the BLAST database. The data presented suggest that C. coriaceum showed a strong rhizosphere effect in favor of a tripartite action of rhizobia, fungi and AMF populations as strategies to solubilize soil phosphate for survival and plant growth in the rupestrian field. Therefore, the inoculation of these microorganisms is desirable for mine recover.

Laws of sustainable soil management

The challenge of doubling the world’s food grain production by 2030 is even more daunting because of the decrease in per capita arable land area and renewable fresh water resources; increase in risks of soil and environmental degradation; and threat of decrease in use efficiency of inputs because of the projected climate change. Thus, the need for identifying processes, practices and policies that govern sustainable management of soil resources is more critical now than ever before. The goal is to minimize risks of soil degradation by enhancing its resilience and improving ecosystem services of the finite and fragile soil resource. Here, 10 principles are given for sustainable management of soil. This report is an introductory article of the book Sustainable Agriculture, published by Springer, EDP Sciences (Lichtfouse et al. 2009).