Cause Of Soil Degradation Research Articles

Análise de sensibilidade dos parâmetros do modelo SWAT e simulação dos processos hidrossedimentológicos em uma bacia no agreste nordestino

O processo erosivo constitui-se na principal causa de degradação dos solos e é acelerado por intervenções humanas nas bacias hidrográficas, resultando em prejuízos ao setor agrícola e ao meio ambiente. Para a previsão dos impactos de ações antrópicas ou de mudanças climáticas sobre os processos hidrossedimentológicos, os modelos distribuídos e de base física têm sido bastante eficazes. Neste estudo, aplicou-se o modelo SWAT à sub-bacia do Rio Japaratuba Mirim, em Sergipe, nas seções de medição das estações Fazenda Pão de Açúcar (PA) e Fazenda Cajueiro (CJ), com áreas de contribuição respectivamente de 137,3 e 277,8 km², visando à parametrização das duas bacias aninhadas por meio dos processos de calibração e de validação. Foram realizadas simulações do escoamento na bacia menor (PA), a partir dos parâmetros calibrados na bacia maior (CJ), e, reciprocamente, do escoamento na bacia maior (CJ). Em seguida, foram também realizadas simulações do escoamento e da produção de sedimentos para o período de dados de vazão disponíveis (1985 a 2000), para a seção CJ. Os resultados evidenciaram que o modelo calibrado simulou bem o escoamento superficial e conseguiu prever, de forma coerente, a produção de sedimentos com base nos 12 parâmetros mais sensíveis do modelo. A transposição dos parâmetros da bacia maior para a menor e, vice-versa, resultou em índices de Eficiência de Nash-Sutcliffe (NSE) e de Tendência Percentual (PBIAS), considerados satisfatórios para o primeiro caso e insatisfatório para o segundo.

Studying the relationship between water-induced soil erosion and soil organic matter using Vis–NIR spectroscopy and geomorphological analysis: A case study in southern Italy

Soil erosion by water is the main cause of soil degradation in large areas of the Mediterranean belt. Soil erosion determines loss of surface horizon, which is rich in organic matter. The content of soil organic matter (SOM) is a key property for evaluating soil erosion and/or soil preservation and quality. Conventional methods to estimate quantitatively SOM content, based on conventional laboratory analyses, are costly and time consuming. An alternative approach to ascertain SOM content is based on the use of soil spectral reflectance, which has the advantage to be rapid, non-destructive and cost effective. In this study we focused on: (i) using of the laboratory-based, proximally sensed in the visible–near-infrared (Vis–NIR, 400–2500 nm) spectral range to predict SOM content in the study area; (ii) combining soil spectroscopy and geostatistics for mapping SOM content; (iii) mapping zones affected by water erosion processes in the study area; and (iv) analyzing the relationship among soil erosion, SOM and soil spectral data. Areas affected by water erosion processes (sheet wash and/or rill and gully erosions) in the study area were detected through air-photo interpretation and field surveys. Topsoil samples from 215 locations in different soil types and erosion conditions were collected and each sample was air-dried and sieved at 2 mm and then split into two sub-samples: one was used for spectral measurements, while the other was analyzed to determine SOM content. Analysis of spectral curve showed that topsoil samples were spectrally separable on the basis of SOM content and of their erosion severity. Partial least squared regression (PLSR) analysis was applied to establish the relationships between spectral reflectance and SOM content. PLSR was performed on the calibration set including 161 of the 215 available samples, while 54 samples were used as validation set. The optimum number of factors to retain in the calibration model was determined by cross validation. The models were independently validated using the 54 validation soil samples. The results were satisfactory with high adjusted coefficient of determination ( R adj 2 = 0.84) and with a value of residual predictive deviation (RPD) more than 2.4. The results of this work suggest that laboratory reflectance spectroscopy in the Vis–NIR range coupled with a geostatistical analysis can be used as tools for predicting spectrally and mapping SOM. The relationship between water erosion processes and the spatial distribution of SOM, showed that: (i) zones with low content of SOM are affected by water erosion processes and (ii) water erosion affects more than 21% of the study area. • The study aimed at defining soil degradation in a Mediterranean area of south Italy. • Use the Vis–NIR spectroscopy to predict soil organic matter content • Combine soil spectroscopy and geostatistics for mapping soil organic matter content. • Relationship between water erosion, soil organic matter and soil spectral data

Carbon Depletion by Plowing and its Restoration by No‐Till Cropping Systems in Oxisols of Subtropical and Tropical Agro‐Ecoregions in Brazil

AbstractThe continuous use of plowing for grain production has been the principal cause of soil degradation. This project was formulated on the hypothesis that the intensification of cropping systems by increasing biomass‐C input and its biodiversity under no‐till (NT) drives soil restoration of degraded agro‐ecosystem. The present study conducted at subtropical [Ponta Grossa (PG) site] and tropical regions [Lucas do Rio Verde, MT (LRV) site] in Brazil aimed to (i) assess the impact of the continuous plow‐based conventional tillage (CT) on soil organic carbon (SOC) stock vis‐à‐vis native vegetation (NV) as baseline; (ii) compare SOC balance among CT, NT cropping systems, and NV; and (iii) evaluate the redistribution of SOC stock in soil profile in relation to soil resilience. The continuous CT decreased the SOC stock by 0·58 and 0·67 Mg C ha−1 y−1 in the 0‐ to 20‐cm depth at the PG and LRV sites, respectively, and the rate of SOC sequestration was 0·59 for the PG site and ranged from 0·48 to 1·30 Mg C ha−1 y−1 for the LRV site. The fraction of C input by crop residues converted into SOC stock was ~14·2% at the PG site and ~20·5% at the LRV site. The SOC resilience index ranged from 0·29 to 0·79, and it increased with the increase in the C input among the NT systems and the SOC sequestration rates at the LRV site. These data support the hypothesis that NT cropping systems with high C input have a large potential to reverse the process of soil degradation and SOC decline. Copyright © 2013 John Wiley & Sons, Ltd.

Degradation of soils as a result of long-term human-induced transformation of the environment in Iran: an overview

Human-induced soil degradation is a serious and complex environmental challenge in Iran. For a long time, human activities, namely the overuse of land, have been influencing the natural processes on and in soils; therefore, various types of soil degradation can be observed in many parts of the country. The understanding and the consideration of direct and indirect effects of human activities on soils are indispensable for the prediction of the human impact on soil degradation processes. There are many important direct and indirect anthropogenic causes that play an effective role in soil degradation; they have a significant relationship with the natural resource management in Iran. Population dynamics, deforestation, and overgrazing as main causes and salinization, alkalinization, water-logging, soil erosion, and desertification as main effects of human-induced soil degradation are highlighted in this overview. Population in urban areas of Iran strongly increased from 1936 (21% of total population) to 2010 (72% of total population). Nearly 5 million hectares of forest were converted to farmland and urban areas from the 1950s to 2008. The area of Iran's cultivated land was enhanced by more than four times. Livestock population is around three times higher today than the capacity of the rangelands. Regarding this overview the study of land management, soil degradation, and soil conservation in Iran needs an integrative approach. Therefore, a transdisciplinary model to assess environmental, economical and social factors (and thus sustainability), namely in arid and semi-arid areas, is offered too. The most important aim of this overview is the illustration of the principal causes of soil degradation in Iran, highlighting the important subjects for sustainable soil management. The overview also notes that our understanding about human-induced soil degradation in Iran is still at a rudimentary stage; therefore, some research topics need more attention in future.

Subsoiling improves conservation tillage in cereal production of severely degraded Alfisols under Mediterranean climate

Central Chile has a Mediterranean climate with a mean annual precipitation of 695mm, 80% concentrated in winter. In this context, water erosion and inappropriate agricultural management along hillslopes are the major causes of soil degradation. From 2007 to 2010, different agricultural systems were compared: conservation tillage with stubble retained: no tillage (Nt), Nt+subsoiling (Nt+Sb), Nt+barrier hedges (Nt+Bh) and Nt+contour plowing (Nt+Cp). All the systems were compared to conventional tillage (Ct) without crop stubble on the surface. The runoff plots were 50m×20m on a hillside with 12.5% slope in an oat–wheat crop rotation. Runoff, sediment and nutrient losses measured for every rainfall event, occurred during winter months when rainfall energy was also the highest of the whole year. Conservation tillage systems mitigate water erosion compared to the Ct system. In heavy rains, conservation tillage systems reduced soil loss by more than 72% compared to Ct. In addition, the runoff coefficient during the rainy period was 70% lower in conservation tillage systems when the crop was at the initial tillering stage and 90% lower at final tillering. These results show the importance of conservation tillage and crop stubble to decrease erosion, especially in years when extreme precipitation presented a high potential for soil erosion. Moreover, cereal production showed higher biomass and grain yield in Nt+Sb. It was concluded that no tillage with stubble retained on the surface was the best option to mitigate soil erosion. However, the effects of subsoiling decrease over time, making new subsoiling necessary with the implied costs. Due to the strong fluctuations in the prices of the agricultural products, it is impossible to estimate the balance of costs/benefits of this system. On other hand, the duration of the experiment may have been too short to measure the real impacts of no-tillage practices.

Spatial Distribution of Soil Organic Matter Using Geostatistics: A Key Indicator to Assess Soil Degradation Status in Central Italy

Soil organic matter (SOM) content is one of the main factors to be considered in the evaluation of soil health and fertility. As timing, human and monetary resources often limit the amount of available data, geostatistical techniques provide a valid scientific approach to cope with spatial variability, to interpolate existing data and to predict values at unsampled locations for accurate SOM status survey. Using geostatistical and geographic information system (GIS) approaches, the spatial variability of some physical and chemical soil parameters was investigated under Mediterranean climatic condition in the Abruzzo region of central Italy, where soil erosion processes accelerated by human induced factors are the main causes of soil degradation associated with low SOM content. Experimental semivariograms were established to determine the spatial dependence of the soil variables under investigation. The results of 250 soil sampling point data were interpolated by means of ordinary kriging coupled with a GIS to produce contour maps distribution of soil texture, SOM content related to texture, and C/N ratio. The resulting spatial interpolation of the dataset highlighted a low content of SOM in relation with soil texture in most of the surveyed area (87%) and an optimal C/N ratio for only half of the investigated surface area. Spatial location of degraded area and the assessment of its magnitude can provide decision makers with an accurate support to design appropriate soil conservation strategies and then facilitate a regional planning of agri-environmental measures in the framework of the European Common Agricultural Policy.

Impacts of land use changes on soil erosion in Pa Deng sub-district, adjacent area of Kaeng Krachan National Park, Thailand

Soil erosion has been considered as the primary cause of soil degradation since soil erosion leads to the loss of topsoil and soil organic matters which are essential for the growing of plants. Land use, which relates to land cover, is one of the influential factors that affect soil erosion. In this study, impacts of land use changes on soil erosion in Pa Deng sub-district, adjacent area of Kaeng Krachan National Park, Thailand, were investigated by applying remote sensing technique, geographical information system (GIS) and the Universal Soil Loss Equation (USLE). The study results revealed that land use changes in terms of area size and pattern influenced the soil erosion risk in Pa Deng in the 1990–2010 period. The area with smaller land cover obviously showed the high risk of soil erosion than the larger land cover did.

Influence of paddy rice terraces on soil erosion of a small watershed in a hilly area of Northern Vietnam

Soil erosion is the main cause of soil degradation in northern Vietnam. In this study, soil erosion was measured in 2 m2 field plots, a 19.1-ha sub-watershed, and a 248.9-ha main watershed in Tam Quan commune, Tam Duong district, northern Vietnam during 2 years, i.e., 2004–2005. The main watershed includes lowland paddy fields, and is representative for watersheds in the northern Vietnamese landscape. Soil erosion was measured for eight events, at all the three scales to increase our understanding of erosional processes and to assess the effects of paddy fields within the main watershed. The results show that total discharge and sediment yield in both sub-watershed and main watershed were much lower than those in the field plots. Total discharge per unit area in the main watershed was higher than in the sub-watershed, because during the growing season, the paddies are filled with water and any rainfall on them therefore becomes runoff. Sediment yield in the main watershed fluctuated, depending on the soil erosion contribution from many sub-watersheds. Annual rainfalls in 2004 and 2005 were 1,172 and 1,560 mm, respectively, resulting in corresponding total discharges of 54 and 332 mm and total soil losses of 163 and 1,722 kg ha−1 year−1. High runoff volumes occurred in July, August, and September, but April, June, the last 10 days of September and October, were the susceptible periods for soil erosion in the study area because of low plant cover and many agricultural activities during these periods.

Impact of grazing on soil microbial communities along a chronosequence of Acacia tortilis subsp. raddiana in arid soils in Tunisia

Acacia tortilis (Forssk.) subsp. raddiana (Savi) Brenan is a woody legume recommended for adoption in arid lands of Tunisia, but their grazing is recognized as one of the main causes of soil degradation and desertification in these areas. The aim of this research was to explore the effects of grazing intensity on soil properties under A. tortilis subsp. raddiana along a chronosequence of young, mid-aged and old trees. Soil chemical, microbial and biochemical properties were evaluated. The results showed that tree growth increased soil pH, electrical conductivity, soil organic carbon (Corg), microbial biomass carbon (Cmic), Cmic:Corg ratio and enzyme activities (dehydrogenase, phosphatase and β-glucosidase). In contrast, C:N ratio and metabolic quotient (qCO2) decreased with increasing tree age. For the impact of grazing intensity, the amount of organic matter, microbial biomass and enzyme activities were reduced in intensively grazed site, while C:N ratio and metabolic quotient were higher.The findings demonstrated significant impacts of Acacia age-classes and grazing intensity on soil properties. It is concluded that A. tortilis subsp. raddiana establishment and development enhanced the development and the activity of microbial communities in soil; however, intensive grazing was detrimental to soil quality. This indicates that A. tortilis subsp. raddiana improved soil quality and play an important role in soil protection of degraded lands in Tunisia.

Termite and earthworm abundance and taxonomic richness under long-term conservation soil management in Saria, Burkina Faso, West Africa

Unsustainable crop and soil management practices are major causes of soil degradation and declining soil biodiversity in West Africa. Identifying soil management practices that favor macrofauna abundance is highly desirable for long-term soil health. This study investigates the effects of long-term conservation soil management on termite and earthworm abundance and taxonomic richness in the central plateau of Burkina Faso. Trials included rotations with 5 Mg ha −1 yr −2 of organic matter added (established in 1960), application of 10 Mg ha −1 yr −1applied with additional organic (manure or straw) and mineral inputs (established in 1980) and different tillage systems (established in 1990) where 10 Mg ha −1 yr −1 of organic matter was also applied. Soil macrofauna was surveyed at the soil surface and in the upper 30 cm using transect and monolith sampling methods, eight weeks after sorghum crop planting. A total of five termite taxa: Trinervitermes sp., Microtermes sp., Odontotermes magdalenae, Macrotermes sp. and Amitermes stephensoni; belonging to the family of Termitidae, and two earthworm taxa: Dichogaster affinis, Millsonia inermis; from the family of Acanthodrilidae were found. Termite taxonomic richness per treatment ranged between 1 and 4, while earthworm taxa ranged from 0 to 2. Under rotation, one termite taxa and no earthworm taxa were identified. In the organic amendment plots, three termite and two earthworm taxa were found. And light tillage (animal or hand) resulted in four termite taxa and one earthworm taxa. The two types of fauna clearly responded differently to the different conservation soil management practices. Under rotation lower recorded macrofauna population was attributed to the lower rate of applied organic matter compared to levels applied in the organic amendment and tillage trials and where more macrofauna were found. Location of food stock (rooting depth of different crops in the rotation) also had a significant effect on termite presence. Effect of rooting depth on earthworms was not observable due to the absence of earthworms in the rotation trials (possibly due to insecticide application. Manure treatments favored earthworms, while sorghum straw treatments favored termites likely due to respective preference for easy versus difficult to digest organic sources. Animal plowing and hand hoeing had similar and significantly positive effects and both termite and earthworm biological components compared to tractor tillage. We conclude that termite and earthworm abundance and taxonomic richness are most significantly affected by the type and amount of organic matter applied and tillage regimes, with rooting depth of rotations crops also playing a significant role. To promote macrofauna abundance and taxonomic richness in soils, integrated conservation soil management practices with attention to the particular needs and preferences of termites and earthworms is needed.

Persistência do efeito de intervenções mecânicas para a descompactação de solos sob plantio direto

A compactação tornou-se uma das principais causas de degradação do solo em áreas agrícolas, estando diretamente relacionada ao sistema de manejo do solo adotado e, muitas vezes, demandando práticas de descompactação para mitigar esse problema. Este trabalho objetivou avaliar a duração do efeito de intervenções mecânicas, como a aração e escarificação do solo associadas à ação de semeadora de plantio direto equipada com mecanismos rompedores de solo tipo discos e discos + facão, como práticas mitigadoras da compactação de um solo manejado sob o Sistema Plantio Direto (SPD), por meio da avaliação de atributos físicos do solo e do esforço de tração. O estudo foi realizado no município de Coxilha, na região Norte do Rio Grande do Sul, localizado nas coordenadas geográficas de 28°10'18,7" S e 52°22'39,89" O, sobre um Latossolo Vermelho, em experimento instalado no ano de 2001 em área com histórico de oito anos sob SPD. Nessa área foram realizadas intervenções mecânicas anuais, mediante a aração e escarificação do solo, anteriores à implantação da cultura de verão. Os tratamentos de manejo do solo constituíram- se da testemunha, com manutenção ininterrupta do SPD por 16 anos e por seis períodos de tempo de condução desse sistema (7,5; 6,5; 5,5; 4,5; 3,5; e 2,5 anos) após a escarificação ou aração, aplicados nas parcelas principais. Nas subparcelas foram aplicados dois tratamentos de dispositivo de aplicação do adubo no sulco de semeadura (discos duplos defasados e facão + discos). O delineamento experimental adotado foi de blocos completos casualizados com parcelas subdivididas e três repetições. Os resultados indicaram a existência de compactação na camada subsuperficial do solo, situada entre 7 e 15 cm, evidenciada por aumentos na densidade e redução na porosidade total e macroporosidade do solo em todos os tratamentos avaliados. Observou-se que a intervenção mecânica apresenta potencial efêmero para mitigar a compactação e melhorar a estrutura do solo, com duração de até dois anos e meio dos atributos porosidade total e macroporosidade após a escarificação, e a densidade do solo depois da aração. Nos demais atributos avaliados, tais benefícios deixaram de ser perceptíveis em período inferior a dois anos e meio após a intervenção mecânica, o que não provocou alterações na força exercida na barra de tração do trator agrícola, comparativamente à testemunha. Contudo, o mecanismo facão + discos de rompimento do solo na semeadora foi efetivo em alterar os atributos avaliados, aumentando a macroporosidade, diminuindo a microporosidade, a densidade do solo e o esforço de tração e auxiliando, assim, na mitigação da compactação do solo.

Variability of relationships between soil organic carbon and some soil properties in Mediterranean rangelands under different climatic conditions (South of Spain)

Abstract Changes in land use and vegetation cover affect various soil properties, including the soil organic carbon (SOC) pool and the transfer of atmospheric CO2 to terrestrial landscapes. In natural or quasi-natural conditions a reduction in biomass increases the risk of erosion, and can reduce the stored soil organic matter content. This can cause (i) consolidation of low levels of organic carbon stored in the soil; (ii) reduction in the levels of organic carbon because of the onset of erosion processes; and (iii) differing rates of recovery of the soil in response to environmental factors including precipitation, which is a principal agent of indirect recharge of soil organic matter. Few comparable studies have analyzed the reduction of SOC because of erosion, and assessed how this contributes to the loss of soil as vegetation cover decreases. This is particularly the case in semiarid Mediterranean environments, where erosion is one of the main causes of soil degradation. This study presents the results of an experiment carried out along a pluviometric gradient from humid to semiarid Mediterranean conditions, in southern Spain. The study involved two soil depths at five field sites having similar lithology, slope and aspect, but differ in vegetation cover and composition related to their location along the gradient. We used soil cation exchange capacity (CEC) as an indicator of soil degradation. The results showed that: a) SOC decreased with decreasing rainfall; b) SOC is greater at the soil surface than at depth; c) CEC is a good indicator of the degradation of soil surface formations, as it is directly related to the SOC storage capacity; and d) the so-called “Mediterranean mountain” landscape, with sparse and mixed vegetation composed of scrubland and woodland species, is a good organic carbon sink with direct implications in relation to climate change.

English

One of the major causes of soil degradation throughout the world is water erosion. Anionic polyacrylamide (PAM) application to soils is an effective soil conservation practice for reducing runoff and soil losses caused by erosion. It also increases the infiltration rate of soils. The objective of this study was conducted to determine effects of different application rates of PAM (0 (control), 1.667, 3.333 and 5.000 kg.ha-1) on infiltration rate, runoff and soil losses. Polyacrylamide was sprayed on the surface of the experimental soils with different textures. The PAM treated soils were introduced to simulated rainfall at 61 mm/h intensity for an hour. The results indicated that, PAM applications significantly reduced surface runoff and soil losses, but increased infiltration rates. The effectiveness of PAM was higher in clay and clay loam soils than that of sandy clay loam soil. The most effective applications rates of PAM on reducing surface runoff and soil losses and increasing infiltration rates were found to be 3.333 and 5.000 kg.ha-1 . By considering the price and application cost of PAM, It was suggested that 3.333 kg.ha-1 PAM is the most suitable application rate.  As compared with the control, it was obtained that PAM application with a rate of 3.333 kg.ha-1 reduced surface runoff and soil losses by 23.1 and 18.5%, respectively and increased infiltration rate by 24%.     Key words: Polyacrylamide (PAM), soil erosion, soil loss, runoff, infiltration rate, simulated rainfall.

Effect of Converting Secondary Tropical Peat Swamp Forest into Oil Palm Plantation on Selected Peat Soil Physical Properties

Problem statement: The conversion of forest land into oil palm plantation is considered to be one of the causes of soil degradation and loss of tropical land forest in Southeast Asia. The objective of this study was to compare selected peat soil physical properties of secondary tropical peat swamp forest and oil palm plantation to determine the effect of forest conversion. Approach: Peat soil samples were collected from secondary tropical peat swamp forest and oil palm plantation at Batang Igan, Sibu, Sarawak, Malaysia. Experimental plots of 300 m3 were set up in both sites and thirty peat soil samples were collected randomly in both sites at 0-15 cm depth using a peat auger. Undisturbed cores and bulk samples were collected for analysis of bulk density and moisture content. Fiber content of the total mass of organic materials was determined by wet sieving method. Soil bulk density, moisture content, organic matter, mineral content, soil porosity and particle density were determined by standard procedures. Hydraulic conductivity was measured in the field using Model 2800K1 Guelph Permeameter and soil strength was determined using Hand Operated Cone Penetrometer Eijkelkemp. Unpaired T-test was used to compare the variables of the two sites. Results: Both sites had similar degree of decomposition classified as hemic peat. No significant differences in fiber content, moisture content and particle density. Bulk density, mineral content and soil strength were significantly higher in the oil palm plantation while organic matter content, porosity and saturated hydraulic conductivity were significantly higher in the secondary tropical peat swamp forest. Conclusion: Conversion of secondary tropical peat swamp forest to oil palm plantation has significantly increased soil bulk density, mineral content and soil strength but significantly decreased organic matter content, porosity and saturated hydraulic conductivity. However, degree of decomposition, fiber content, moisture content and particle density were not affected by the conversion.

Small ruminant impacts on rangelands of semiarid highlands of Mexico and the reconverting by grazing systems

The north-central semiarid region of Mexico has been exposed to systematic grazing since colonial times. The grazing impact on rangelands has degraded soils and reduced diversity and productivity. The most common and detrimental cause of soil degradation is soil erosion which destroys chemical, physical and biological properties. To determine the effect of grazing systems on rangelands, several studies were performed. Such studies included a description of soil profiles to categorize degradation and the evaluation of water erosion changes due to further degradation processes under grazing systems (rotational, RG and continuous, CG). The study was carried out on a rangeland of the ejido Pánuco, Zacatecas, from 2002 to 2005. Soil degradation was classified by identifying 6 groups with similar soil profiles (GSSP) which were described as: (1) low degradation soil; (2) medium degradation soil with A horizon lost; (3) high degradation soil without A and B horizons lost; (4) high degradation soil with in situ development; (5) high degradation soil with calcareous material; and (6) high degradation soil without development, which is a very shallow soil above the parental material. Further degradation was determined by soil erosion measurements performed in the study area and the surroundings. With respect to soil losses their values were systematically less for the RG system under the native vegetation conditions studied ( P < 0.01). Changes in the production systems may imply a reconversion of the system. Some changes include a modification in the intensity of use of rangelands, starting with a new grazing system, as well as changes in technology which may be simulated by GIS.

Wind erosion on mining waste in southeast Spain

AbstractMining activities are one of the most persistent causes of soil degradation by pollution of heavy metals on the planet. They generate huge amounts of wastes that are deposited over extensive areas. Due to the grain size of the mining wastes, they are prone to wind erosion. As a consequence of their composition with heavy metal, the eroded material can be a potential pollutant of soil and air. This means they are potential pollutants of both the atmosphere and the surrounding soils, not to mention the high risk on they pose the nearby populations.This research evaluates the amount of wind‐mobilized material and its heavy metal content in sterile slag ponds located in the Cartagena–La Unión area (southeast Spain), which had been a mining area for thousands of years until its demise in 1991. Specific collectors were designed to measure the sediment transported by the wind into the dust traps. They were placed on sterile lag at three heights (21, 42 and 63 cm.) and eight wind directions (N, NE, E, SE, S, SW, W, NW).The results show a high concentration of heavy metals, especially zinc and lead, which could have harmful effects on nearby towns, farming areas and beaches. In some cases, soils located near mining areas, which could potentially be turned over to agriculture, are degraded by heavy metal pollution to the extent that practically they can be considered as desert. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Changes in soil properties following conversion of Acacia senegal plantation to other land management systems in North Kordofan State, Sudan

Changes in soil texture, bulk density, pH, concentrations and stocks of OC, N, P and K before and after conversion of a 6-year-old Acacia senegal plantation to other land management systems (LMS) were investigated, after three cropping seasons, in the drylands of western Sudan. LMS included pure and intercropped sorghum (PS), roselle (PR) and grasses (PG) with A. senegal at high- and low-tree densities (HD 433 and LD 266 trees ha −1). Significant changes included increase in coarse sand and a decrease in fine sand under pure and intercropped systems at LD; decrease in clay contents in PS and PR; an increase in clay ratio in all pure crops and HD + R; a decrease in aggregated mean concentrations of OC, N and P under all LMS by 42%, 68% and 45%, respectively; increase in soil pH under all LMS; a depletion of aggregated mean stocks of OC, N, P and K in all LMS by 38%, 30%, 52% 13%, respectively. The study established that wholesale tree clearance constitutes a major cause of soil degradation, and tree inputs and cycling of nutrients are of major importance to soil fertility in the study area.

Changes in shrinkage of restored soil caused by compaction beneath heavy agricultural machinery

SummaryCompaction is a major cause of soil degradation. It affects not only the porosity of the soil, but also the soil’s hydrostructural stability. Soil that is restored after temporary removal is particularly sensitive to compaction. We investigated the effects of trafficking with a heavy combine harvester on the shrinkage behaviour of a restored soil that had been gently cultivated for several years. We tested the hypothesis that compaction decreases the hydrostructural stability of restored soil by analysing simultaneously measured shrinkage and water retention curves of undisturbed soil samples. Shrinkage strongly depended on clay and organic carbon content. Taking account of this influence and normalizing the shrinkage parameters with respect to these soil properties, we found pronounced effects of trafficking on shrinkage. Ten passes with the combine harvester decreased the structural porosity by about 40% at maximum swelling and by about 30% at the shrinkage limit and increased the bulk density by 8% at maximum swelling and by 10% at the shrinkage limit, but did not significantly affect the porosity of the soil plasma. Moreover, trafficking modified shrinkage, increasing the slopes of the shrinkage curve in the basic and structural shrinkage domains by about 30% and more than 150% after 10 passes, respectively. Evidently the aggregate structure was strongly destabilized. The results indicate that the hydrostructural stability of the soil was still very sensitive to compaction by trafficking even 5 years after restoration. The analysis of shrinkage seemed well suited for the assessment of compaction effects on soil structure.

Dégradation des sols et stratégies coopératives en Méditerranée : la pression sur les ressources naturelles et les stratégies d

Soil erosion and salinisation emerged very early in the Mediterranean region along with the introduction of agriculture and irrigation. Nowadays, in all Mediterranean countries, other forms of soil degradation are obvious: they are still poorly documented and their severity and risks have not been assessed. Agriculture is no longer the only cause of soil degradation: urbanism, industry, transportation, handicraft and leisure also contribute. The state of the art inventory suggests that soil degradation is very swift in the Mediterranean region and that in some situations the thresholds of irreversibility have already been reached or even exceeded. The complexity of the phenomena, with their inter-relations and overlapping and their sometimes trans-border impacts, call for research efforts exceeding the framework and means of the separate States. A Mediterranean policy in favour of soils is therefore necessary.

Tillage-induced CO 2 loss across an eroded landscape

Soil carbon (C) losses and soil translocation from tillage operations have been identified as causes of soil degradation and soil erosion. The objective of this work was to quantify the variability in tillage-induced carbon dioxide (CO 2) loss by moldboard (MP) and chisel (CP) plowing across an eroded landscape and relate the C loss to soil properties. The study site was a 4 ha wheat ( Triticum aestivum L. cv. Marshall) field with rolling topography and five soil types in the Svea-Barnes complex in west central Minnesota (N. Latitude = 45°41′W, Longitude = 95°43′). Soil properties were measured at several depths at a 10 m spacing along north–south (N–S) and west–east (W–E) transects through severely eroded, moderately eroded and non-eroded sites. Conventional MP (25 cm deep) and CP (15 cm deep) equipment were used along the pre-marked transects. Gas exchange measurements were obtained with a large, portable chamber within 2 m of each sample site following tillage. The measured CO 2 fluxes were largest with the MP > CP > not tilled (before tillage). The variation in 24 h cumulative CO 2 flux from MP was nearly 3-fold on the N–S transect and 4-fold on the W–E transect. The surface soil organic C on the transects was lowest on the eroded knolls at 5.1 g C kg −1 and increased to 19.6 g C kg −1 in the depositional areas. The lowest CO 2 fluxes were measured from severely eroded sites which indicated that the variation in CO 2 loss was partially reflected by the degradation of soil properties caused by historic tillage-induced soil translocation with some wind and water erosion. The spatial variation across the rolling landscape complicates the determination of non-point sources of soil C loss and suggests the need for improved conservation tillage methods to maintain soil and air quality in agricultural production systems.