Chemistry, availability and mobility of molybdenum in Colorado soils, The

December 1975.Covers not scanned.Includes bibliographical references.Print version deaccessioned 2022.The purpose of this study was to investigate the impact of molybdenum contamination in irrigation water on soils and pastures in Colorado. The chemistry, availability and mobility of Mo was studied in the laboratory, greenhouse, and field. These results were incorporated into a dynamic computer simulation model that predicts Mo accumulation in forages. Solubility diagrams were constructed from thermodynamic data for naturally occurring molybdenum minerals. The solubility of molybdenum in selected Colorado soils was compared with that predicted by the solubility diagrams. Molybdenum minerals were found to control the solubility of Mo in only one of the thirteen soils studied. Addition of wulfenite (PbMoO4), the most stable Mo mineral, raised the Mo solubility to conform to the solubility isotherm of wulfenite in soils. In the remaining twelve soils the solubility of Mo was controlled by specific adsorption processes, and changed with the degree of Mo saturation and pH. The Freundlich adsorption isotherm was extended with a pH term to describe the solubility relationship of Mo in soils. The availability of Mo in soils was studied in both greenhouse and field. Additions of Na2MoO4 to soils increased the uptake of Mo by alfalfa, clover, and bluegrass; the uptake increased with alkalinity. Water-extractable or (NH4)2CO3-extractable soil Mo accurately predicted the concentration of Mo in alfalfa grown on neutral and alkaline soils (r= .97 in the greenhouse, and r= .85 in the field). The information obtained in the laboratory and greenhouse studies was used to develop a computer model to simulate the impact of high-Mo irrigation water on soils and forages. The model used simulated daily growth of alfalfa under climatic conditions typical for Colorado. Changes in the Mo content of the rhizosphere were evaluated daily by considering inputs from irrigation water and losses from leaching and plant uptake. The impact of Mo contamination on forage was shown to depend on the quality and amount of irrigation water applied to the field, as well as on the type and leachability of the soil. Toxic levels of Mo were predicted for alfalfa grown on a clayey soil after 15 years of irrigation with 300 mm of water containing 100 ppb Mo. It was demonstrated that most soils irrigated with water containing more than 25 ppb Mo will eventually produce toxic forages

Desertification : Concept, causes and amelioration

Desertification is a condition of human-induced land degradation that occurs in arid, semiarid and dry sub-humid regions (precipitation/potential evapotranspiration or P/ETP 0.05 to 0.65) and leads to a persistent decline in economic productivity (> 15% of the potential) of useful biota related to a land use or a production system. Climatic variations intensify the decline in productivity, restorative management mitigates it. Drylands or territories susceptible to desertification occupy 39.7% (~ 5.2 billion ha) of the global terrestrial area (~ 13 billion ha). The highest concentration of drylands occurs in Africa, Asia and Australia. Two out of every three hectares of drylands suffer from land degradation of one kind or another. Barring 78 M ha which are irreversibly degraded, the remainder area - affected by desertification - is reclaimable at a price. Desertification is caused primarily by over-exploitation of natural resources beyond their carrying capacity. Solutions to combat desertification lie in the management of the causes of desertification. However, there are no easy options to combat it. While managing demographic pressure should receive priority, the solutions to combat desertification involve local action, guided by land use and climatic conditions and in harmony with local needs and people’s expectations. Drylands are used as rangelands or as croplands, with the latter either irrigated or rainfed. Integrated data on land and soil degradation and on the socio-economic environment within which it occurs are the basis to formulate strategies for reclamation and proper use of drylands. Rangelands constitute the dominant land use (est. 88%) in the territories susceptible to desertification. Of the 3333 M ha rangeland area affected by land degradation 757 M ha are severely affected., 72 M ha irreversibly. Within rangelands, vegetation degradation is the primary cause of desertification – it represents 72% of the total area desertified worldwide (2576 M ha out of 3592 M ha). Overgrazing by excessive numbers of low productivity livestock and fuel wood extraction by man are the principal causes of vegetation degradation. Centralized management of common rangeland resources and insecure tenancy laws stand in the way of communities and herders adopting a long-term view to conserve and invest in range improvement measures. Inadequate dissemination of knowledge on vegetation improvement methods is another cause of rangeland degradation. Five suggestions are made to assure sustainability and effectiveness of rangeland management programs: (1) shifting to community management of rangelands that have been nationalized, (2) granting formal rights to individual transhumance herders that have been settled, (3) providing education and training on range management and improvement, (4) introducing elite breeds of livestock for high productivity, and (5) implementing programs for harnessing alternative sources of energy for cooking (solar and biogas). Rainfed croplands occupy an area of 457 M ha, 216 M ha of which have degraded soils. Some 4 M ha suffer from irreversible degradation. Of the remainder, 29 M ha and 183 M ha are, respectively, affected by severe (reclaimable with engineering works) and moderate degradation. Soil constraints in rainfed croplands arise primarily from their vulnerability to erosion, which leads to loss of organic matter, fertility and rooting depth. Eroded soils are structurally unstable and are prone to crusting and compaction. Risk arising from drought susceptibility and poverty limit the adoption of restorative management. Rainwater conservation to minimize risk is not adopted due to insecure tenancy and centralized management of government supported programs. A lack of adequate knowledge and skills of efficient use and storage of rainwater allow degradation processes to proceed unchecked. The imperatives to succeed are: (1) land tenure policies towards freehold ownership; (2) community participation in the management of rainwater, (3) efficient use of harvested water supported by high value land use options built on indigenous knowledge and (4) government support to facilitate the development of rainfed agriculture. Irrigated croplands occupy an area of 145 M ha. Of this, 2 M ha are affected by irreversible degradation and 41 M ha suffer from reversible degradation, mainly from salinity and waterlogging. The mechanisms of salinity development differ and so do the solutions when canal or underground water is used for irrigation. With canal water irrigation, three key development options are suggested to remove excess salts and water and to minimize conveyance and application losses of water: (1) effective drainage, (2) properly lined or closed water conveyance systems and efficient irrigation techniques, and (3) participatory management of irrigation systems. The costs of installing drainage and leak-proof conveyance systems are high, but so are the economic and ecological gains. With underground water use, salinity develops as the water reserves are depleted due to over-extraction. While efficient methods of irrigation can help in postponing the occurrence of salinity, sustainable solutions lie in balancing the water withdrawals with recharge. Efforts should therefore be made to promote groundwater replenishment through runoff harvesting. Although it is not always possible to recharge the deep aquifers with the limited quantities of runoff produced by the low annual precipitation, still, the use of harvested runoff for irrigation can save groundwater. Once water-efficient systems are operational, cropping systems that maximize productivity per unit of water can be introduced. The entire strategy of reclaiming desertified land revolves around water, the reestablishment of the vegetation of rangelands, the rejuvenation of the productivity of rainfed croplands, and the halting of loss of irrigated farmlands. Humans play a central role in that strategy; desertification begins and ends with human action. Unless it ends, the estimated 900 million people affected today will grow to billions tomorrow

Global inventory of Wetlands and their role in the carbon cycle

Wetlands are among the most important natural resources on earth, as sources of biological, cultural and economic diversity. Conservation and management of wetlands have been identified as priority tasks for action in international conventions and regional policies, but extensive wetland area has been degraded in many developing countries. These continuing destruction demands to be restricted or at least slowed down. The primary objectives of this study were (i) assessing ecological functions and concepts for sustainable use of wetlands and (ii) compiling relevant information sources on geographic distribution of wetlands as well as their role in the global carbon budget. Wetlands comprise a pivotal global carbon reservoir and can moreover sequester additional carbon from the atmosphere in form of soil organic matter. Pristine wetland soils are a source of the greenhouse gas methane, but- under improper management - these soils emit even larger quantities of the greenhouse gas carbon dioxide. The discussion on wetland protection measures is thwarted by uncertainties in the estimated carbon pool sizes and flux rates. On the global scale, the estimates on the carbon pool size vary from 200 to 530 Gt C while our own assessment (by incorporating global soil maps) clearly points towards the lower end of this range. Likewise, estimates of the carbon sequestration potential of wetlands vary between 80 to 230 Tg C/ yr. These discrepancies may in part be due to inherent problems in global land cover surveys, but diverging definitions of the ecosystem 'wetlands' (especially in dealing with peatlands) are further confounding an appraisal of global wetland resources. Similar uncertainties as for the global estimates arise for the geographic distribution of wetlands as described in different data sources. The three published world maps on wetland resources only coincide in 20-30 % of the identified wetland area. Our compilation of data on quantity and distribution of the wetland carbon pool allows an identification of potential hot spots' of future emissions and could feed into development of research and conservation projects. There are many reasons in favor of protection or a 'wise use' of wetlands that maintains the basic features of the ecosystem. The significance of wetlands for the global carbon budget and thus, for climate change, is a crucial pro-conservation argument that has been substantiated in this study through findings from current research

Global inventory of wetlands and their role in the carbon cycle

Wetlands are among the most important natural resources on earth, as sources of biological, cultural and economic diversity. Conservation and management of wetlands have been identified as priority tasks for action in international conventions and regional policies, but extensive wetland area has been degraded in many developing countries. These continuing destruction demands to be restricted or at least slowed down. The primary objectives of this study were (i) assessing ecological functions and concepts for sustainable use of wetlands and (ii) compiling relevant information sources on geographic distribution of wetlands as well as their role in the global carbon budget. Wetlands comprise a pivotal global carbon reservoir and can moreover sequester additional carbon from the atmosphere in form of soil organic matter. Pristine wetland soils are a source of the greenhouse gas methane, but – under improper management – these soils emit even larger quantities of the greenhouse gas carbon dioxide. The discussion on wetland protection measures is thwarted by uncertainties in the estimated carbon pool sizes and flux rates. On the global scale, the estimates on the carbon pool size vary from 200 to 530 Gt C while our own assessment (by incorporating global soil maps) clearly points towards the lower end of this range. Likewise, estimates of the carbon sequestration potential of wetlands vary between 80 to 230 Tg C/ yr. These discrepancies may in part be due to inherent problems in global land cover surveys, but diverging definitions of the ecosystem 'wetlands' (especially in dealing with peatlands) are further confounding an appraisal of global wetland resources. Similar uncertainties as for the global estimates arise for the geographic distribution of wetlands as described in different data sources. The three published world maps on wetland resources only coincide in 20-30 % of the identified wetland area. Our compilation of data on quantity and distribution of the wetland carbon pool allows an identification of potential ‘hot spots' of future emissions and could feed into development of research and conservation projects. There are many reasons in favor of protection or a 'wise use' of wetlands that maintains the basic features of the ecosystem. The significance of wetlands for the global carbon budget and thus, for climate change, is a crucial pro-conservation argument that has been substantiated in this study through findings from current research

Peak phosphorus: Implications for agricultural production, the environment and development

Phosphorus is a key element in food production, but is a non-renewable resource. Recent estimates suggest that global production of P fertilizers will peak in 2033 and will be one third of that peak level by the end of the 21st century. Population and income growth will increase demand for food, and especially animal protein, the production of which will accelerate the rundown in P reserves and the consequential rise in fertilizer prices. The global distribution of current P fertilizer use divides countries into the haves which in many cases face severe pollution problems from excess P, and the have-nots in which low input use annually drains soil P reserves. Coping strategies include improvements in the efficiency of fertilizer P manufacture and use, and the recycling of P in liquid and solid wastes. The latter approach offers win-win solutions by reducing the environmental pollution of water in highly populated areas. Future utilisation of scarce P reserves requires policy decisions that take account of equity, productivity, environmental and trade considerations. Biological solutions designed to increase P use efficiency, such as improving crop varieties and mycorrhiza associations, and the use of P accumulating plants as green manures, are also considered

Peak phosphorus : Implications for agricultural production, the environment and development

Phosphorus is a key element in food production, but is a non-renewable resource. Recent estimates suggest that global production of P fertilizers will peak in 2033 and will be one third of that peak level by the end of the 21st century. Population and income growth will increase demand for food, and especially animal protein, the production of which will accelerate the rundown in P reserves and the consequential rise in fertilizer prices. The global distribution of current P fertilizer use divides countries into the ‘haves’ which in many cases face severe pollution problems from excess P, and the ‘have-nots’ in which low input use annually drains soil P reserves. Coping strategies include improvements in the efficiency of fertilizer P manufacture and use, and the recycling of P in liquid and solid wastes. The latter approach offers win-win solutions by reducing the environmental pollution of water in highly populated areas. Future utilisation of scarce P reserves requires policy decisions that take account of equity, productivity, environmental and trade considerations. Biological solutions designed to increase P use efficiency, such as improving crop varieties and mycorrhiza associations, and the use of P accumulating plants as green manures, are also considered

Nutrient flows in agricultural production and international trade: Ecological and policy issues

This paper addresses the issue of environmental and ecological impacts of nutrient flows within and between countries by reviewing and presenting data on nutrient balances and global nutrient movements. The results for nutrient depletion in agricultural soils during 1996-1999 show that in most countries in Africa and Latin America and the Caribbean rates of depletion are so high that current land use is not sustainable. At the other end of the scale, nutrient surplus derived from agriculture is most serious in the USA and industrialized countries of Europe, but also occurs in some densely populated areas of countries such as India and China. International net flows of NPK in traded agricultural commodities were estimated to total 4.8 Tg in 1997 and predicted to increase to 8.8 Tg in 2020. Flows vary widely across regions. Major net importers of NPK are West Asia/North Africa and China. Although soils in countries of Sub-Saharan Africa are widely known to be heavily degraded due to nutrient depletion, this region is nevertheless a net importer of NPK in agricultural commodities. However, the nutrients imported in food and feed commodities to Sub-Saharan countries are commonly concentrated in the cities creating waste disposal problems rather than alleviating deficiencies in rural soils. Countries with a net loss of NPK in agricultural commodities are the major food exporting countries the United States, Australia, and some countries of Latin America. A wide range of policy measures influence agricultural trade, nutrient flows and balances. The effects of agricultural trade liberalization and the reduction of production subsidies are briefly described, as well as more direct environmental policies like nutrient accounting schemes, eco-labeling, and nutrient trading. Our study highlights the need for environmental costs to be factored into the debate on nutrient management and advocates more interdisciplinary research on these important problems

Nutrient flows in agricultural production and international trade : Ecology and policy issues

This paper addresses the issue of environmental and ecological impacts of nutrient flows within and between countries by reviewing and presenting data on nutrient balances and global nutrient movements. The results for nutrient depletion in agricultural soils during 1996-1999 show that in most countries in Africa and Latin America and the Caribbean rates of depletion are so high that current land use is not sustainable. At the other end of the scale, nutrient surplus derived from agriculture is most serious in the USA and industrialized countries of Europe, but also occurs in some densely populated areas of countries such as India and China. International net flows of NPK in traded agricultural commodities were estimated to total 4.8 Tg in 1997 and predicted to increase to 8.8 Tg in 2020. Flows vary widely across regions. Major net importers of NPK are West Asia/North Africa and China. Although soils in countries of Sub-Saharan Africa are widely known to be heavily degraded due to nutrient depletion, this region is nevertheless a net importer of NPK in agricultural commodities. However, the nutrients imported in food and feed commodities to Sub-Saharan countries are commonly concentrated in the cities creating waste disposal problems rather than alleviating deficiencies in rural soils. Countries with a net loss of NPK in agricultural commodities are the major food exporting countries – the United States, Australia, and some countries of Latin America. A wide range of policy measures influence agricultural trade, nutrient flows and balances. The effects of agricultural trade liberalization and the reduction of production subsidies are briefly described, as well as more direct environmental policies like nutrient accounting schemes, eco-labeling, and nutrient trading. Our study highlights the need for environmental costs to be factored into the debate on nutrient management and advocates more inter- disciplinary research on these important problems

Trade-offs in multi-purpose land use under land degradation

CITATION: Vlek, P. L. G., et al. 2017. Trade-offs in multi-purpose land use under land degradation. Sustainability, 9(12):2196, doi:10.3390/su9122196.The original publication is available at http://www.mdpi.com/journal/sustainabilityAbstract: Land provides a host of ecosystem services, of which the provisioning services are often considered paramount. As the demand for agricultural products multiplies, other ecosystem services are being degraded or lost entirely. Finding a sustainable trade-off between food production and one or more of other ecosystem services, given the variety of stakeholders, is a matter of optimizing land use in a dynamic and complex socio-ecological system. Land degradation reduces our options to meet both food demands and environmental needs. In order to illustrate this trade-off dilemma, four representative services, carbon sinks, water storage, biodiversity, and space for urbanization, are discussed here based on a review of contemporary literature that cuts across the domain of ecosystem services that are provided by land. Agricultural research will have to expand its focus from the field to the landscape level and in the process examine the cost of production that internalizes environmental costs. In some situations, the public cost of agriculture in marginal environments outweighs the private gains, even with the best technologies in place. Land use and city planners will increasingly have to address the cost of occupying productive agricultural land or the conversion of natural habitats. Landscape designs and urban planning should aim for the preservation of agricultural land and the integrated management of land resources by closing water and nutrient cycles, and by restoring biodiversity.https://www.mdpi.com/2071-1050/9/12/2196Publisher's versio