Showing papers in "Advances in Agronomy in 2008"

Some Prospective Strategies for Improving Crop Salt Tolerance

Abstract: Soil salinity is a major environmental constraint to crop productivity worldwide. The “biological” approach to this problem focuses on the management, exploitation, or development of plants able to thrive on salt‐affected soils. This chapter reviews strategies by which plants can be enabled to grow on saline soils. The first strategy is to prime seeds before planting by treating them with inorganic or organic chemicals and/or with high or low temperatures. The second strategy involves exogenous application of organic chemicals, such as glycine betaine, proline, or plant growth regulators, or inorganic chemicals to plants under salinity stress. Considerable improvements in growth and yield have been reported in a number of crops using these approaches. The third strategy is to employ selection and breeding. Major efforts have been made to develop salt‐tolerant lines or cultivars of crops using conventional plant breeding. However, the complexity of the tolerance mechanisms, lack of selection criteria, and variation in responses of plants at different developmental stages have resulted in only limited success. The emphases for developing salt‐tolerant lines/cultivars are now on marker‐assisted breeding and genetic transformation. The development of salt‐tolerant transgenic plants is still at an early stage but may become increasingly more effective as better knowledge of the complex mechanisms involved in plant salt tolerance is acquired. Furthermore, the rapid expansion in knowledge on genomics and proteomics will undoubtedly accelerate the transgenic and molecular breeding approaches However, to date, there are few conclusive reports indicating successful performance of transgenic cultivars under natural stressful environments.

Will Stem Rust Destroy the World’s Wheat Crop

Abstract: Race Ug99, or TTKSK, of fungus Puccinia graminis tritici, causing stem or black rust disease on wheat (Triticum aestivum), first identified in Uganda in 1998 has been recognized as a major threat to wheat production. Its spread in 2006 to Yemen and Sudan and further spread towards North Africa, Middle East and West-South Asia is predicted -aided by predominant wind currents and large areas of wheat varieties that are susceptible and grown under environments favorable for survival and multiplication of the pathogen. This has raised serious concerns of major epidemics that could destroy the wheat crop in these primary risk areas. Detection in Kenya of a new variant TTKST in 2006 with virulence to gene Sr24, which caused severe epidemics in 2007 in some regions of Kenya and rendered about half of the previously known Ug99-resistant global wheat materials susceptible, has further increased the vulnerability globally. Rigorous screening since 2005 in Kenya and Ethiopia of wheat materials from 22 countries and International Centers has identified low frequency of resistant materials that have potential to replace susceptible cultivars. Diverse sources of resistance, both race-specific and adult-plant type, are now available in high-yielding wheat backgrounds and are being used in breeding. The proposed strategy is to deploy spring wheat varieties possessing durable, adult plant resistance in East Africa and other primary risk areas to reduce inoculum and selection of new virulences capable of overcoming undefeated race-specific resistance genes. Race-specific resistance genes can then be deployed in secondary risk areas preferably in combinations. We believe that Ug99 threat in most countries can be reduced to low levels by urgently identifying, releasing and providing seed of new high yielding, resistant varieties.

Chapter 7 Ameliorating Soil Acidity of Tropical Oxisols by Liming For Sustainable Crop Production

Abstract: The greatest potential for expanding the world's agricultural frontier lies in the savanna regions of the tropics, which are dominated by Oxisols. Soil acidity and low native fertility, however, are major constraints for crop production on tropical Oxisols. Soil acidification is an ongoing natural process which can be enhanced by human activities or can be controlled by appropriate soil management practices. Acidity produces complex interactions of plant growth‐limiting factors involving physical, chemical, and biological properties of soil. Soil erosion and low water‐holding capacity are major physical constraints for growing crops on tropical Oxisols. Calcium, magnesium, and phosphorous deficiencies or unavailabilities and aluminum toxicity are considered major chemical constraints that limit plant growth on Oxisols. Among biological properties, activities of beneficial microorganisms are adversely affected by soil acidity, which has profound effects on the decomposition of organic matter, nutrient mineralization, and immobilization, uptake, and utilization by plants, and consequently on crop yields. Liming is a dominant and effective practice to overcome these constraints and improve crop production on acid soils. Lime is called the foundation of crop production or “workhorse” in acid soils. Lime requirement for crops grown on acid soils is determined by the quality of liming material, status of soil fertility, crop species and cultivar within species, crop management practices, and economic considerations. Soil pH, base saturation, and aluminum saturation are important acidity indices which are used as a basis for determination of liming rates for reducing plant constraints on acid soils. In addition, crop responses to lime rate are vital tools for making liming recommendations for crops grown on acid soils. The objective of this chapter is to provide a comprehensive and updated review of lime requirements for improved annual crop production on Oxisols. Experimental data are provided, especially for Brazilian Oxisols, to make this review as practical as possible for improving crop production.

Combining biomarker with stable isotope analyses for assessing the transformation and turnover of soil organic matter

Abstract: Soil organic matter (SOM) consists of a vast range of biomolecules, but their individual contribution to the biogeochemical cycling of nutrients and CO2 release has eluded researchers. Here, we review the current knowledge on combining biomarker with stable isotope analyses for identifying the mechanisms and rates of SOM genesis and transformation. After an overview of the major biomarkers that are used for identifying decomposer communities and the origin of SOM far beyond microbial life cycles, we reexplain the principles and potentials of applying artificial and natural stable isotope labeling techniques in soil research. Major focus is finally laid on the quantitative evaluation of the published compound-specific stable isotope data of soils to characterize the niches and activity of soil microorganisms as well as their role in controlling the short-to long-term fate of SOM. Our literature research suggested that fungi appear to feed mainly on fresh plant material, whereas gram-positive bacteria also consume both fresh and older SOM. The newly synthesized structures have apparent mean residence time (MRT) of 1–80 years, while refractory plant-derived biomarkers may even dissipate faster. In no case did we find evidences for inert soil C. However, MRT was not constant but increased with increasing time after C3/C4 vegetation change. It is concluded that calculated MRTs from C3/C4 vegetation changes are currently underestimated, because,there is also a the formation of stable C4-derived C pools that did not reach steady-state equilibrium within few decades.

Impact of Global Warming on Soil Organic Carbon

Abstract: Soils contain a stock of carbon that is about twice as large as that in the atmosphere and about three times that in vegetation. Small losses from this large pool could have significant impacts on future atmospheric carbon dioxide concentrations, so the response of soils to global warming is of critical importance when assessing climate carbon cycle feedbacks. Models that have coupled climate and carbon cycles show a large divergence in the size of the predicted biospheric feedback to the atmosphere. Central questions that still remain when attempting to reduce this uncertainty in the response of soils to global warming are (1) the temperature sensitivity of soil organic matter, especially the more recalcitrant pools; (2) the balance between increased carbon inputs to the soil from increased production and increased losses due to increased rates of decomposition; and (3) interactions between global warming and other aspects of global change, including other climatic effects (e.g., changes in water balance), changes in atmospheric composition (e.g., increasing atmospheric carbon dioxide concentration) and land‐use change. In this chapter, we review trends in warming, factors affecting the response of soil carbon to global warming, evidence on the balance between changes in production and soil organic matter decomposition, recent research on the temperature sensitivity of soil organic carbon pools, methods for measuring soil responses to global warming, approaches to modeling soil responses to global warming, regions/ecosystems likely to be most vulnerable to future warming, and available technologies to reduce vulnerability of soil carbon to the impacts of future global warming.

Chapter 3 Crop Residue Management for Lowland Rice-Based Cropping Systems in Asia

Abstract: Intensification of rice-based cropping systems in Asia has substantially increased production of food and associated crop residues. The interval between crops in these systems is often brief, making it attractive for farmers to burn residues in the field to hasten and facilitate tillage for the next crop. Open-air burning causes serious air quality problems affecting human health and safety, and it has been banned by many Asian governments. In this chapter, we evaluate for rice-based cropping systems existing and emerging in-field alternatives to burning residues based on criteria of productivity, profitability, environmental impact, and sustainability. In intensive rice monocropping systems, residue is typically managed under conditions of soil flooding and anaerobic decomposition during the rice crop. In systems, where rice is rotated with an upland (non-flooded) crop, there are two major categories: residue of upland crop managed during flooded rice and rice residue managed during the upland crop. One option during the flooded rice crop is incorporation of residues from the previous rice or upland crop into the soil. Many studies have examined incorporation of crop residue during land preparation for flooded rice. In the vast majority of cases there was no significant increase in yield or profit. Residue decomposition in anaerobic flooded soil substantially increases methane (CH 4 ) emission relative to residue removal. Surface retention of residue during rice cropping is challenging to implement because residue must be removed from the field during conventional tillage with soil flooding (i.e., puddling) and then returned. Alternatively, rice must be established without the traditional puddling that has helped sustain its productivity. Mulch is a good option for rice residue management during the upland crop, especially with reduced and no tillage. Mulch can increase yield, water use efficiency, and profitability, while decreasing weed pressure. It can slightly increase nitrous oxide (N 2 O) emission compared with residue incorporation or removal, but N fertilization and water management are typically more important factors controlling N 2 O emission than residue management. Long-term studies of residue removal have indicated that removing residue from continuous rice systems with near continuous soil flooding does not adversely affect soil organic matter (SOM). The use of crop residue as a mulch with reduced or no tillage for upland crops should be promoted in rice-based cropping systems. On the contrary, residues from the crop preceding rice on puddled and flooded soil can be considered for removal for off-field uses.

Microbial distribution in soils: physics and scaling

Abstract: In a handful of fertile soil there are billions of microorganisms and yet, even with a conservative estimate, the surface area covered by these organisms is considerably less than 1%. What does this tell us about the function of the physical structure in which soil organisms reside and function, collecting, and separating micropopulations from each other and from resources? It would seem that most of the soil is akin to desert regions with little life been supported on its terrains, yet with vast communities of individuals, from an amazing array of species, supported in small-scale habitats, connected or disconnected by saturated or unsaturated pore space over relatively short time-scales. The biodiversity of these communities remains impressive yet overall functionally illusive, bar some considerations of inbuilt redundancy. What is far more impressive is the range of habitats on offer to populations with short-term evolutionary time frames. The availability of spatially and temporally diverse habitats probably gives rise to the biodiversity that we see in soil. It is not too far fetched to state that the majority of habitats on Earth (and indeed extraterrestrial) are revealed in that handful of soil. The key question is what is the functional consequence of such habitat heterogeneity? To answer this it is clear that we need to bring together a new discipline that combines the biology and physics of the soil ecosystem. This biophysical approach, combined, where required, with important mineral-microbe knowledge is needed to help us understand the mechanisms by which soils remain productive, and to identify the tipping-points at which there may be no return to sustainability. This review aims to highlight the importance of addressing the soil ecosystem as a dynamic heterogeneous system focusing on microbiota–habitat interactions.

Imaging Spectrometry for Soil Applications

Abstract: Imaging spectroscopy (IS) is a new technique that has attracted the attention of many workers in many disciplines. In the field of soil science, this technology is not well developed and additional research is still required. This is in spite of the fact the soil environment has been already studied from a reflectance perspective by many workers, with much success in providing many soil properties. Going from point to image spectrometry is not only a journey from micro‐ to macroscales but also a long stage that encounters problems such as dealing with data having a low signal‐to‐noise level, contamination of the atmosphere, large data sets, the bidirectional reflectance distribution functional effect, and more. In this chapter, we attempt to explore the feasibility of IS for soil science first by reviewing the history of IS in general, and then pointing out the potential of reflectance spectroscopy for soil application in particular. We tried to understand why, although being promising, IS is not presently well developed in the soil sciences field and we provide several explanations and solutions for that. We also explore the difficulties in acquiring and processing IS data in general and for soil in particular. To illustrate the IS potentiality in soil science, we have gathered most of the authors who have worked with soil and IS technology, and provided their and other's case studies in this regard. Soil degradation (salinity, erosion, and deposition), merging IS with other remote sensing means, soil mapping and classification, soil genesis and formation, soil contamination, soil water content, and swelling soils are the issues discussed in this study. We review these case studies and analyze how IS technology can be pushed forward for soil science applications. We assume that education, exposing the technology to end users, as well as governmental involvement are the major factors that require attention in this venue. We also suggest that the IS data be provided to the end users as real reflectance and not as raw data. This is because converting the raw data into reflectance is a complicated stage that requires experience, knowledge, and specific infrastructures not available to many users. This stage stands as a barrier that impedes potential end users, inhibiting workers from trying this technique for their needs. This chapter ends with a general call to the soil science audience to extend the utilization of IS technique and compare the ability of the technique to a “giant” that still needs to wake up. We compare the evolution of the well‐developed chemometric technique used to analyze soil properties in the laboratory with the “sleeping” IS technique.

Chapter 4 Iron Dynamics in the Rhizosphere: Consequences for Plant Health and Nutrition

Abstract: Iron is an essential micronutrient for most organisms due to its role in fundamental metabolic processes. In cultivated soils, soil solution iron is mostly oxidized [Fe(III) species] unless local anoxic conditions develop. The concentration of these Fe(III) species is small in soil solution due to the low solubility of ferric oxides, oxyhydroxides, and hydroxides, which is minimal at neutral and alkaline pH. In the rhizosphere, iron concentration in the soil solution is even lower because of its uptake by aerobic organisms (plants and microorganisms), leading to a high level of competition for Fe(III). In order to face iron competition, these organisms have evolved active uptake strategies based on acidification, chelation, and/or reduction processes. Iron competition plays a major role in microbial and plant–microbe interactions in the rhizosphere. This review summarizes current knowledge on the iron status in soils and rhizospheres, and the acquisition strategies of plants and microbes. This review also shows how the dynamic interactions between soil minerals, plants, and microorganisms impact plant health and nutrition. Analysis of these complex interactions offers an interesting case study of research on rhizosphere ecology integrating different scientific expertises and approaches.

Long‐Term Cereal‐Based Rotation Trials in the Mediterranean Region: Implications for Cropping Sustainability

Abstract: With increasing global populations particularly in developing countries, and a limited or even shrinking supply of arable land, the challenge to agriculture is to meet the world's food and fiber needs without reducing the capacity of the resource base (soil and water) to enable guaranteed production for posterity and also to accommodate society's environmental and energy concerns. The issue of production sustainability is all the more acute in semi‐arid and arid regions of the world where drought and related biophysical factors create a fragile and uncertain environment for production. In the West, mainly in temperate regions, long‐term agronomic trials have been invaluable in identifying new technologies and crop management systems that have contributed to enhanced crop output that is sustainable from the biological, environmental, and economical standpoints. Many of these trials continue to guide cropping trends into the foreseeable future. The Mediterranean region has served climatic constraints to its agriculture and despite being cultivated for millennia, it is largely food deficient. Yet long‐term cropping experiments that could direct agricultural production in a sustainable manner are relatively rare, and even most of such trials are of recent vintage. This review offers a background perspective on factors related to crop, production, and subsequently examines the various multiyear cropping system/tillage trials in countries of North Africa and West Asia that border the Mediterranean. Special emphasis is given to the wide range of trials conducted in Syria by the International Center for Agriculture Research in the Dry Areas across a range of rainfall zones that are typical of the region as a whole. The goal of many trials was to identify cropping systems as a substitute for fallow and continuous cereal cropping with implications for improved water‐use efficiency (WUE), crop quality, soil quality, and fertilizer use. Lessons learned from the trials are highlighted as well as future directions for cropping systems research.

Modeling N Dynamics to Assess Environmental Impacts of Cropped Soils

Abstract: Models are useful tools to evaluate environmental impacts associated with nitrogen management in cropping systems and to predict them correctly. The purpose of this chapter was to analyze whether existing models satisfactorily simulate N losses in agroecosystems, require input data that are accessible, and can incorporate agricultural and climatic changes. The literature on 62 nitrogen models was reviewed. Each model was analyzed to identify the processes simulated, the equations used, the time and space scales, the input data and their degree of accessibility, and finally its performance. The review showed that a wide range of formalisms have been developed to model N processes. N losses such as nitrate leaching give better performance than N gas emissions, underlining the need to improve the understanding and modeling of denitrification and volatilization. It also revealed the narrow range of crop families parameterized and validated with field measurements. The main trend in modeling over the last 15 years has been the shift from mechanistic models to functional models, with a simplification of the equations involved and an aggregation of modules according to specific objectives. The more recent models have thus generally been based on specific contexts and cannot be directly extrapolated to other pedoclimatic and crop contexts, yet this is necessary for evaluating scenarios involving changes in land use and management or climatic uncertainties.

Reaction and Transport of Arsenic in Soils: Equilibrium and Kinetic Modeling

Abstract: Arsenic contamination of the soil and groundwater poses great risk to human and animal health There is a growing public interest in developing risk assessment framework, environment regulations, and remedial strategies for protecting ecosystems and human from arsenic poisoning Although extensive research efforts have been made over the past four decades, the prediction of the fate and transport of arsenic in soils are often inaccurate due to the complex biogeochemical reactions of various arsenic species in soil and water environments In-depth knowledge of factors that influence the behavior of arsenic in aqueous and solid phases are critical in making accurate determinations of the mobility, bioavailability, and toxicity of arsenic in the soil root zone In this contribution, we present a review of the state of knowledge on reactions and transport of arsenic in soils with emphasis on modeling of the physical, chemical, and biological interactions of arsenic in soil environment Specifically, we present an overview of (i) biogeochemical mechanisms of arsenic adsorption desorption, oxidation reduction, and precipitation dissolution; (ii) reactive transport mechanisms of arsenic in the natural environment as affected by factors including arsenic species, redox potential, solution chemistry, flow regime, and colloid-facilitated transport; and (iii) equilibrium and kinetic modeling approaches to simulating the geochemical reactions and transport mechanisms of arsenic in porous media A range of remedial technologies have been reviewed and their effectiveness and feasibility in the removal or in situ stabilization of arsenic in contaminated soils are discussed Future research needs are also outlined

Advances in Precision Conservation

Abstract: Population growth is expected to increase, and the world population is projected to reach 10 billion by 2050, which decreases the per capita arable land. More intensive agricultural production will have to meet the increasing food demands for this increasing population, especially because of an increasing demand for land area to be used for biofuels. These increases in intensive production agriculture will have to be accomplished amid the expected environmental changes attributed to Global Warming. During the next four decades, soil and water conservation scientists will encounter some of their greatest challenges to maintain sustainability of agricultural systems stressed by increasing food and biofuels demands and Global Warming. We propose that Precision Conservation will be needed to support parallel increases in soil and water conservation practices that will contribute to sustainability of these very intensively-managed systems while contributing to a parallel increase in conservation of natural areas. The original definition of Precision Conservation is technologically based, requiring the integration of a set of spatial technologies such as global positioning systems (GPS), remote sensing (RS), and geographic information systems (GIS) and the ability to analyze spatial relationships within and among mapped data according to three broad categories: surface modeling, spatial data mining, and map analysis. In this paper, we are refining the definition as follows: Precision Conservation is technologically based, requiring the integration of one or more spatial technologies such as GPS, RS, and GIS and the ability to analyze spatial relationships within and among mapped data according to three broad categories: surface modeling, spatial data mining, and map analysis. We propose that Precision Conservation will be a key science that will contribute to the sustainability of intensive agricultural systems by helping us to analyze spatial and temporal relationships for a better understanding of agricultural and natural systems. These technologies will help us to connect the flows across the landscape, better enabling us to evaluate how we can implement the best viable management and conservation practices across intensive agricultural systems and natural areas to improve soil and water conservation.

Chapter 5 Nanoscale Particles and Processes: A New Dimension in Soil Science

Abstract: This chapter deals with a fundamental question in soil science and environmental hydro-, bio-, and geochemistry: How do the properties and behaviors of the smallest particles—the nanoparticles—differ from those of ions and molecules, and of the larger particles whose properties are understood based on classic physics and chemistry of bulk systems? We shall see in this chapter that the nanoparticles, defined as particles that have at least one dimension in the nanorange, can have unique size-related structure, composition, stability, and reactivity. Given that nanoparticles and nanostructures are important and widespread components of soils, ranging from the nanomineral ferrihydrite, to a wide variety of mineral nanoparticles, to nanoscale aggregates of natural organic matter, to bacterial appendages known as nanowires, recent developments in nanoscience and nanotechnology are becoming increasingly important to our understanding of soil characteristics and behavior.

Sugarcane for Bioethanol: Soil and Environmental Issues

Abstract: Cultivation of sugarcane for bioethanol is increasing and the area under sugarcane is expanding. Much of the sugar for bioethanol comes from large plantations where it is grown with relatively high inputs. Sugarcane puts a high demands on the soil because of the use of heavy machinery and because large amounts of nutrients are removed with the harvest; biocides and inorganic fertilizers introduce risks of groundwater contamination, eutrophication of surface waters, soil pollution, and acidification. This chapter reviews the effect of commercial sugarcane production on soil chemical, physical, and biological properties using data from the main producing areas. Although variation is considerable, soil organic C decreased in most soils under sugarcane and, also, soil acidification is common as a result of the use of N fertilizers. Increased bulk densities, lower water infiltration rates, and lower aggregate stability occur in mechanized systems. There is some evidence for high leaching losses of fertilizer nutrients as well as herbicides and pesticides; eutrophication of surface waters occurs in high‐input systems. Soil erosion is a problem on newly planted land in many parts of the world. Trash or green harvesting overcomes many of the problems. It is concluded that sugarcane cultivation can substantially contribute to the supply of renewable energy, but that improved crop husbandry and precision farming principles are needed to sustain and improve the resource base on which production depends.

Sampling and Measurement of Ammonia at Animal Facilities

Abstract: Scientific understanding and technical control of ammonia (NH3) at animal facilities, including animal buildings, feedlots, manure storages, and manure treatment plants, depend on reliable sampling and measurement techniques to ensure high quality data that are essential to the study and abatement of NH3 emission. This chapter focuses on the methodology and technology of NH3 sampling and measurement that has been tested or applied under field conditions since the 1960s. It draws a comprehensive and updated picture of the state of the art of NH3 concentration measurement at animal facilities. Ammonia sampling requires selection of location, time, and/or control of sample volume. Three sampling methods, the closed, point, and open-path methods, are summarized. Thirty-one measurement instruments/sensors are identified. They are categorized in nine groups and evaluated according to their technical characteristics. Field studies or applications of these instruments/sensors are reviewed and summarized. Principles, procedures, advantages, and disadvantages of various sampling and measurement techniques are discussed. An overview of data and data quality is provided. Errors resulted from calibration, sampling, measurement, and data processing are discussed. Error reduction methods are presented. Recommendations are made for selection of sampling methods and measurement devices and for future needs including development of methodologies and standards.

Genetic improvement of forage species to reduce the environmental impact of temperate livestock grazing systems.

Abstract: The livestock agriculture of temperate grasslands is a major provider of meat and milk to the world. These areas also deliver important ecosystem services and are central to tourism, amenity, and leisure in many countries. However, they are also major sources of pollution of waterways and of greenhouse gas emissions. In this review, we focus on how the genetic improvement of some of the major crop species of temperate grasslands can contribute to reduced environmental impacts and climate change mitigation including the enhancement of carbon sequestration. The main species considered are the ryegrasses and fescues and the clovers. With regard to diffuse pollution of waterways, increasing the efficiency with which the plant utilizes nitrogen and phosphorus has significant potential to reduce the amounts available for leaching and overland flow. This also allows reduced fertilizer use, in itself representing a significant saving of greenhouse gas emissions. Changes in the composition of the plant diet have the potential to increase the efficiency of nitrogen use in the rumen and reduce the amount of methane produced by enteric fermentation. Carbon sequestration in temperate grasslands may potentially be enhanced by understanding and altering root architecture and turn over and also litter composition. The role of forage breeding in improving soil quality and flood defense is also considered and wider aspects of the role of persistent perennial species discussed. To fully realize the potential of genetic improvement, breeding programs need to incorporate state-of-the-art genomics and also to be guided by modeling studies. An integrated approach combining the skills of animal scientists, soil scientists, and plant breeders within the context of life cycle analysis is required to find sustainable solutions to the challenge of maintaining the productivity of livestock agriculture while reducing its environmental footprint.

Chapter 6 Advances in Isotopic Dilution Techniques in Trace Element Research: A Review of Methodologies, Benefits, and Limitations

Abstract: New insights into factors controlling element bioavailability and mobility in soils have been achieved through the use of isotopic dilution methods. With the advent of robust and relatively simple analytical techniques able to accurately determine stable isotope ratios, the future use of isotopic dilution methods is expected to continue to expand. In both theory and practice, the E‐ and L‐value isotopic dilution methods appear relatively simple to apply. However, this simplicity is deceptive: in reality, there exist a number of pitfalls that can result in collection of flawed data or inappropriate data interpretation. With a focus on trace elements, this chapter reviews studies that have applied isotopic dilution techniques to examine various aspects of soil chemistry and bioavailability, provides guidance on conducting isotopic dilution experiments, and discusses potential future applications for these techniques. The various pitfalls that may be encountered, including precipitation artifacts, colloidal interferences, and labile redox state effects, as well as how to identify and avoid such pitfalls, are also described.

The role of scientists in multiscale land use analysis: lessons learned from Dutch communities of practice

Abstract: Many research and scientific organizations emphasize the importance of science for society in their strategic plans. This is certainly true for land use studies being discussed in this chapter as new environmental policies are introduced at European and national level. Such policies reflect concerns of society so that a structural link between science and policymaking would appear to be logical and desirable. Rather than following traditional top‐down and disciplinary research approaches, emphasis is increasingly being placed on interactive, interdisciplinary work in Communities of Practice (CoPs) in which scientists work together with various stakeholders and policymakers in a joint learning mode. But this requires new research approaches including long‐term engagement during the entire policy cycle asking for a new attitude of scientists. Few experiences have been reported so far. Three Dutch case studies are therefore discussed to illustrate the functioning of CoPs by focusing on up‐ and downscaling (called multiscaling hereafter), a key element of land use research. Five types of multiscaling were used in the three case studies. Three were technical: (1) use of model‐ or design‐based (geo)statistical techniques, (2) extrapolation of data obtained from experimental plots to larger areas, and (3) use of quasi‐3D process models to upscale grid data in a Geographic Information System (GIS) to regions. Two were policy oriented: (1) nutrient balances for farms to allow upscaling from fields to farm and (2) a research framework for regions, based on the DPSIR approach, which sequentially covers aspects mentioned in environmental laws as being important for sustainable development. Quite diverse and unrelated questions about land use issues by different members of the CoP cannot be a fruitful basis for research programs. Scientists have therefore an important role to play within a CoP in orchestrating a demand analysis that puts questions into context and defines existing knowledge as well as knowledge gaps. Defining research on the basis of a demand analysis in a CoP creates innovative ideas, creates commitment of participants, and allows definition of needed research that is functional. This includes cutting edge research publishable in literature and requires for land use studies updating of valuable existing soil survey information to a level that can be used in modern modeling techniques including functional characterization of soil series, development of pedotransfer functions, and definition of phenoforms. Particular attention is needed for introducing modern monitoring techniques for soil and water because the high cost of traditional methods implies that little monitoring is done now with detrimental effects for the calibration and validation of simulation models that increasingly secure a live of their own. The scientific community needs to take a fresh look at its paradigms. Next to the establishment of CoPs, we therefore advocate development of Communities of Scientific Practice (CSP) within the research community that define different functions for members of the scientific community in terms of (1) communication within CoPs by shaping the demand analysis and to the outside world and (2) defining research needs and its execution, using knowledge chains including basic research.

Succession of Arbuscular Mycorrhizal Fungi: Patterns, Causes, and Considerations for Organic Agriculture

Abstract: Arbuscular mycorrhizal fungi (AMF) have been promoted as a biofertilizer for sustainable agriculture, and production of inoculum is a widespread and growing industry. The last decade of AMF research has revealed far more selectivity of AMF community association with their hosts and a greater dependence of resulting functions on particular host/fungus combinations than previously imagined, with the effects of specific host/AMF combinations ranging from beneficial to parasitic; hence, the next step in AMF application will entail an effort toward employing beneficial combinations. AMF communities and abundances may fluctuate throughout seasons and years, for example, because of changes in the abiotic and biotic environments. To date, we have little information on the persistence of applied AMF in systems and how changes in the AMF community through time may affect plant growth. We must consider how to manage the soil environment to direct succession of AMF species and the displacement of applied or beneficial AMF. This chapter attempts to merge our current understanding of AMF succession from natural ecosystems with that of AMF application in agriculture. We discuss the patterns and causes of change in AMF abundance and species compositions through time, considering how common organic farming techniques may affect these fungi. We propose that management techniques could be employed to direct AMF succession and maintain specific, beneficial species or species groups, with the potential to increase the sustainability and benefits derived from AMF in organic agriculture.

Chapter 5 Geochemistry of Green Rusts and Fougerite: A Reevaluation of Fe cycle in Soils

Abstract: The oxidation state of Fe in soils plays an important role in determining the mobility of Fe in soil solutions, and the mineralogy of iron oxides. The purpose of this chapter is to review the state of the art regarding Fe cycle in soils, protocols for studying the redox state of iron in soils and soil solutions, the recent data obtained on the natural green rust, fougerite, and the consequences of the reactivity of this mineral on the coupling of iron and other elements' cycles.

Soil Structure: A History from Tilth to Habitat

Abstract: Publisher Summary This chapter concentrates on the thread of the changing concepts and studies of soil structure. The chapter examines the approaches to soil structure, based on writings from five periods in the past two millennia. While the dates are somewhat flexible, periods of different thinking can be distinguished. The early concept of soil structure was soil tilth, stirring the soil to prepare a seedbed consisting of small aggregates. Soil aggregates, aggregation, and field description of soil structure were described during 1930 to 1950. Aggregation and tilth, soil structure and soil erosion, soil mechanics studies of soil structure, and soil compaction were described during 1950 to 1980. Structure as habitat for biota has revitalized the study of soil structure. These studies are led largely by soil biologists and landscape ecologists. Knowledge about soils was developed, in its early history, by practitioners who worked with soils. This knowledge was related to the social conditions of the times and to society's needs. With the advent of soil science laboratories, the dominant concern soon became measurement of static properties relating to tilth and stability of structure: aggregate-size distribution, porosity, grain-size distribution, stability of aggregates, shape, and size of aggregates. The importance for soil structure of organic matter and of clay content was generally recognized. All these properties were studied in relation to cultivation and to the effects of cultivation on tilth and yield. The concept of hierarchical arrangement of different aggregate sizes, and the bonds responsible for stability, drew attention to different void sizes and to the soil functions of each.

Chapter 2 Uptake and Fate of Perchlorate in Higher Plants

Abstract: Perchlorate recently emerged as a drinking water contaminant, and its high water solubility and relatively unreactive nature under ambient conditions make it a persistent and mobile contaminant Perchlorate interferes with iodine uptake by the human thyroid, potentially leading to adverse effects on normal metabolism and cognitive function in sensitive groups There is an interest in the fate of perchlorate in higher plants because phytoremediation is a promising remediation option, and because there is mounting concern about human exposure to perchlorate from contaminated produce Perchlorate is taken up by many higher plants and is mainly stored in leaves, although perchlorate is also found in smaller quantities in fruits, stems, seeds, and roots Transpiration plays a key role in delivery of perchlorate to plant roots, and it appears that perchlorate traverses the root cell membrane via the same ion transporter as for nitrate Certain plants are able to metabolize high concentrations (mg/liter) of perchlorate within their leaves (phytodegradation) by way of chlorate and chloride intermediates to chloride, although this process is slower than ex situ microbial degradation in the root zone (rhizodegradation) However, it is currently unknown whether higher plants will metabolize smaller quantities (ie, μg/liter concentrations) of perchlorate in vivo More research is needed in order to determine the extent of translocation, phytodegradation, and exudation of perchlorate and its metabolites, as well as the ability of modified stems and roots to store perchlorate

Influence of Coupled Processes on Contaminant Fate and Transport in Subsurface Environments

Abstract: The following chapter emphasizes subsurface environmental research investigations over the past 10 to 15 years that couple hydrological, geochemical, and biological processes as related to contaminant fate and transport. An attempt is made to focus on field‐scale studies with possible reference to laboratory‐scale endeavors. Much of the research discussed reflects investigations of the influence of coupled processes on the fate and transport of inorganic, radionuclide, and organic contaminants in subsurface environments as a result of natural processes or energy and weapons production endeavors that required waste disposal. The chapter provides on overview of the interaction between hydro‐bio‐geochemical processes in structured, heterogeneous subsurface environments and how these interactions control contaminant fate and transport, followed by experimental and numerical subsurface science research and case studies involving specific classes of inorganic and organic contaminants. Lastly, thought provoking insights are highlighted on why the study of subsurface coupled processes is paramount to understanding potential future contaminant fate and transport issues of global concern.

Mutagenesis and High‐Throughput Functional Genomics in Cereal Crops: Current Status

Abstract: The accumulation of large sequence information in cereal crop plants has opened opportunities for determining gene function using reverse genetics rather than forward‐genetics approaches. A number of reverse‐genetics approaches have been developed and used in model plant species such as Arabidopsis and rice and recently been extended to other cereal crop species during the last few years to determine gene‐function relationship. Insertional and chemical/physical mutagen induced mutagenesis combined with emerging high‐throughput analytical approaches have made it possible to rapidly discover sequence‐function relationship through reverse genetics at genome‐wide scale, even in large genome cereal species. In this review, we provide a brief glimpse of the insertional mutagenesis (T‐DNA and transposons) based approaches and thereafter discuss the recently discovered non‐transgenic technologies such as TILLING (Targeting Induced Local Lesions IN Genomes) and DEALING (Detecting Adduct Lesions In Genomes), and their emerging applications in cereal crop plants using suitable examples.

Contaminants as Tracers for Studying Dynamics of Soil Formation: Mining an Ocean of Opportunities.

Abstract: Contaminants as Tracers for Studying Dynamics of Soil Formation: Mining an Ocean of Opportunities.

Chapter 3 Epigenetics. The Second Genetic Code

Abstract: Plant breeders utilize directed selection and transgenics to produce novel cultivars of diploid and polyploid species. DNA sequence is clearly important in these processes, but growing evidence implicates epigenetics as an important factor in controlling genetic variation and gene/transgene expression. In this article, we focus on epigenetic variation defined as mitotically and meiotically heritable but reversible states of gene expression that are not conditioned by differences in DNA sequence. We summarize mechanisms underlying epigenetic states of expression, and discuss implications of epigenetics in cultivar development.

Chapter 1 Dr. Norman E. Borlaug: Twentieth Century Lessons for the Twenty‐First Century World

Abstract: In all history, only five persons have received the Nobel Peace Prize, the Presidential Medal of Freedom and the Congressional Gold Medal. Norman Borlaug is one. The others are Mother Teresa, Nelson Mandela, Elie Wiesel, and Dr. Martin Luther King. The Congressional Gold Medal was the capstone of an extraordinary journey that began on an Iowa farm in 1914 and that took Borlaug to the University of Minnesota, hardscrabble farm fields of Mexico, famine threatened areas of India and Pakistan, poverty‐stricken villages of Africa, the faculty of Texas A&M University, the White House to accept the National Medal of Science, and eventually back to Iowa to establish the World Food Prize. Named by TIME Magazine as one of the 100 most influential minds of the twentieth century, Borlaug labored in Mexico for 13 years developing a rust‐resistant wheat variety that dramatically increased yields. In the immediate aftermath of World War II, the specter of mass starvation haunted the Indian subcontinent. But, India and Pakistan were pulled back from enormous human tragedy by the pioneers who ushered in the Green Revolution. Norman Borlaug was presented the Nobel Peace Prize in 1970 for leading this effort. One of Norman Borlaug's most lasting contributions may be the creation of the World Food Prize to further inspire such breakthrough achievements. It would be only fitting if Borlaug's twentieth century accomplishments would be the vehicle that brought peace and reconciliation to a deeply troubled twenty‐first century world.