Showing papers in "Advances in Agronomy in 2005"

Enhancing nitrogen use efficiency in crop plants

Abstract: Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops

Efficiency of Fertilizer Nitrogen in Cereal Production: Retrospects and Prospects

Abstract: Presently, 50% of the human population relies on nitrogen (N) fertilizer for food production. The world today uses around 83 million metric tons of N, which is about a 100‐fold increase over the last 100 years. About 60% of global N fertilizer is used for producing the world's three major cereals: rice, wheat, and maize. Projections estimate that 50 to 70% more cereal grain will be required by 2050 to feed 9.3 billion people. This will require increased use of N of similar magnitude if the efficiency with which N is used by the crop is not improved. Fertilizer N‐recovery efficiency by the first crop is 30 to 50%. The remaining N either remains in the soil, the recovery of which in the following crops is very limited (

The Contribution of Breeding to Yield Advances in maize (Zea mays L.)

Abstract: Maize (Zea mays L.) yields have risen continually wherever hybrid maize has been adopted, starting in the U.S. corn belt in the early 1930s. Plant breeding and improved management practices have produced this gain jointly. On average, about 50% of the increase is due to management and 50% to breeding. The two tools interact so closely that neither of them could have produced such progress alone. However, genetic gains may have to bear a larger share of the load in future years. Hybrid traits have changed over the years. Trait changes that increase resistance to a wide variety of biotic and abiotic stresses (e.g., drought tolerance) are the most numerous, but morphological and physiological changes that promote efficiency in growth, development, and partitioning (e.g., smaller tassels) are also recorded. Some traits have not changed over the years because breeders have intended to hold them constant (e.g., grain maturity date in U.S. corn belt). In other instances, they have not changed, despite breeders' intention to change them (e.g., harvest index). Although breeders have always selected for high yield, the need to select simultaneously for overall dependability has been a driving force in the selection of hybrids with increasingly greater stress tolerance over the years. Newer hybrids yield more than their predecessors in unfavorable as well as favorable growing conditions. Improvement in the ability of the maize plant to overcome both large and small stress bottlenecks, rather than improvement in primary productivity, has been the primary driving force of higher yielding ability of newer hybrid.

Labile Organic Matter Fractions as Central Components of the Quality of Agricultural Soils: An Overview

Abstract: Total soil organic matter content is a key attribute of soil quality since it has far-reaching effects on soil physical, chemical, and biological properties. However, changes in contents of organic carbon (C) and total nitrogen (N) occur only slowly and do not provide an adequate indication of important short-term changes in soil organic matter quality that may be occurring. Labile organic matter pools can be considered as fine indicators of soil quality that influence soil function in specific ways and that are much more sensitive to changes in soil management practice. Particulate organic matter consists of partially decomposed plant litter, and it acts as a substrate and center for soil microbial activity, a short-term reservoir of nutrients, a food source for soil fauna and loci for formation of water stable macroaggregates. Dissolved (soluble) organic matter consists of organic compounds present in soil solution. This pool acts as a substrate for microbial activity, a primary source of mineralizable N, sulfur (S), and phosphorus (P), and its leaching greatly influences the nutrient and organic matter content and pH of groundwater. Various extractable organic matter fractions have also been suggested to be important, including hot water-extractable and dilute acid-extractable carbohydrates, which are involved in stabilization of soil aggregates, and permanganate-oxidizable C. Measurement of potentially mineralizable C and N represents a bioassay of labile organic matter using the indigenous microbial community to release labile organic fractions of C and N. Mineralizable N is also an important indicator of the capacity of the soil to supply N for crops. It is concluded that individual labile organic matter fractions are sensitive to changes in soil management and have specific effects on soil function. Together they reflect the diverse but central effects that organic matter has on soil properties and processes. (c) 2005 Elsevier Inc.

Pre‐Sowing Seed Treatment—A Shotgun Approach to Improve Germination, Plant Growth, and Crop Yield Under Saline and Non‐Saline Conditions

Abstract: Rapid seed germination and stand establishment are critical factors to crop production under salt‐stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to salinity stress. Salinity may delay the onset, reduce the rate, and increase the dispersion of germination events, leading to reductions in plant growth and final crop yield. The adverse effects of salt‐stress can be alleviated by various measures, including seed priming (a.k.a. pre‐sowing seed treatment). The general purpose of seed priming is to partially hydrate the seed to a point where germination processes are begun but not completed. Most priming treatments involve imbibing seed with restricted amounts of water to allow sufficient hydration and advancement of metabolic processes but preventing germination or loss of desiccation tolerance. Treated seeds are usually redried before use, but they would exhibit rapid germination when re‐imbibed under normal or stress conditions. Various seed priming techniques have been developed, including hydropriming (soaking in water), halopriming (soaking in inorganic salt solutions), osmopriming (soaking in solutions of different organic osmotica), thermopriming (treatment of seed with low or high temperatures), solid matrix priming (treatment of seed with solid matrices), and biopriming (hydration using biological compounds). Each treatment has advantages and disadvantages and may have varying effects depending upon plant species, stage of plant development, concentration/dose of priming agent, and incubation period. In this article, we review, evaluate, and compare effects of various methods of seed priming in improving germination of different plant species under saline and non‐saline conditions. We also discuss the known metabolic and ultra‐structural changes that occur during seed priming and subsequent germination. To maximize the utility of various seed priming techniques, factors affecting their efficiency must be examined and potential benefits and drawbacks determined. For example, quality of the seed before treatment, concentration/dose of priming agent, time period for priming, and storage quality of the seed following priming treatment must be carefully determined. Furthermore, such assessments must be based on large‐scale experiments if seed priming is to be used for large‐scale field planting. A better understanding of the metabolic events that take place in the seed during priming and subsequent germination will improve the effective application of this technology. The incorporation of advanced molecular biology techniques in seed research is vital to the understanding and integration of multiple metabolic processes that can lead to enhanced seed germination, and consequently to improved stand establishment and crop yield under saline and non‐saline conditions.

Antibiotic Use in Agriculture and Its Impact on the Terrestrial Environment

Abstract: Since their discovery, antibiotics have been instrumental in treating infectious diseases that were previously known to kill humans and animals. However, their widespread use as an additive in animal feeds has raised concerns about the development of antibiotic‐resistant microorganisms. Increasingly, more microorganisms are becoming resistant to multiple antibiotics. A high proportion of the antibiotics added to animal feed is excreted in urine or manure. In some cases, as much as 90% of the antibiotic administered orally may pass through the animal unchanged. Once excreted in urine and manure, these antibiotics can enter surface and/or groundwater through nonpoint source pollution from manure‐applied lands. The literature shows that most of the antibiotics are strongly adsorbed in soils and are not readily degraded. An important environmental concern is the presence of antibiotics in sources of potable water. Except erythromycin and some sulfa drugs, most of the antibiotics found in surface waters have been only in minute quantities. In all cases, the amounts observed are in parts per billion ranges; 100‐ to 1000‐fold below minimum inhibitory concentration. Tetracyclines and penicillins, two of the most commonly used antibiotics in animal agriculture, have seldom been found in sources of potable water. There has been some reported presence of resistant bacteria in surface waters. This may have been from transport of resistant bacteria via animal or insect vectors, in airborne dusts, or simply water flow from some antibiotic‐rich setting such as manure lagoons. Direct toxic effects of antibiotics on plants and soil microflora and ‐fauna are unlikely because of the low concentrations at which antibiotics in manure are land‐applied. The indirect effects of antibiotics on the food web, however, cannot be discounted at this stage. Decrease in some components of the soil microbial populations due to manure‐applied antibiotics could cause loss of food sources for other soil organisms, which, in turn, could affect important soil microbial processes such as decomposition and mineralization. Also, repeated application of antibiotic‐laden manure can provide an environment in which selection of antibiotic‐resistant bacteria can occur. Prudent use of antibiotics to a bare minimum along with alternative methods that minimize development and proliferation of resistant bacteria need investigation.

The Depth Distribution of Soil Organic Carbon in Relation to Land Use and Management and the Potential of Carbon Sequestration in Subsoil Horizons

Abstract: Routine soil surveys for estimating the soil organic carbon (SOC) pool account for a soil depth of about 1 m Deeper soil horizons, however, may have a high capacity to sequester significant amounts of SOC as the turnover time and chemical recalcitrance of soil organic matter (SOM) increases with depth The subsoil carbon (C) sequestration may be achieved by higher inputs of fairly stable organic matter to deeper soil horizons This can be achieved directly by selecting plants/cultivars with deeper and thicker root systems that are high in chemical recalcitrant compounds like suberin Furthermore, recalcitrant compounds could be a target for plant breeding/biotechnology to promote C sequestration A high surface input of organic matter favors the production of dissolved organic carbon that can be transported to deeper soil horizons and thus contribute to the subsoil C storage By promoting the activity of the soil fauna, organic matter can be transferred to deeper soil layers and stabilized (eg, in earthworm casts) Manipulating the subsoil microorganisms may result in higher amounts of fairly stable aliphatic compounds The subsoil below 1‐m depth may have the potential to sequester between 760 and 1520 Pg C These estimates are, however, highly uncertain and more studies on C storage in subsoil horizons and the assessment of the chemical nature of subsoil organic C are needed

Crop residue management for nutrient cycling and improving soil productivity in rice-based cropping systems in the tropics

Abstract: Publisher Summary Crop residues, usually considered a problem, when managed correctly can improve soil organic matter dynamics and nutrient cycling, thereby creating a rather favorable environment for plant growth. The intelligent management and utilization of crop residues is essential for the improvement of soil quality and crop productivity under rice-based cropping systems of the tropics. Viable option is to retain residue in the field; burning should be avoided. The major issue is adapting drills to sow into loose residues. Strategies include chopping and spreading of straw during or after combining or the use of disc-type trash drills. Residues rich in lignin and polyphenol contents experience the lowest decay. Decomposition of crop residues occurs at a rapid rate—about 80% of crop residue C is lost in the first year—under the warm and humid conditions of the tropics. Factors that control C decomposition also affect the N mineralization from the crop residues. Decomposition of poor-quality residues with low N contents, high C:N ratios, and high lignin and polyphenol contents generally results in microbial immobilization of soil and fertilizer N. Nutrient cycling in the soil–plant ecosystem is an essential component of sustainable productive agricultural enterprise. Although during the last three decades, fertilization practices have played a dominant role in the rice-based cropping systems, crop residues—the harvest remnants of the previous crop still play an essential role in the cycling of nutrients. Incorporation of crop residues alters the soil environment that in turn influences the microbial population and activity in the soil and subsequent nutrient transformations.

Nutrient stocks, nutrient cycling and soil changes in cocoa ecosystems - a review

Abstract: It is generally assumed that agricultural systems with perennial crops are more sustainable than systems with annual crops. Soil erosion is negligible and perennial crops have more closed nutrient cycling. Moreover, inorganic fertilizers are used more commonly in cash crops such as perennial crops so that soil fertility decline and nutrient mining are less likely to occur. In the past decades, considerable research has been devoted to the quantification of nutrient stocks and nutrient cycling in agro-ecosystems. This article reviews the main stocks and flows of nutrients in cocoa ecosystems for several cocoa-growing regions in the tropics. Most of the nitrogen is found in the topsoils, and less than 10% of the total N stock is in the cocoa and shade trees. Nitrogen in the annual litter fall is about 20 to 45% of the total N in the vegetation and 2 to 3% of the total N in the soil. The accumulation of potassium is low in cocoa ecosystems, and in most systems the total amount in the biomass is equivalent to the available P content in the topsoil. Phosphorus in the annual litter fall is about 10 to 30% of the total P in the vegetation and 10 to 40% of the available P in the soil. Potassium is a major nutrient in mature cocoa. Stocks of exchangeable K in the topsoil vary from 100 to 550 kg ha −1 , and high K levels in the soil correspond to high K levels in the vegetation and litter. Partial nutrient balances were calculated that compares the losses, addition, and transfer of N, P, and K. The nutrient balance is negative in the absence of inorganic fertilizers, especially for K. Rainwash and litter fall are key components in the cycling of nutrients of cocoa ecosystems. The amount of nutrients transferred by rainwash is less than 8 kg ha −1 for N and P but varies from 38 to more than 100 kg ha −1 year −1 for K. Most soils under cocoa had a lower fertility when compared to primary forest, although soil chemical properties seem to settle at equilibrium levels. This review shows that large amounts of nutrients in cocoa ecosystems are transferred each year and that such nutrient cycling is essential for maintaining cocoa production.

Interactions of Nitrogen with Other Nutrients and Water: Effect on Crop Yield and Quality, Nutrient Use Efficiency, Carbon Sequestration, and Environmental Pollution

Abstract: Publisher Summary Nitrogen, which is required in the greatest quantity of all mineral nutrients absorbed by plant roots, is an essential component of protein. The long-term strategy of nitrogen (N) use in agriculture likely will involve increased reliance on fertilizer N, biological N fixation (BNF) by leguminous crops, and wastes (including farm, urban, and industrial wastes) and their efficient management. The amounts of different nutrients absorbed by a crop from soil may vary 10,000-fold, from 200 kg of N ha-1 to less than 20 g of Mo ha-1, and yet rarely do these nutrients work in isolation. As N function in plant growth and nutrition is closely connected to C, the C=N ratio controls N availability. Nutrient interactions have a role to play in determining the course and outcome of two major issues of interest in fertilizer management—namely, balanced fertilizer input and efficient fertilizer use. The N x P (phosphorus) interaction can be termed the single most important nutrient interaction of practical significance. In addition to N, potassium (K) is the major plant nutrient absorbed and removed by crops in the largest amounts among all essential nutrients. Sulfur (S) is the fourth major fertilizer nutrient along with N, P, and K. The deficiency of S has been reported with increasing frequency in the past several years all over the world. Although Ca requirements for plant growth and metabolism are low—it has great significance in balancing levels of other nutrients—including N. Deficiencies of different micronutrients can result in a serious reduction in grain yield and quality of crops, and utilization efficiency of other nutrients and water. These include zinc, copper, manganese, iron, boron, cobalt, and molybdenum. Also, water and N are the most important factors controlling crop growth and grain production.

Advances in Hydropedology

Abstract: Hydropedology is an intertwined branch of soil science and hydrology that encompasses multiscale basic and applied research of interactive pedological and hydrological processes and their properties in the unsaturated zone. The synergistic integration of classical pedology with soil physics, hydrology, and other related bio- and geosciences into hydropedology suggests a renewed perspective and a more integrated approach to studying landscape–soil–water dynamics across scales. Pedality, layering of soil horizons, and soil–landscape relationships are three essential characteristics of soils as occurring on the landscape. Fundamental issues of hydropedology include (1) soil structure and layering as indicators of flow and transport characteristics in field soils; (2) soil morphology as signatures of soil hydrology; (3) water movement over the landscape; and (4) hydrology as a factor of soil formation and a driving force of dynamic soil system. Hydrology affects and is affected by all of the five natural soil-forming factors and the four general soil-forming processes. Hence, hydropedology offers potential opportunities for quantifying soil-forming processes. Future needs in advancing hydropedology are encapsulated in the philosophy of “bridging disciplines, scales, data, and education.” These include (1) systems approaches to understanding and communicating landscape–soil–water dynamics; (2) addressing variability using patterns at various scales; (3) enhancing pedotransfer functions and developing soil inference systems and hydropedoinformatics; and (4) education of the next generation of soil scientists and hydrologists. Hydropedology calls for adequate attention to soil morphology (including soil structure) in the field and soil patterns over the landscape to guide optimal soil physical and hydrological measurements, field monitoring and experimental designs, and understanding and modeling of flow and transport in the critical zone. Identification and prediction of patterns (spatial-temporal organizations) across multiple scales are coming to the forefront in soil science and hydrology, which offer rich and comprehensive insights regarding variability and the underlying processes. We suggest various hydropedological approaches to address diverse knowledge gaps. Given its links to a wide array of environmental, ecological, geological, agricultural, and natural resource issues of societal importance, hydropedology is emerging as a promising field that could contribute significantly to the study of the pedosphere, the hydrological cycle, the earth's critical zone, and the earth system.

Rice–Wheat Cropping Systems

Abstract: Publisher Summary According to the International Food Policy Research Institute, between 1993 and 2020 A.D. the global demand for cereals is expected to increase by 41%. It has been projected that annual rice production must increase from 556 million tons in 2000 A.D. to 758 million tons by 2020 A.D., a 36% increase. Rice-wheat cropping system (RWCS) is a long-established grain production system in China. The wheat yield following rice was only 0.7 to 1.0 tons ha-1 until the 1940s and it increased progressively after the 1950s as a result of improved varieties, better agronomic management, and pest control. RWCS in the Indian subcontinent is quite new and started only in the late 1960s with the introduction of dwarf wheat from CIMMYT, Mexico, which required a lower temperature for good germination than that required for traditional tall Indian wheat. There could be many more variants involving vegetables and other short duration crops. Most rice in RWCS is transplanted and rice varieties grown are of 90–140 days duration (seed to seed) of which 25–45 days may be spent in nursery. The estimates of area under RWCS in the world vary considerably. In RWCS there is very little turn-around time between rice harvest and wheat sowing. Depending on the time of harvest of the rice crop, conventional tillage requires pre-sowing irrigation on well-drained soils or draining or drying of soil in lowlands followed by one or two diskings, two harrowings, and leveling. Wheat in the RWCS belt in Indo-Gangetic Plains (IGP) is an irrigated crop. Considerable research has been conducted in India on the irrigation of wheat. Currently, there is a growing concern in sustainability of RWCS as the growth rates of rice and wheat yields are either stagnant or declining. Studies on socioeconomic and policy factors on the productivity of RWCS will be effective for measuring outcome of RWCS.

Forage Chicory (Cichorium intybus L.): A Review of Its Agronomy and Animal Production

Abstract: Chicory (Cichorium intybus L.) is a perennial herb that has been used as a forage for livestock in many parts of the world. Forage chicory produces a large quantity of high quality feed in the warm season under favorable conditions. Animal performance on chicory is similar to that on legumes and superior to grass‐based pastures. In addition, grazing chicory can decrease some internal parasites in livestock, and therefore has potential to reduce the use of anthelmintics. Being a deep‐rooted perennial herb, chicory can reduce nitrate leaching, deep drainage, thereby reducing the rate of soil acidification and the occurrence of dryland salinity. This paper reviews the published research work on the agronomic characteristics, herbage production, grazing management, persistence under grazing, nutritive value, and animal performance of forage chicory, as well as the problems encountered when incorporating chicory into farming systems.

Metabolic Engineering of Isoflavone Biosynthesis

Abstract: Isoflavones are phenolic secondary metabolites found mostly in legumes. These compounds play key roles in many plant–microbe interactions and are associated with the health benefits of soy consumption. Because of their biological activities, metabolic engineering of isoflavonoid biosynthesis in legume and nonlegume crops have significant agronomic and nutritional impact by enhancing plant disease resistance and providing dietary isoflavones for the improvement of human health. This review first outlines the current understanding of isoflavone biosynthetic pathways, with focus on key structural enzymes and transcription factors that directly relate to the pathways. Then it summarizes recent progress on metabolic engineering of isoflavone biosynthesis in both legume and nonlegume plants. The major limitations of these approaches, as well as the “metabolic channeling” theory, which is proposed to explain some of the results from the engineering works, are also discussed.

Oxygation unlocks yield potentials of crops in oxygen-limited soil environments

Abstract: Subsurface drip irrigation (SDI) offers well‐documented potential for improving water use efficiency in irrigated agriculture. However, SDI in common with other forms of irrigation is liable to exclude soil air (and therefore oxygen) around the root zone during and following irrigation events, thus reducing root function and crop performance. When SDI is practiced with oxygation (i.e., aerating the rhizosphere by way of the irrigation stream) it could transform the irrigation industry, for it provides a source of oxygen in a root environment that suffers from temporal hypoxia, and occasionally from anoxia. The oxygen is introduced into the irrigation stream by way of the venturi principle, or with solutions of hydrogen peroxide. Oxygation assures optimal root function, microbial activity, and mineral transformations, and leads to enhanced yield and water use efficiency under hypoxic conditions. It also improves plant performance and yield under irrigated conditions previously considered to be satisfactory for crop growth, and offers scope to offset some of the negative impacts of compaction and salinity, related to poor soil aeration, on crop growth. Representing minimal capital investment and recurrent costs, economic returns appear very favorable, as do associated benefits to the environment, measured as reduced drainage, containment of rising water tables, better nutrient use efficiency, and reduced demand by agriculture for irrigation water. The aeration status of irrigated soils deserves more attention than it has received in the past if we wish to unlock yield potential constrained by soil oxygen limitations and eVect the yield increases essential to keeping pace with future food (and fibre) demand.

Assessing the Potential for Pathogen Transfer from Grassland Soils to Surface Waters

Abstract: Contamination of surface waters with pathogenic micro-organisms is an area of growing importance in the context of diffuse agricultural pollution. Hydrological pathways linking farmed land to receiving waters may operate as vectors of disease transmission. Runoff from grassland systems may be particularly important. In this chapter, we synthesize and evaluate recent and contextual studies relating to the issue. The chapter is necessarily wide ranging and interdisciplinary but we have focused largely on the hydrological, soil-based, and microbiological perspectives. The potential for pathogen presence in livestock wastes is demonstrated through prevalence studies, and subsequent loading of grasslands with contaminated wastes generates a potential surface store of pathogens. These microbes may then be transferred to the wider environment when source and transport drivers are combined in, for example, precipitation events. The delivery of contaminated agricultural drainage waters into first order streams may impact the quality and ecological balance of watercourses if the micro-organisms of concern are still viable. This chapter evaluates both die-off and transfer processes operating from source through to the end point receptors in surface waters. Gaps in knowledge are identified and appear to be due to the contribution of heterogeneity and hydrological complexity of agricultural catchments and the complications of prevalence data derived via a range of methodologies.

Bioindustrial and Biopharmaceutical Products Produced in Plants

Abstract: Over the past several years there have been many advances in plant biotechnology that have led to the successful commercialization of agricultural products for crop improvement. Plant biotechnology is now being considered as a tool to produce non-food products such as biopharmaceuticals and bioindustrial products. This chapter reviews the status of the field with particular emphasis on different plant systems. Key factors such as transformation, expression, growth, harvest, transport, storage, processing, and purification of the plant material are included. The chapter also evaluates the characteristics of different systems and their utility for different types of products. While no one system stands out as the ideal platform, this chapter does point to systems that have broader appeal and speculates as to future platforms and utilities.

Developing Existing Plant Root System Architecture Models to Meet Future Agricultural Challenges

Abstract: Improving our understanding of the relationships between soil conditions and plant growth, both above and below ground, will contribute to the development of cropping systems that are less reliant on mineral fertilizers for crop nutrition. Although many models predicting the flows of nutrients between plants and soil have been developed, few of these deal in detail with root architecture and dynamics. In this chapter, we review seven widely cited models of root architecture and development in terms of their ability to improve predictions of plant and soil nutrient flows. We have examined processes related to root system architecture and development, compared mathematical expressions and parameters used in the selected models, and summarized common processes and parameters for simulating root systems. This outcome should benefit researchers and model developers, preventing the need to spend limited resources on repeating the same process. Detailed conclusions include the fact that both inter-branching distance and insertion angle are essential parameters for representing root architecture. Additionally, in a three-dimensional model an extra parameter, radial angle, should be used for determining the location of a branch relative to the root from which it originated. Root growth is simulated by elongation rate and elongation direction, with root component diameter also represented in some models. Almost all the three-dimensional models reviewed calculate the current direction of newly formed root segments using the previous direction of tip extension together with an angle related to geotropism. This review was carried out as the first stage in a research program on integrating root growth models with soil nutrient cycling models. For this purpose, the review suggests that, in order to optimize practical applications of these models in cropping systems, there is a need to integrate a number of additional processes, including root longevity and mortality, environmental responses, and effects of management such as tillage or the pesticide application regime. The form of root mortality relevant to nutrient cycling in soil is that due to natural senescence of root components. This differs from catastrophic death of roots due to attack by pathogenic fungi, which has been considered in one existing root model. To achieve the required objectives, there is also a need to strengthen the integration of above-ground plant component dynamics with root system development, particularly in relation to breeding new crop varieties for sustainable agricultural systems.

Biological Control of Weeds with Antagonistic Plant Pathogens

Abstract: Many research programs have studied different aspects of the use of antagonistic plant pathogens in biological weed control strategies. The study of effects of individual environmental factors can be regarded as the first step in understanding limitations to the success of biological control methods. This review attempts to address the current advances of the basis and the progress of biocontrol methods, the link between environmental factors and plant infection development, and the use of formulation technology in biological weed control.

Soil Scientists in a Changing World

Abstract: Publisher Summary Science and technology in situ has changed its course along with social and economic developments. Although it has not always been beneficial to human beings, civilization has got the required mileage to drive information, culture, resources, and wealth throughout the world from one era to another. The awareness of soil goes right back to the start of our civilization. The ‘‘true’’ soil has been the favorite domain of the soil scientist, using ever more sophisticated methods to measure soil characteristics and to characterize dynamic soil processes. This has greatly expanded the knowledge about soils and been a major contribution to society at large as this knowledge was applied in many products and services. Effects of land use are difficult to predict in the same quantitative and unique manner in which, for example, a Cation Exchange Capacity (CEC) can be predicted because conditions are so diverse. There is no single magic answer to any given land‐use question because many stakeholders are involved with widely varying interests. The soil scientist should try to define the ‘‘true’’ soil as well as possible but should be modest and know his limits. Soil scientists have a major handicap: soils occur underground and are invisible except when excavated. Plants and animals are highly visible, at least partly explaining the viability of policies enforcing biodiversity. There are efforts now to define soil‐charters and the EU is working on soil policies.

Aspects of Jojoba Agronomy and Management

Abstract: Jojoba is a relatively new crop that is adapted to hot, dry climates. The crop is grown for its seed, which contains a wax with a high melting point. This wax is used in a variety of products, including lubricants, pharmaceuticals, and cosmetics. Various aspects of the crop agronomy and management are reviewed, including a botanical description, propagation from seed and cuttings, the genetics of the plant and wax production, and the various physical characteristics that affect the crop's growth and yield, such as soil, water, fertilizer requirements, salt, pH, temperature tolerance, and mycorrhizal status of the crop. Last, the pests (insects, arthropods, and diseases) of jojoba are reviewed. This chapter is intended to provide scientists and managers with a reference on the agronomy and management of jojoba.

Methodologies and the Practical Aspects of the Bulk Soil EC (σa)—Soil Solution EC (σw) Relations

Abstract: The total concentration of ions present in a solution is a useful indicator for salinity in fields like hydrology, environment, industry, and agriculture. Salinity evaluation in agricultural activity may be connected to research and application processes: osmotic pressure, leaching, water bodies mixing, irrigation management, water pricing, and water allocation. An immediate and simple means for salinity level evaluation is the measurement of the soil (or any other porous media) electrical conductivity (σ a ). Until the TDR‐era, σ a and soil volumetric water content (θ) were measured by two separate techniques and inevitably not in the very same spot. The introduction of TDR into soil science enabled the measurement of these two soil properties in exactly the same volume, with the highest accuracy. Moreover, pre‐TDR calculation models could be readopted and applied to handle the newly obtained data. This review voluntarily confines itself to the practical aspects of accurately converting σ a into σ w for different soil types, moisture levels, and solution chemical compositions. Subsequently, a short background description of pre‐TDR measurement methods and calculation techniques and the basics of TDR methodology are presented, and three procedures for σ a calculations are discussed, of which the Giese‐Tiemann stands out as the most recommended. Special attention is given to the once popular Dalton et al . (1984) model. Following are nine presented and compared protocols suggesting ways to evaluate σ w from σ a, θ, and soil properties. Light is thrown on the extent and significance of the curvilinearity of the σ a – σ w relations for σ w −1 . The conclusions sum up those field situations deserving special care along with ideas about further research needed to increase acceptance of the TDR technology for monitoring salinity by farmers. As always, we should remember with respect the contribution of the previous generations (Cremers, Sauer, Spiegler, Laudelout), whose deep theoretical understanding and originality were their main tools for laying the foundations for the better‐equipped generation that followed to put their ideas into practice.

The Role of Biodiversity in Agronomy

Abstract: Publisher Summary As long as human exploitation of the land and its biotic resources was restricted to small enclaves, the surrounding expanses of relatively undisturbed natural ecosystems could remain intact, with their biodiversity preserved. But, as the extent and intensity of human exploitation of the terrestrial domain increased, along with the increase of population, natural habitats were reduced and fragmented. Entire biomes are now threatened and numerous ‘‘wild’’ species have already been eliminated. Projections indicate that biodiversity loss will continue into the future, as expressed in declines in populations of wild species and reduction in area of wild habitats. All the plants whose products are utilized by humans, either directly or indirectly, were derived originally from biological diversity; that is to say, from wild ancestors. Traditionally, agricultural breeding has been done with the close genetic relatives of the relevant organisms. Genetic diversity is often considered a resource for future crop improvement. Agriculture depends on biodiversity through pollinators, birds, insect pests, disease control, and cultivated plants, and wild relatives. Numerous species in soil are directly involved in ecosystem processes and ecological services that contribute to sustaining agriculture. Soil biodiversity is determined by multiple factors: vegetation, soil physical and chemical properties, climate, and the interactions among soil organisms. N agro-ecosystem approaches strive to integrate farming and food production units into the larger environmental domain, which recognizes and preserves the role of native fauna and flora in their natural habitats. The potential impacts of climate change and climate variability on biodiversity need to be more fully characterized, because both agricultural and natural ecosystems will thereby be affected. The formulation and implementation of biodiversity policies is a global priority. National and international policies are needed to encourage the adoption on a wide scale of the agro‐ecosystem paradigm and thus the conservation of biodiversity in food-producing systems.