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Index
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- Crop Ecology
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- 28 April 2011, pp 546-556
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References
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- 28 April 2011, pp 516-545
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17 - Technological change in high-yield crop agriculture
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- Crop Ecology
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- 28 April 2011, pp 458-483
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Summary
In the last half century, Earth's population has increased two-fold while land used to produce food, livestock feed, and fiber crops rose by only 13%. This considerable achievement has been called a green revolution made possible by a powerful combination of new technologies, including genetic improvement of major staple food crops, development and widespread use of mineral fertilizers and pesticides, and expansion of irrigated area. The result is that a few high-yield cropping systems now provide the major portion of human food from a relatively small area of arable land (Chapter 1.2). While these developments have had remarkable success in raising productivity and sparing natural ecosystems from conversion to agriculture, there are nonetheless growing concerns about negative environmental impacts. Here we learn how rapid technological advancement enabled conversion to high-yield systems and consider future challenges to sustaining them and their high productivity.
Common features of high-yield systems
High-yield cropping systems have evolved through intensification of traditional systems during the past 50 years. This process involved: (i) producing more crops per year per unit land area, i.e., temporal intensification; and (ii) more intensive use of inputs (fertilizers, manure, irrigation, pesticides) to alleviate yield-limiting abiotic and biotic stresses, i.e., input intensification. High-yield systems are not only found in developed countries where large-scale, mechanized agriculture predominates, but also in developing countries where small-scale, labor-intensive systems remain the norm. Examples of the latter include continuous rice, rice–wheat, and cotton and sugarcane systems in developing countries of south, southeast, and east Asia.
Part V - Farming past, present, and future
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- Crop Ecology
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- 28 April 2011, pp 437-438
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Summary
In the first edition of this book, published in 1992, we presented two case studies of important farming systems, wheat–sheep farming in southern Australia and maize–beef production in central USA, discussing how they operated based on current knowledge, technology, and economic conditions. The purpose was to integrate the knowledge and principles presented in earlier chapters and show how success in farming depends upon this integration. Economic survival required a sustainable system, which could be analyzed in terms of balances of water, nutrients, and capital. In addition, farmers had to be nimble in adapting to variable climatic and economic environments. We also hoped that those analyses would serve to encourage readers to make detailed analyses of other farming systems. Those examples remain available to readers on the internet and can continue to meet those goals. However, and unsurprisingly, these analyses are substantially out of date with regard to current cropping systems in those regions. Knowledge and technology have advanced rapidly, global population and demand for agricultural products have increased substantially, and economic conditions have changed dramatically.
In this edition we wish to emphasize that dynamic nature of agricultural and farming systems and stress how developments in technology have and will continue to provide farmers with the capacity to remain economically viable over the short term, and sustainable over the longer term. For this we present two new chapters. Chapter 16 examines the development of wheat production systems in southern Australia since inception of the industry in 1850.
4 - Genetic resources
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Crop plants carry information acquired during their evolution and breeding that determines their performance in agricultural fields. That information is held in the genetic material of living plants and is subject to change through mutation and through recombination into new patterns, and can be lost. Proper management of this resource involves knowing the capabilities of germplasms, maintaining and improving their genetic constitution, and employing them advantageously in farming.
The terminology relating to genetic resources is in a state of flux. Here we use germplasm to denote the totality of genes and genetic combinations found in a species, or a major portion of it. A genetic population (sometimes “line” or “strain”) describes a smaller group of individuals (plants or seed) that share common ancestry and genes, and thus common traits. This use of the term population differs from that of population ecologists, who use it to denote closely related individuals that cohabit in time and space.
Genetic diversity in agriculture
Genetic diversity in farming can be defined at several levels. Here we deal with diversity of species and cultivars.
Species diversity
Thousands of plant species have been cultivated at some time or place, and several hundred are currently employed as crops, yet most crop production is derived from only a small number. Data presented in Table 4.1 account for most global production from arable land and permanent crops.
1 - Agricultural systems
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Humans depend on agriculture to provide food, feed, fiber, and fuel. Production of these organic materials in individual fields depends upon the physiological abilities of plants and the soil and aerial environments in which they grow. What crops are grown, and how, are human decisions that depend upon usefulness and value of products, costs of production, and risks involved. At the farm level, those considerations are rationalized with need for animal feeds, availability of labor, and requirements for crop rotation to raise fertility and control disease, weeds, or erosion. Additional constraints are imposed by market forces and availability of capital and technology.
Within these socioeconomic considerations, crop response to environment and management follows the laws of thermodyamics and conservation of energy and mass. Therefore, we can understand and predict crop performance using ecological analyses in terms of biological, chemical, and physical principles. This is the context and content of crop ecology.
In this chapter, we introduce ideas about the nature, objectives, and management of farming to provide a foundation for detailed analyses of crop performance in agricultural systems. We also present the guiding principles upon which this book is constructed.
On the nature of agriculture
Agriculture can be studied at various organizational and geospatial levels, from individual fields, to their grouping in farms, and to grouping of farms within regions. This is illustrated in Fig. 1.1 and identifies the need to establish a coherent terminology.
3 - Community concepts
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Crop communities can be described in simple terms. Species and cultivar define genetic content while density, spacing pattern, plant size, and stage of development define structure. The type of community is termed a monoculture when only one crop species is grown in a field at a time; the terms polyculture and mixed cropping apply to communities with two or more cohabiting crop species. Other definitions and terms exist but these are the traditional ones employed by agronomists. Most arable farming involves rotations of monocultures over time whereas pastures are mostly polycultures.
Critical issues in crop ecology, which we will examine in detail in this chapter, include the impact of community structure on resource capture and yield of crop production systems and interactions between component plants.
Community change
Concepts of community structure evolved from complementary work by agronomists who study managed communities and by botanists concerned with natural communities. In agriculture, small differences in production are important and agronomists study how production rate, competition, limiting factors, and genetic expression influence behavior of simple communities. Botanists, faced with highly diverse, natural systems give greater attention to community species composition in relation to adaptive traits and evolution. A background in plant ecology is useful for agriculturalists, and vice versa. Natural communities are subject to continuing change as different species of plants invade a site and displace earlier occupants. This process is termed succession and the sequence followed, the sere.
Contents
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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2 - Trophic chains
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Plants provide all energy for maintenance, growth, reproduction, and locomotion of every living organism on our planet. That energy, originating from the Sun, flows from plants through a web of herbivores, carnivores, and decomposers. This trophic chain – “who eats whom” – gradually returns carrier CO2 molecules to the atmosphere. Fires, occurring naturally from lightening strikes, or provoked by human activities, are a more sudden, but chemically similar, release of solar energy accumulated by plants.
Humans and some other animals also use plant material (biomass) for construction but humans alone have combusted them under controlled conditions to provide heat for warmth, cooking, and both stationary power and traction. Once, animals were the only source of traction and, in the eighteenth century, consumed as much as one third of agricultural production. Biomass accumulated by plants during previous geological periods formed coal and oil (fossil fuels) that have driven the development of transportation, agriculture, and industry during recent centuries.
Agricultural systems have developed predominantly to provide food for humans in plant and animal products, but they also provide fiber and fuel. This chapter describes the chemical and energetic content of plant products and explains their relationship to nutritive value and carrying capacity of land for animals used in agriculture and for humans. Questions of energy use in agriculture and its potential to supply a greater proportion of society's demand for non-dietary energy, including the current focus on biofuel, are discussed further in Chapter 15.
Crop Ecology
- Productivity and Management in Agricultural Systems
- 2nd edition
- David J. Connor, Robert S. Loomis, Kenneth G. Cassman
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Food security and environmental conservation are two of the greatest challenges facing the world today. It is predicted that food production must increase by at least 70% before 2050 to support continued population growth, though the size of the world's agricultural area will remain essentially unchanged. This updated and thoroughly revised second edition provides in-depth coverage of the impact of environmental conditions and management on crops, resource requirements for productivity and effects on soil resources. The approach is explanatory and integrative, with a firm basis in environmental physics, soils, physiology and morphology. System concepts are explored in detail throughout the book, giving emphasis to quantitative approaches, management strategies and tactics employed by farmers, and associated environmental issues. Drawing on key examples and highlighting the role of science, technology and economic conditions in determining management strategies, this book is suitable for agriculturalists, ecologists and environmental scientists.
Conversions and constants useful in crop ecology
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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15 - Energy and labor
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
All human activity requires energy. The inescapable minimum is dietary energy to maintain the population. In earlier times, if each hunter-gatherer could collect around 33 MJ every day for a family unit (man, woman, and two children), then survival was possible. In practice, additional organic materials, mostly non-dietary, were needed for shelter, clothing, and combustion (cooking and warmth).
Agriculture provided a way to secure that supply, and more, with less environmental hazard and less competition from other organisms. The development and maintenance of industrialized cultures is based upon the substitution of energy for labor in mandatory activities of food provision. By success in raising and stabilizing yields, agriculture has supported an increasing population and released an increasing proportion from labor in food production. Greater participation in cultural, leisure, recreational, and scientific activities improves well-being for all and advances human civilization.
The purpose of this chapter is to explain the extent, pattern, and significance of energy use in agriculture so that we might understand how agriculture at various stages of development can respond to changes in the supply and cost of energy and labor.
Sources and utilization of energy
Earth systems capture energy that originates on Earth and beyond. Earth energy comprises a small geothermal heat flux and the essentially “limitless” nuclear energy of matter. Energy captured from outside is dominantly the flux of radiant energy originating in nuclear fusion reactions in the Sun (Section 6.1), and supported by kinetic energy in ocean currents and tides caused by gravitational forces of planetary motion.
Preface
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- 28 April 2011, pp xi-xii
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Summary
Humans make extensive use of land, water, energy, labor, and other resources in the production of crops and pastures. We do this because it is essential to our survival and well-being. As world population grows, so does demand for continuing success in agriculture. And as more land is used in agriculture, concerns for loss of natural ecosystems and biodiversity increase as well. The conflict between production and conservation can only be resolved with cropping systems that are highly productive, efficient, and sustainable.
Agricultural management involves plant communities and areas of land. It requires knowledge of individual plant behavior under crowded conditions and interactions of plant communities with aerial and soil environments. These organismal and higher levels of biological organization are the subjects of ecology at different spatial scales, but explanation of these behaviors depends upon integration of relevant knowledge spanning lower levels from molecules and cells to organs. Ecology can thus be characterized as an integration of other disciplines. In turn, however, it provides specialist disciplines with context and relevance and, further, explains that in isolation they rarely affect system outcome. Crop ecology has additional dimensions in agricultural technology that interface with engineering, information and social sciences, and perspectives provided through history.
7 - Soil resources
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Soils are formed in situ over long periods under the influences of climate and vegetation during which they develop characteristic vertical profiles. Inorganic materials are the major component of soils. These include partially weathered parent materials, secondary minerals, and dissolved salts. Other components are air, water, organic matter in various stages of decay (with the most reduced form called humus), and living organisms including plant roots. Typical agricultural soils have a bulk density (dry mass per unit volume) near 1.3 g cm−3 [1300 kg m−3 or 13 × 106 kg (m depth)−1 ha−1]. Organic matter ranges by mass from 1 to 5% in mineral soils, and can be 80% or more in peaty soils. In typical mineral soils, water content at drained capacity accounts for 0.1 to 0.4 times the soil volume but some organic and volcanic soils hold much more. Understanding the physical, chemical, and biological properties of soils as media for plant growth provides insight into plant adaptations to soil conditions and crop management practices to overcome soil-related constraints.
Soil chemistry
We begin with a review of several concepts important to the study of soils and crops. Familiarity with these concepts is fundamental to crop ecology. Soil composition is dominated by an abundance of insoluble compounds of aluminum, silicon, and calcium, and soil chemistry centers on interactions between those solids and the water phase, called the soil solution.
Frontmatter
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Species list
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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12 - Soil management
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Interactions among soil properties, soil processes, and management outcomes are the subject of this chapter. Soil properties constrain, through supplies of water and nutrients, the type of farming that may be practiced. In turn, soils are altered by farming in ways that affect their long-term value for agriculture. As a result, proper management of soil resources is the key to sustaining agriculture. Here we consider how management affects soil characteristics important for short-term productivity and longer term sustainability with a focus on ability to supply essential plant nutrients and water, and ease of tillage.
Spatial variability
Soil management aims at creating favorable and reasonably uniform conditions for plant growth in all parts of individual fields. Spatial variability of landscapes limits attainment of these goals, and soil profiles are seldom uniform. For optimum management, places with different textures, profile depths, slopes, drainage, and native fertility would be farmed differently. Although potential for within-field variation in soil properties increases with field size, small fields introduce another set of problems related to access roads, fencing, unused headlands, and excessive turning space in mechanized systems. Efficient farming requires compromises between field size and degree of heterogeneity although the tendency has been towards larger field size in mechanized cropping systems. Typical field size in the US Corn Belt, for example, is 30 to 60 ha; in Mato Grosso, Brazil, fields in soybean-based systems are often > 200 ha.
9 - Water relations
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Plants grow by fixing, in photosynthesis, CO2 that diffuses into leaves from the atmosphere through open stomatal pores in leaf surfaces. An inevitable consequence is that water vapor evaporates from wet cell walls that surround sub-stomatal cavities and diffuses through stomates to drier air outside. Water loss must be controlled or replaced if the plant is to maintain turgor and metabolic activity. Water is also a primary reactant in photosynthesis but the proportion of water required by plants that is chemically incorporated in their structure, or is used to maintain their water content as they grow, is very small.
Crops differ significantly in rooting habit and thus in their ability to acquire water from soil. Owing to differences in epidermal wax and in size, frequency, and behavior of stomates, they also vary in their ability to control loss of water from leaves. Control of water loss is always made at the expense of CO2 uptake for growth. For crops, flow of water from the soil to the atmosphere through plants is accompanied by direct evaporation of water from soil, particularly when the surface is wet and unprotected by foliage. The discussion of plant and crop water relations presented in this chapter draws heavily on the information presented in Chapter 6 (Aerial environment) and is essential background to understanding the productivity and effective management of rainfed and irrigated crops presented in Chapters 13 and 14.
10 - Photosynthesis
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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Summary
Photosynthesis is the primary process in crop production. It supplies reduced carbon for the construction of biomass and as the source of energy in metabolism. Leaves are the functional units of crop photosynthesis; their efficiency in capture and utilization of solar energy determines productivity. The transport of CO2 from the atmosphere to sites of fixation in leaves is limited by slower moving air within canopies, boundary layers of still air surrounding leaves, stomatal pores in leaf epidermis, and by the interior structure of leaves.
The area (LAI) and arrangement of foliage, i.e., canopy architecture, determine the interception of solar radiation by individual leaves of a crop. Leaf area and arrangement change during crop growth and, by leaf movement, during each day. Maximum crop production requires complete capture of solar radiation and supporting levels of water and nutrients. When water or nutrients are in short supply, productivity is reduced by incomplete capture of radiation and/or less efficient utilization of it.
This chapter begins with a discussion of photosynthesis and photosynthetic responses of leaves progressing to analyses and explanations of spatial and temporal variation of photosynthesis of crop canopies.
Photosynthetic systems
The central processes of photosynthesis are common to all plants but variants have evolved ancillary chemical, morphological, and physiological mechanisms that result in three photosynthetic systems with important ecological adaptations.
Part I - Farming systems and their biological components
- David J. Connor, University of Melbourne, Robert S. Loomis, University of California, Davis, Kenneth G. Cassman, University of Nebraska, Lincoln
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- Crop Ecology
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A view from space gives emphasis to areal dimensions of vegetation and agriculture at the thin interface between atmosphere and solid earth. It is only by spreading plants across the landscape that they can efficiently intercept fluxes of limiting resources such as CO2, water, and sunlight. Farmers make strategic and tactical decisions about planting and management to optimize rates of crop growth and accumulation of yield. In farming, land is divided into individual fields as the units of management and production. In ecological terms, plants that occupy those fields constitute a community of cohabiting organisms. A community, considered together with the chemical and physical features of the environment, forms a further fundamental grouping, the ecosystem.
Farmers' efforts in crop and pasture management aim at beneficial control over the structure of crop communities and physical and chemical aspects of their environment. These issues are introduced in Chapter 1, which also presents five major themes that recur throughout the book. Chapter 2 presents concepts of trophic chains seminal to understanding the role of animals in agriculture and the nutritional requirements of humans. Establishment and productivity of plant communities dominated by agricultural species is presented in Chapter 3, and their genetic resources in Chapter 4. This part terminates, in Chapter 5, with a discussion of plant phenological development as the primary basis for adaptability to environment and determination of reproductive yield.