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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.

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 chemistryWe 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.

Most agriculture is practiced under rainfed conditions with varying supplies of water. Farming strategies and tactics divide roughly into those dealing with too much water and those for coping with too little. A discussion of the large diversity of methods that has been developed for rainfed conditions reveals critical relations between production and water supply. We begin with comments on the management of farming in wet regions where hazards and management practices to counter them are rather different from those in dry regions. Chapter 14 examines the principles of irrigation as a separate topic.Agriculture in wet regionsRainfed agriculture in humid regions would seem blessed with a free good in its generous water supply. But that supply is seldom ideal, varying from excess to transient deficiency. Excess supply leading to surface flooding and saturated soils is a major problem that generally requires drainage works (Section 12.6) but new biological solutions are being found to some problems. A successful example of combating flooding damage of rice, a major problem in many areas of southeast Asia, is presented in Box 13.1. Water erosion (Section 12.7) and nutrient loss are also greater concerns with abundant rainfall than in drier regions. Leaching of N was considered in Section 8.4.3. Because vegetative cover serves to control erosion and nutrient losses, many sloping sites are maintained in pasture. Many low lying sites also remain in pasture because cold, wet soil and poor drainage combine to make them unsuited to cropping.

Wheat has been grown in Australia since European settlement, initially to feed colonists, but soon as an export crop. Although total national production, 19 Mt (five-year average 2003–2008), remains small by world standards, the high proportion (60%) that is exported ranks Australia fourth, after the USA, Canada, and the EU, among wheat exporting countries.This chapter describes the continuing evolution of wheat-cropping systems in semi-arid southern Australia (annual rainfall 300–500 mm) using yield data for the State of Victoria from soon after inception of the industry c. 1800. The analysis reveals how a sequence of cropping systems has developed in response to technological innovation, economic incentives, and societal pressures. Economic pressure to compete on world markets has been, and will likely remain, a major driver of change in these cropping systems. Producers receive little subsidy to relieve competitive pressure. Among OECD countries, subsidies account for 25 and 40% of farm income in the USA and the EU, respectively, but only 6% in Australia. Driving forces for change may be further complicated by widely anticipated climate change.Producers, agronomists, and researchers now have access to new tools to meet the increasingly complex objectives that must account for variability in climatic and economic environments, and also address societal interests. The principles and range of strategies and tactics available to combat crop response to low and variable rainfall have been presented in Chapters 9 and 13.

Electromagnetic radiation is a central feature of crop environments; its energy determines soil and air temperatures, wind movements, evaporation, and photosynthesis. This chapter examines radiation sources and their roles in the macro- and microclimates of crops. When objects absorb radiation their temperature increases. That heat energy may remain in the object or it may be radiated as new long-wave radiation, transferred to another object, or dissipated in evaporation of water. All of these subjects are covered here. We begin with a review of several physical laws important in radiative transfers of energy among plants, soil, and atmosphere, as well as from the Sun.Radiation conceptsTwo types of electromagnetic radiation, distinguished by their sources and spectral distributions, are important in crop environments. Solar radiation from a very hot thermal radiator, the Sun, is termed short-wave radiation (SW) because most energy is received in relatively short wavelengths, 0.3 to 3 μm. In contrast, thermal radiation from objects on our planet, including soils, plants, and atmosphere occurs at longer wavelengths because these radiating bodies are at much lower temperatures. Such long-wave radiation (LW) is found mainly between 5 and 100 μm.Thermal radiationAll objects with a temperature greater than 0 K are sources of a continuous spectrum of electromagnetic radiation that, because of its source, is termed thermal radiation. Intensity and spectral distribution of thermal radiation may be compared with those from a reference “black body”.

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.

While the future is uncertain in terms of population, demand for food, energy supply, climate and weather, it is worthwhile to consider some scenarios, based on expected trends, from a crop ecology perspective. Critical to this exercise is whether agricultural production can be increased to meet food and fuel needs of an expanding population and whether that can be done safely with acceptable environmental impact. Success in achieving a sufficient agriculture will depend heavily on the rate of population growth, expected demand of individuals, and on decisions made about acceptable levels of natural resource conservation and energy use. Preceding chapters provide a basis for possible technological advances. This chapter reviews trends in population growth and food supply and considers the prospects for a food-secure world to 2050.Population and need for foodWorld population of 6.8 billion in 2010 is continuing to grow but at a decreasing rate, recently predicted (in 2008) by the UN Population Division to reach 9.2 billion by 2050, and later decline toward the end of the century. The decline is good long-term news regarding overall food demand and environmental impact. But it also includes a crucial 40-year period when greater food production must be achieved in the face of demographic shifts that will have great impact on future agriculture. In fact, the time available for development of the required science and technology is much shorter than 40 y because it takes time for validation, adaptation, extension education, and adoption on farms.

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.

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 energyEarth 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.

Assimilates from photosynthesis serve as substrates for respiration and growth. Sucrose is the principal transport form in crop plants and sucrose and starch are the main storage forms. Assimilates are consumed in respiration providing energy to maintain cellular processes and also for biosynthesis of new materials. It is the partition of those materials, also originating from the same pool of assimilates, that changes the size and morphology of plants during a growing season. This is evident in the changing numbers of stems, leaves, and reproductive structures and its control is an objective of crop production. Here we begin the discussion of partitioning with assimilate use in respiration and biosynthesis.Carbon use in respiration and synthesisRespiration furnishes energy for new construction and for maintenance of existing structures. The portion linked with growth is termed growth respiration, Rg. The magnitude of Rg varies with the chemical nature of newly constructed biomass. Maintenance respiration, Rm, also depends on tissue composition and has precedence over growth for assimilate; together Rm and Rg ordinarily consume 30 to 50% of gross photosynthesis. Respiration and chemical composition of new biomass, then, are important aspects of carbon partitioning.The respiratory processRespiration occurs in the mitochondria of all living cells and is termed “mitochondrial” or “dark” respiration, thus avoiding confusion with photorespiration (Section 10.1.2). Carbon enters mitochondria as organic acids derived in the cytosol from protein, carbohydrate, or lipid. Within mitochrondria, the tricarboxylic acid (TCA) cycle and electron transport chain accomplish the chemical transformations.