Advances in Agronomy (eBook)

Donald L. Sparks (Herausgeber)

eBook Download: PDF

1994 | 1. Auflage
193 Seiten
Elsevier Science (Verlag)
978-0-08-056366-4 (ISBN)

Infos

Advances in Agronomy increased its publication frequency to three volumes per year in 1993, and will continue this trend as advances in the field dictate. Volume 53 contains four excellent reviews which cover an international spectrum of advances in the crop and soil sciences. One of the most important areas of research, sustainable agriculture, is treated
in a comprehensive article in crop rotation in the twenty-first century. Aluminum in acid soils and the factors controlling its behavior are detailed in a second article. A third long review explains the role of nutrient management on water quality, which is now a critical issue for environmental conservation. The final chapter is a definitive treatise on interparticle force effects on physical behavior of soils, which has crucial influences on plant growth and yield.

Key Features
* Sustainable agriculture
* Acid soils
* Water quality and conservation
* Soil physics

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Advances in Agronomy increased its publication frequency to three volumes per year in 1993, and will continue this trend as advances in the field dictate. Volume 53 contains four excellent reviews which cover an international spectrum of advances in the crop and soil sciences. One of the most important areas of research, sustainable agriculture, is treatedin a comprehensive article in crop rotation in the twenty-first century. Aluminum in acid soils and the factors controlling its behavior are detailed in a second article. A third long review explains the role of nutrient management on water quality, which is now a critical issue for environmental conservation. The final chapter is a definitive treatise on interparticle force effects on physical behavior of soils, which has crucial influences on plant growth and yield. - Sustainable agriculture- Acid soils- Water quality and conservation- Soil physics

Inhalt

Front Cover 1
Advances in Agronomy, Volume 53 4
Copyright Page 5
Contents 6
Contributors 8
Preface 10
Chapter 1. Crop Rotations for The 21st Century 12
I. Origin of Crop Rotations 13
II. 20th Century Crop Rotations 16
III. Agronomic Impacts of Crop Rotation 22
IV. Soil Quality Effects 33
V. Biological Diversity 41
VI. Economics of Crop Rotation 43
VII. Policy Impacts on Crop Rotations 44
VIII. Summary and Conclusions 47
References 48
Chapter 2. Role of Dissolution and Precipitaion of Minerals in Controlling Soluble Aluminum in Acidic Soils 58
I. Introduction 58
II. A Framework for Understanding Mineral Dissolution and Precipitation in Soils 61
III. Factors Affecting Dissolution and Precipitation of Aluminum- Containing Minerals 62
IV. Modeling Soluble Aluminum 75
V. Aluminum in Acidic Soils: Principles and Practicalities 88
References 91
Chapter 3. Managing Plant Nutrients for Optimum Water Use Efficiency and Water Conservation 96
I. Introduction 96
II. Conserving Water Supply by Optimizing Water Use Efficiency 97
III. Conserving Water Quality through Nutrient Management 103
IV. Needs for Further Research 119
References 120
Chapter 4. Interparticle Forces: A Basis for the Interpretation of Soil Physical Behavior 132
I. Introduction 133
II. Interparticle Forces 135
III. Soil Water Relations: Swelling and Shrinkage 154
IV. Swelling of Sodium Clays 157
V. Swelling of Calcium Clays 163
VI. Surface Area and Pore Size 172
VII. Water Stability of Soil Aggregates 177
VIII. Sodic Soils and the Threshold Concentration Concept 180
IX. Concluding Remarks 187
References 188
Index 196

Textauszug

Role of Dissolution and Precipitation of Minerals in Controlling Soluble Aluminum in Acidic Soils

G.S.P. Ritchie    Department of Soil Science and Plant Nutrition, School of Agriculture, The University of Western Australia, Nedlands, Western Australia 6009, Australia

I INTRODUCTION

Acidic soils are a worldwide phenomenon that may be natural or anthropogenic in origin. Acidic precipitation and farm management practices that disrupt the carbon, nitrogen, and sulfur cycles have apparently resulted in contemporary acidification rates that are much higher than rates estimated to occur in their absence (Binkley et al., 1989; Robson, 1989). Agricultural production on acidic soils may be severely limited by a number of nutritional (e.g., nitrogen or molybdenum deficiencies) or toxicity (e.g., aluminum or manganese) problems (Robson, 1989). Aluminum (Al) toxicity, however, is considered to be the most common cause of decreased plant growth in acidic soils.

The quantity of toxic Al in acidic soils has apparently defied prediction by chemical principles because the dynamic and diverse nature of soils distinguishes reality from ideality. The ultimate aim of soil scientists is to be able to predict Al speciation (solid and solution) in time and space and then deduce the quantity of Al that is toxic to plants.

There are several different forms of Al in soils (Adams, 1984; Ritchie, 1989; Sposito, 1989a) which can all contribute to the toxic quantity of Al in solution either directly or indirectly. Al-containing minerals are the ultimate source of Al in most soils whereas organically bound, exchangeable, interlayer, and soluble, complexed Al are sinks for Al3 + released during mineral dissolution. The sinks provide Al3 + to the soil solution in the short term and hence, separately or collectively, may be seen as controlling the amount of Al3 + in solution. In the long term, even though Al may be derived from mineral compounds, the quantity released cannot necessarily be predicted from equilibrium thermodynamics because morphological characteristics may result in the surface-free energy of the mechanism of structural breakdown being greater than the standard free energy of the reaction. When this occurs, kinetic considerations become more important than thermodynamics in controlling solution quantities of Al3 + (Morse and Casey, 1988).

Lewis and Randall (1923) pointed out that “thermodynamics shows us whether a certain reaction may proceed and what maximum yield may be obtained, but gives no information as to the time required.” Hence our deductions about the processes controlling the dissolution and precipitation of Al will always be at the mercy of the time scale of our observations.

The processes and mechanisms of dissolution and precipitation have been under consideration by soil scientists and mineralogists for many years. In the context of Al solubility, an understanding of dissolution mechanisms and kinetics helps us see the limitations of trying to apply equilibrium thermodynamics to predicting activities in soil solutions and to decide on the most appropriate course of action for our needs.

The quantity of Al in the soil solution is dynamic in time and space and the measurements we make represent one moment in the time and space of a pathway. Soluble Al due to mineral dissolution and precipitation is the net result of the balance between thermodynamic and kinetic considerations, as affected by surface morphology, the uptake and release of nutrients and toxic ions by plants, and as affected by the composition and flow of water through the volume of soil being studied. When a mineral dissolves, whether it is a grain of feldspar in a granitic rock or kaolinite in a soil that is rewetting at the beginning of the wet season, the sequence of events that follows cannot be predicted by equilibrium thermodynamics alone. A process or sequence of events begins which can be described in terms of a pathway. The pathway is controlled by thermodynamics, kinetics, and surface morphology, which answer the questions: (1) what is it and where can it go? (thermodynamics), (2) how quickly will it get there? (kinetics), and (3) what does it look like? (surface morphology). For soil scientists and others working in the field, there is a fourth question: how do I know when it's there?

Many mechanisms have been put forward to describe dissolution but few have addressed all three scientific components influencing the process. Early work assumed the pathway was simply controlled by equilibrium thermodynamics (Garrels and Christ, 1965; Lindsay, 1979) but the inability of the theories to describe bulk solution concentrations led workers to postulate on nonequilibrium thermodynamics or on the physical structure of the dissolving surface and how they could lead to deviations from theoretical predictions based on the assumption of equilibrium (Helgeson, 1968; Hemingway, 1982; Hochella, 1990). In addition, the role of kinetics was also recognized to be so important (Morse and Casey, 1988) in some cases that it overshadows predictions from thermodynamic considerations.

All the theories and mechanisms that have been suggested to explain dissolution have one aspect in common: they cannot be proved unequivocally. Hypotheses that explain behavior in terms of surface morphology require experimental evidence on the molecular scale (Sposito, 1986). Until now most of the evidence has come from bulk solution measurements or spectroscopic analyses that are limited in their ability to distinguish between the surface and the interior of a mineral. However, recent advances in spectroscopic and microscopic techniques are providing methods that can study the hydrated surface layers of a dissolving grain (Hochella, 1990; Brown, 1990; Mogk, 1990).

This review considers the role of mineral dissolution and precipitation in controlling solution quantities of Al and our attempts to predict the outcome of these processes. Its purpose is to broaden our perspective and thereby increase our ability to predict (Al3 +) accurately by providing soil scientists with possibilities for looking at the problem from a different perspective by drawing on examples from related disciplines such as geochemistry. The dissolution and precipitation of Al-containing minerals are by no means the only mechanisms controlling Al3 + in soil solutions (Ritchie, 1994). It is an area, however, that requires more clarity so that its contribution to the overall scheme of events can be appreciated more appropriately. The new perspectives may then enable us to predict more accurately the variation in solution composition with time and space of acidic or acidifying soils, before and after amelioration. Within this framework, the chemical paradigms that have been mistaken for principles and the paradigms of mineral and solution phases that exist in our soils in apparent defiance of chemical principles will be discussed.

II A FRAMEWORK FOR UNDERSTANDING MINERAL DISSOLUTION AND PRECIPITATION IN SOILS

In a closed system, the amount and composition of a mineral that dissolves or precipitates may be described in terms of chemical thermodynamics and kinetics as affected by the surface morphologies of the dissolving and precipitating species (Fig. 1). It is not possible to understand fully the processes and pathways of precipitation and dissolution without considering the interactions among thermodynamics, kinetics, and surface morphology.

Figure 1 The three components influencing dissolution and precipitation.

Chemical thermodynamics describes the pathway and predicts mineral and solution speciation from the standard free energy change of a chemical reaction (∆G°r) and the composition of the soil solution and the minerals present. Such considerations may assume that equilibrium can be achieved [i.e., the free energy (G) of the system reaches a minimum]; that non- or quasi-equilibrium exists [i.e., metastable products (e.g., smectites, Al-substituted goethite, and hematite) persist on a time scale considered long for soils]; or that an irreversible reaction occurs (i.e., a rock component dissolves completely).

Even though the driving force for precipitation or dissolution may be great from a thermodynamic standpoint (i.e., a lot of free energy, ∆G, can be lost), the thermodynamic potential for a mineral to form or dissolve [(1) in Fig. 1] may be overshadowed by kinetic considerations. The rate of precipitation or dissolution may be very small because the driving force (i.e., change in energy) is small. Thermodynamics indicates which reactions are possible whereas kinetics stipulate the time required for transformations and hence can frequently mediate the pathway of a reaction [(2) in Fig. 1]. Kinetic considerations include transport of ions in solution, reaction rates in solution, and rates of nucleation, crystal growth, and dissolution.

The energy changes described by chemical thermodynamics and kinetics during dissolution and precipitation may be modified by the surface morphology of the mineral (i.e., composition, structure, topography, thickness, and surface area). The surface morphology is the physical manifestation of the processes and rates of dissolution and precipitation. The soluble components predicted by thermodynamics can influence all the aspects of surface morphology [(3) in...

Produkt-Details

• Erscheint lt. Verlag: 7.11.1994
• Sprache: englisch
• Themenwelt: Sachbuch/Ratgeber
• Themenwelt: Naturwissenschaften ► Biologie ► Ökologie / Naturschutz
• Themenwelt: Naturwissenschaften ► Chemie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Mineralogie / Paläontologie
• Themenwelt: Technik
• Themenwelt: Weitere Fachgebiete ► Land- / Forstwirtschaft / Fischerei
• ISBN-10: 0-08-056366-X / 008056366X
• ISBN-13: 978-0-08-056366-4 / 9780080563664