Productivity and management of rice–wheat cropping systems: issues and challenges

Lowland river–floodplain systems are characterized by a high degree of variability in both the frequency and period of inundation of various parts of the floodplain. Such variation should profoundly affect the processes underlying nutrient transformations in these systems. This paper explores the effect of various hydrologic regimes on nutrient cycles. Partial drying of wet (previously inundated) sediments will result in an increased sediment affinity for phosphorus and will produce a zone for nitrification coupled with denitrification. Hence, partial drying may reduce the availability of nitrogen (N) and phosphorus (P). Conversely, complete desiccation of sediments may lead to the death of bacteria (and subsequent mineralization of N and P), a decrease in the affinity of P for iron minerals, a decrease in microbial activity and a cessation of all anaerobic bacterial processes (e.g. denitrification). Colonization of exposed sediments by terrestrial plants may lead to N and P moving from the sediments to plant biomass. Re-wetting of desiccated soils and sediments will result in an initial flush of available N and P (which can be incorporated into bacterial or macrophyte biomass), coupled with an increase in bacterial activity, particularly nitrification. Inundation of floodplain soils will result in the liberation of C, N and P from leaf litter and floodplain soils. This will result in an increase in productivity, which ultimately may lead to the onset of anoxia in floodplain soils and, consequently, an increase in anoxic bacterial processes such as P release and denitrification. Copyright © 2000 John Wiley & Sons, Ltd.

The effects of drying and re-flooding on the sediment and soil nutrient dynamics of lowland river-floodplain systems: A synthesis

Phosphorus (P) is essential for plants and animals because of its role in vital life processes, such as in photosynthesis in plants and energy transformations in all forms of life. It also has a significant role in sustaining and building up soil fertility, particularly under intensive systems of agriculture.

Chemistry of Phosphorus Transformations in Soil

Preface.Acknowledgements.1. Introduction.1.1 Global Extent of Submerged Soils and Wetlands.1.2 Biogeochemical Characteristics.1.3 Types of Submerged Soil.1.3.1 Organic Soils.1.3.2 Mineral Soils.1.3.3 Relation between Soils and Landform.2. Transport Processes in Submerged Soils.2.1 Mass Flow.2.2 Diffusion.2.2.1 Diffusion Coefficients in Soil.2.2.2 Propagation of pH Changes Through Soil.2.3 Ebullition.2.4 Mixing by Soil Animals.3. Interchange of Solutes between Solid, Liquid and Gas Phases.A. WATER.3.1 Composition of the Water.3.1.1 Acid and Bases.3.1.2 Speciation.3.1.3 Equilibrium Calculations.3.2 pH Buffer Capacity.3.3 Equilibrium with the Gas Phase.3.3.1 Floodwater CO2 Dynamics.3.4 Gas Transport Across the Air-Water Interface.3.4.1 CO2 Transfer Across the Air-Water Interface.B. SOIL.3.5 The Solid Surfaces in Soils.3.6 The Solid Surfaces in Submerged Soils.3.6.1 Organic Matter in Submerged Soils.3.7 Solid-Solution Interactions.3.7.1 Adsorption.3.7.2 Precipitation.3.7.3 Co-Precipitation in Solid Solutions.3.7.4 Inhibition of Precipitation.3.7.5 Equations for Solid-Solution Interactions.4. Reduction and Oxidation.4.1 Thermodynamics and Kinetics of Redox Reactions.4.1.1 Electron Activities and Free Energy Changes.4.1.2 Redox Potentials.4.1.3 Relation between pe and Concentration of Redox Couples.4.1.4 pe-pH Diagrams.4.1.5 Energetics of Reactions Mediated by Microbes.4.2 Redox Conditions in Soils.4.2.1 Changes with Depth in the Soil.4.2.2 Changes with Time.4.2.3 Calculated Changes in pe, pH and Fe During Soil Reduction.4.2.4 Measurement of Redox Potential in Soil.4.3 Transformations of Nutrient Elements Accompanying Changes in Redox.4.3.1 Transformations of Carbon.4.3.2 Transformations of Nitrogen.4.3.3 Transformations of Sulfur.4.3.4 Transformations of Phosphorus.4.4 Oxidation of Reduced Soil.4.4.1 Kinetics of Fe2+ Oxidation.4.4.2 Simultaneous Diffusion and Oxidation in Soil.5. Biological Processes in the Soil and Floodwater.5.1 Microbiological Processes.5.1.1 Processes Involved in Sequential Reduction.5.1.2 Nitrate Reduction.5.1.3 Iron and Manganese Reduction.5.1.4 Sulfate Reduction.5.1.5 Methanogenesis.5.1.6 Aerobic Processes.5.2 Macrobiological Processes.5.2.1 Net Primary Production and Decomposition.5.2.2 The Floodwater-Soil System.5.2.3 Floodwater Properties.5.2.4 Floodwater Flora.5.2.5 Fauna.5.3 Is Biodiversity Important?6. Processes in Roots and the Rhizosphere.6.1 Effects of Anoxia and Anaerobicity on Plant Roots.6.1.1 Adaptations to Anoxia.6.1.2 Armstrong and Beckett's Model of Root Aeration.6.2 Architecture of Wetland Plant Root Systems.6.2.1 Model of Root Aeration versus Nutrient Absorption.6.2.2 Root Surface Required for Nutrient Absorption.6.3 Nutrient Absorption Properties of Wetland Plant Roots.6.3.1 Ion Transport in Roots.6.3.2 Ion Transport in Wetland Roots.6.4 Root-Induced Changes in the Soil.6.4.1 Oxygenation of the Rhizosphere.6.4.2 The pH Profile Across the Rhizosphere.6.5 Consequences of Root-induced Changes.6.5.1 Nitrification-Denitrification in the Rhizosphere.6.5.2 Solubilization of Phosphate.6.5.3 Solubilization of Zinc.6.5.4 Immobilization of Cations.6.6 Conclusions.7. Nutrients, Toxins and Pollutants.7.1 Nutrient and Acidity Balances.7.1.1 Nutrient Balances in Ricefields.7.1.2 Acidity Balances in Ricefields.7.1.3 Peat Bogs.7.1.4 Riparian Wetlands.7.1.5 Tidal Wetlands.7.2 Toxins.7.2.1 Acidity.7.2.2 Iron Toxicity.7.2.3 Organic Acids.7.2.4 Salinity.7.3 Trace Elements.7.3.1 Global Cycling of Trace Elements.7.3.2 Transport Through Soil and into Plant Roots.7.3.1 Mobilities of Individual Trace Elements.8. Trace Gases.8.1 Methane.8.1.1 Global Budget.8.1.2 Processes Governing Methane Emissions from Rice.8.1.3 Modelling Methane Emission.8.1.4 Estimating Emissions at the Regional Scale.8.1.5 Possibilities For Decreasing Emissions.8.2 Nitrogen Oxides.8.2.1 Global Budget.8.2.2 Processes Governing Nitrous and Nitric Oxide Emissions from Rice.8.2.3 Differences between Rice Production Systems.8.3 Ammonia.8.3.1 Global Budget.8.3.2 Processes Governing Ammonia Emissions from Rice.8.4 Sulfur Compounds.8.4.1 Global Budget.8.4.2 Emissions from Ricefields.8.5 Carbon Sequestration.References.Index.

http://base.dnsgb.com.ua/files/book/Agriculture/Soil/The-Biogeochemistry-of-Submerged-Soils.pdf

D. S. Mikkelsen

Papers

Phosphorus Behavior in Flooded-Drained Soils. II. Iron Transformation and Phosphorus Sorption

Phosphorus Behavior in Flooded-Drained Soils. III. Phosphorus Desorption and Availability