08152 - Soil Chemistry

Learning outcomes

At the end of the course, students will possess a sound understanding of the fundamental principles governing soil genesis, soil composition, and the physico-chemical and biological properties of soils. They will be able to understand, at the molecular level, the mechanisms that control soil surface reactivity and, consequently, the functioning of agroecosystems.

Course contents

Prerequisites

Students are expected to have a solid background in the fundamentals of mathematics, physics, chemistry, plant biology, and soil science. These prerequisites are provided through the first-year courses of the Degree Programme. Students are strongly encouraged to complete these courses before taking the examination in Soil Chemistry.

Course contents

The course provides the fundamental chemical principles required to understand soil composition and the main physico-chemical processes governing soil behaviour in agricultural and forest systems. Starting from the definition and functions of soil, together with a concise overview of the main processes of soil genesis, the course examines the mineral, organic and fluid components of the soil system, with particular emphasis on their chemical structure, surface reactivity and mutual interactions.

The unifying theme of the course is the relationship between soil composition, soil surface reactivity, and the physico-chemical processes that regulate the functioning of agroecosystems. Particular attention is devoted to adsorption, ion exchange, soil acidity, redox processes and salinity, which govern the behaviour and mobility of chemical elements within the soil system.

This course constitutes the first module of the Integrated Course Chemistry and Biochemistry of the Agroforestry Environment and focuses on the chemical and physico-chemical aspects of the soil system, providing the knowledge required to understand soil composition, surface reactivity and the processes controlling soil behaviour. The educational pathway is completed by the module Biogeochemical Cycling in Agroforestry Systems, which is delivered through the course Agricultural Chemistry and Soil Fertility, which focuses on the biochemical transformations of soil organic matter and the dynamics of chemical elements within the soil–plant system. The two modules are designed as complementary components of a unified educational pathway aimed at understanding the functioning of agroecosystems.

UNIT 1 – THE SOIL AS A COMPLEX NATURAL SYSTEM: COMPOSITION AND PROPERTIES (20 HOURS)

1.1 Soil and its functions

Definition of soil and the main disciplinary approaches to its description. Soil as an interface between the lithosphere, atmosphere, biosphere and hydrosphere. Soil functions, ecosystem services and the concept of the Critical Zone.

1.2 Soil genesis and mineral components

Overview of the main factors and processes involved in soil genesis. Mineral weathering and soil formation. Chemical structure of minerals, basic crystallography, primary and secondary minerals, phyllosilicates, oxides and hydroxides. Physico-chemical properties of mineral colloids, including specific surface area, surface charge and the point of zero charge.

1.3 Soil organic matter

Definition and determination of soil organic matter. Biochemical composition, dynamics and transformation of soil organic matter in agricultural and forest systems. The carbon cycle, humification processes, organo-mineral associations and soil organic matter stabilization. The rhizosphere as a biological interface.

1.4 Soil fluid phases

Composition of soil air and soil solution. Ionic activity and chemical equilibria in soil solution. Dissolution, complexation and precipitation processes.

UNIT 2 – SOIL SURFACE REACTIVITY AND THE MAIN PHYSICO-CHEMICAL PROCESSES OF THE SOIL SYSTEM (20 HOURS)

2.1 Soil surface chemistry

Origin and nature of reactive soil surfaces. Surface functional groups, permanent and variable charge, point of zero charge, and the electrical double layer theory. Adsorption and desorption processes, adsorption isotherms, cation and anion adsorption, and surface precipitation.

2.2 Ion exchange processes

Cation and anion exchange capacity. Ion exchange equilibria, exchanger selectivity, and the role of ion exchange in controlling the retention and mobility of chemical elements within the soil system.

2.3 Redox processes in soils

Redox potential and oxidation-reduction reactions in soils. Eh-pH diagrams. Influence of redox conditions on the mobility and bioavailability of chemical elements. Waterlogged soils and the behaviour of potentially toxic elements.

2.4 The chemistry of acid soils

Active, exchangeable and potential acidity. Natural and anthropogenic acidification processes. Effects of soil acidification on soil properties and approaches to the management and amelioration of acid soils.

2.5 The chemistry of saline and sodic soils

Origin and causes of soil salinity and sodicity. Effects of salinity and sodicity on the chemical and physical properties of soils. Principles and approaches for the reclamation and management of saline and sodic soils.

UNIT 3 – LABORATORY SESSIONS (10 HOURS)

The laboratory sessions are designed to apply the theoretical concepts developed during the course to the experimental determination of the main chemical properties of soils. Practical activities will include:

• extraction of soil organic matter and separation of humic substances;
• determination of cation exchange capacity (CEC);
• determination of soil pH;
• determination of soil salinity;
• interpretation of the main soil chemical analyses.

Particular emphasis will be placed on the interpretation of analytical data, the correct use of physical quantities and measurement units, and the relationship between analytical results and the physico-chemical processes governing soil behaviour.

At the end of the laboratory sessions, students may be asked to prepare a short technical report aimed at critically interpreting the analytical results obtained. The report may form the basis for discussion during the final oral examination.

UNIT 4 – SEMINARS (6 HOURS)

Seminars will address current topics in soil chemistry and the role of soils in agroecosystems, including:

• Soil organic carbon and climate change;

• Roots and the rhizosphere: the role of soil–plant interactions in agroecosystem functioning;

• Soil in Italian and European legislation.

UNIT 5 – PEER INSTRUCTION (4 HOURS)

Collaborative learning activities based on the peer instruction methodology will be integrated throughout the course to promote active participation, stimulate scientific discussion, and consolidate students' understanding of the fundamental concepts of soil chemistry.

These activities are designed to encourage students to compare alternative interpretations, discuss conceptual questions, and develop the ability to reason critically about the physico-chemical processes governing the behaviour of the soil system.

Peer instruction sessions also provide an opportunity for students to assess their own level of understanding and to identify concepts requiring further study before the final examination.

Readings/Bibliography

Adequate preparation for the final examination requires the use of the recommended textbooks together with the teaching materials provided during the course. Additional resources may be made available throughout the semester to complement specific topics covered in lectures, laboratory sessions, and seminars.

Main References

• Sequi P., Ciavatta C., Miano T. (Eds.) (2017). Fondamenti di Chimica del Suolo. Pàtron Editore, Bologna, 295 pp.

• Sparks D.L., Singh B., Siebecker M.G. (2024). Environmental Soil Chemistry. Third Edition. Academic Press, London, 451 pp.

Additional References

• Brady N.C., Weil R.R. (2017). The Nature and Properties of Soils. Fifteenth Edition. Pearson Education, Harlow, 1105 pp.

• Schroeder D., Blume H.P., Brümmer G., Fleige H., Horn R., Kandeler E., Kögel-Knabner I., Kretzschmar R., Stahr K., Wilke B.M. (2016). Soil Science. Springer, Heidelberg, 636 pp.

Teaching Materials

Lecture slides, scientific papers discussed during seminars, technical documents, and additional learning resources will be made available through the University of Bologna Virtuale e-learning platform.

Scientific papers provided during the course are intended to introduce students to current research topics and stimulate critical discussion. They are supplementary learning materials and do not constitute compulsory examination material.

Teaching methods

The course combines lectures, laboratory sessions, seminars, and collaborative learning activities (peer instruction) to progressively guide students from the understanding of soil composition to the interpretation of the physico-chemical processes governing soil behaviour in agricultural and forest systems.

Lectures

Lectures provide the theoretical framework of the course. They introduce the mineral, organic, and fluid components of the soil system and progressively develop the physico-chemical processes that determine soil surface reactivity and soil behaviour.

Particular emphasis is placed on understanding the relationships between soil composition, surface reactivity, and the processes controlling the behaviour of the soil system.

Teaching is primarily process-oriented rather than content-oriented. Throughout the course, conceptual models, diagrams, original figures prepared by the instructor, case studies, and examples drawn from current environmental and agricultural issues will be used to support understanding and stimulate scientific discussion.

Laboratory sessions

Laboratory sessions are designed to apply the theoretical concepts developed during the course to the experimental determination and interpretation of the main chemical properties of soils.

Particular emphasis is placed on the interpretation of analytical data, the correct use of physical quantities and measurement units, and the relationship between analytical results and the physico-chemical processes governing soil behaviour.

Students will become familiar with the principal analytical methods used in soil chemistry laboratories and will develop the ability to interpret laboratory measurements within the broader framework of soil processes.

At the end of the laboratory sessions, students may be asked to prepare a short technical report aimed at critically interpreting the analytical results obtained. The report may form the basis for discussion during the final oral examination.

Participation in laboratory activities is subject to the successful completion of the mandatory health and safety training required by the University of Bologna in accordance with Italian Legislative Decree No. 81/2008 and subsequent amendments. Before attending laboratory sessions, students must have successfully completed Safety Training Modules 1, 2 and 3. Students who do not hold the required certification will not be admitted to laboratory activities. Information on how to access the required safety training modules will be provided through the Degree Programme web site.

Seminars

Seminars will address current topics in soil chemistry and explore the role of soils in sustainable agricultural and forest systems. Their purpose is to connect the fundamental concepts developed during the course with recent advances in research and their applications to the management of agroecosystems.

Recently published scientific papers may be discussed during the seminars as supporting material. These papers are intended to introduce students to current research developments, stimulate critical discussion, and illustrate how fundamental concepts in soil chemistry continue to evolve through research. They are supplementary learning materials and do not constitute compulsory examination material.

Peer instruction

Collaborative learning activities based on the peer instruction methodology will be integrated throughout the course to promote active participation, stimulate scientific discussion, and consolidate students' understanding of the fundamental concepts of soil chemistry.

These activities are designed to encourage students to compare alternative interpretations, discuss conceptual questions, develop critical reasoning skills, and evaluate their own level of understanding throughout the learning process.

Assessment methods

Assessment of learning is based on a final oral examination, conducted jointly for the two modules of the Integrated Course Chemistry and Biochemistry of the Agro-Forest Environment. Students may choose to take the examination in either Italian or English.

The examination covers the topics developed throughout the lectures, laboratory sessions, and seminars of both modules and is designed to evaluate the overall achievement of the intended learning outcomes.

During the examination, students will be expected to demonstrate their ability to:

• explain the composition of the soil system and the properties of its mineral, organic, and fluid components;
• understand the main physico-chemical processes governing soil behaviour;
• apply the concepts and interpretative models of soil chemistry to understand and critically discuss the behaviour of the soil system in different agricultural and forest contexts;
• interpret experimental data and analytical results related to the main chemical properties of soils;
• use appropriate scientific terminology and establish connections between the different topics addressed throughout the course.

For the topics covered in the module Biogeochemistry of Elements in Agricultural and Forest Systems, assessment will follow the same principles, with particular emphasis on the integration of knowledge acquired across the two complementary disciplines.

The final mark reflects the overall level of knowledge, understanding, critical reasoning, and ability to integrate concepts developed throughout the Integrated Course. The final grade is expressed on a 30-point scale and is based on the weighted average of the evaluations assigned to the two disciplinary areas, according to their respective credit allocation (6 ECTS credits each).

The following criteria will be adopted when assigning the final grade:

• 18–21: satisfactory knowledge of the essential concepts and understanding of the main processes discussed during the course;
• 22–25: good knowledge of the subject and ability to establish appropriate connections between the main concepts;
• 26–29: thorough knowledge of the course contents, appropriate use of scientific terminology, and critical interpretation of the processes governing soil behaviour;
• 30–30 with honours: comprehensive and well-integrated knowledge of the discipline, excellent command of scientific terminology, and the ability to apply the interpretative framework of soil chemistry to critically analyse complex situations involving the soil system.

The oral examination normally lasts approximately 30 minutes.

The use of generative Artificial Intelligence tools during the examination is not permitted. Any unauthorized use will be considered a violation of the University's principles of academic integrity.

Students with disabilities or specific learning disorders (SLD) are encouraged to contact the appropriate University services well in advance to arrange any necessary accommodations, while ensuring that the intended learning outcomes of the course are fully assessed.

Teaching tools

The course makes use of a range of teaching resources designed to support the progressive understanding of the processes governing the behaviour of the soil system and to promote meaningful learning.

Lectures are supported by the use of the whiteboard, multimedia presentations, conceptual diagrams, original figures prepared by the instructor, photographs, graphs, and videos illustrating the main physico-chemical processes occurring in soils. These materials are intended to facilitate conceptual understanding and support the construction of an interpretative framework for the soil system.

Laboratory sessions are carried out in the Laboratory of Agricultural Chemistry and Biochemistry, where students become familiar with the principal analytical techniques used to determine the chemical properties of soils and to interpret the resulting analytical data.

Teaching materials, including lecture slides, scientific papers discussed during seminars, technical documents, and additional learning resources, will be made available through the University of Bologna Virtuale e-learning platform.

Generative Artificial Intelligence (AI) tools may be used to support individual study, content revision, and self-assessment. However, students remain fully responsible for developing their own understanding of the subject, critically evaluating the information obtained, and independently interpreting the scientific concepts presented during the course.

Office hours

See the website of Luciano Cavani