08152 - Soil Chemistry

Learning outcomes

After teaching the student possesses the basic knowledge on the genesis of soils, their composition and physico-chemical and biological properties. The information provided makes it easy to understand the mechanisms that regulate the activity of soil surfaces and functions of agro-ecosystems.

Course contents

A) Prerequisites

Students attending this course should have a good knowledge of the basics of mathematics, physics, chemistry, plant biology and agricultural microbiology. Such skills are provided by the basic courses of the first year.

B) Didactic units

1. Soil components (10 hours)

1.1 Soild phase

Mineral components – Minerals, crystals, ionic beams and coordination numbers, silicates, phyllosilicate structure, allophanes, oxides and hydroxides, carbonates.

Organic components – Classification and main transformation processes. Non-humic compounds: carbohydrates, nitrogen compounds, phosphorous compounds, sulphur compounds, lipids. Humic compounds: extraction, fractionation, classification, composition, physico-chemical properties.

Knowledge gained in Didactic Units 1:

• Main soil mineral and organic components chemical and physical characteristics
• Main soil fluid components properties.

2.Soil chemical and physical properties (12hours)

3.1 Chemical properties

Surface properties – Soil particles specific surface, charge source

Adsorption and cationic exchange – Models, double layer thickness and potential, exchange bases, exchange features, cation exchange capacity (CEC), affinity, lyotropic series, exchange equations, dilution effects.

Adsorption and anionic exchange – Soil anions, specific adsorption. Phosphate adsorption, isotherms and equations, dissolution-precipitation mechanisms.

Soil reaction – Soil pH definition, soil pH measurement, active and exchangeable acidity, pH-based soil classification, pH and nutrients, pH and soil biological activities, main buffer systems and soil pH regulation systems.

Knowledge gained in Didactic Unit 3:

• Main parameters linked to soil physical properties and their relationship with chemical properties
• Main theories and processes related to exchange phenomena of soil surface particles and their relationship with soil fertility
• Main processes affecting soil reaction and soil buffer systems
• Relationship between soil reaction and soil fertility

3. Soil biochemistry ( 8 hours)

3.1 Soil as a biological system

Soil organisms – Functional classification, bacteria and residue chain, microbial activity and soil properties

Soil enzymes – Enzyme location, Extra-cellular enzymes classification, stabilization mechanisms, heterogeneous enzymatic catalysis, enzyme properties and functions

3.2 Soil organic matter and its dynamics

Carbon cycle – C sources, degradation, humification and mineralization.

Humification – Theories, enzyme role, carbon mean residence time, carbon balance.

Agronomical function of the organic matter – Effect on soil physical properties, nutritional effects, effects on extra-cellular enzyme activities, pseudo-hormonal activities.

Knowledge gained in Didactic Unit 3:

• Role and functions of soil organisms
• Functional and ecological role of soil extra-cellular enzymes
• Rhizosphere definition and factors linked to its origin
• Processes related to soil carbon cycle

4. Anomalous soils (6 hours)

Acidic soils – Formation, chemical and physical characteristics, correction.

Salt soils – Formation, chemical and physical characteristics, correction.

Sodium soils - Formation, chemical and physical characteristics, correction.

Knowledge gained in Didactic Unit 4:

• Characteristics and correction methods of anomalous soils

6. Exercises (24 hours)

After a preliminary discussion on the importance of performing, in modern agriculture, accurate chemical and physical soil analyses, the exercises take place in the didactic laboratory. Lab activities focus on the determination of some of the main soil properties: texture, reaction, total carbonates, organic matter, cation exchange capacity, salinity and so on. Lab exercises continue with the discussion of the obtained analytical results. Such discussion, related to the themes developed in class lessons, aims at establishing a relationship between the measured physico-chemical parameters and their meaning in terms of soil functionality. At the end of lab exercises students should write a brief report.

Readings/Bibliography

he use of teacher didactic material, provided in the class lectures and online available, besides lessons notes, will be of fundamental importance.

The following book is recommended

AA.VV. Paolo Sequi Coord., Patron Ed. Bologna

Teaching methods

The course is subdivided into two parts:

1) Class lectures: Students should gain the knowledge on the chemical, biochemical and microbiological processes at the basis of soil functioning, through class lectures. Knowledge acquisition and comprehension skills will be constantly monitored, during class lectures, through a continue interaction between the students and the teacher. Such interaction consists in requests by the teacher of discussing some topics of the course, for their impact on current issues linked to the subject of the course, and will aim at developing judgement autonomy and improving communication skills

2) Exercises: Students should attend laboratory experiments, aiming at providing analytical results for the investigation of chemical and biological processes related to a certain soil. Such part of the course will also aim at verifying the ability of applying the theoretical knowledge about the managing of soils.

Assessment methods

Assessment of learning for the Soil Chemistry module, for students of Agricultural Technologies, takes place through a final oral examination, conducted jointly with the assessment of the other module that completes the Integrated Course (Agricultural Biochemistry and Soil Fertility). The oral examination will cover the topics addressed in the lectures of the two modules. Two basic questions will be asked, one for each thematic area: soil chemistry, and agricultural biochemistry and soil fertility. Starting from this structure, appropriate further discussion will follow on the topics covered.

The assessment must be passed as a whole, and the candidate must achieve a mark of at least 18 out of 30 in each of the disciplinary areas characterising this integrated course.

The examination is taken with one of the lecturers responsible for the integrated course, and the final mark is expressed out of 30.

Assessment criteria

18–19: essential knowledge of the fundamental topics; limited ability to make connections between the different processes and acceptable use of scientific terminology.

20–24: adequate knowledge of the topics covered; ability to correctly describe the main processes and to make simple connections between soil properties, plant nutrition and metabolism.

25–27: good knowledge of the topics; ability to integrate the different aspects of the course and to correctly interpret the relationships between soil, plant and environment.

28–30: in-depth and critical knowledge of the course content; ability to effectively connect the chemical, biochemical and nutritional processes that regulate the functioning of agricultural and forest ecosystems; full command of disciplinary language.

30 with honours: excellent preparation, ability to develop independent reasoning and critical synthesis, rigorous use of scientific terminology, and ability to discuss in an integrated and in-depth manner the relationships between soil fertility, plant metabolism, productivity and sustainability.

With regard to assessment, the use of generative Artificial Intelligence is not applicable to the in-person oral examination. Any preparatory materials produced using AI tools remain the responsibility of the student and do not replace the necessary independent acquisition of the knowledge required to pass the examination.

Students with Specific Learning Difficulties (SpLD) or temporary or permanent disabilities are invited to contact the relevant University office promptly in order to agree on any adjustments to the examination, in compliance with the learning objectives of the course.

Teaching tools

Overhead projector, personal computer and projector will be used for class lectures.

Laboratory exercises will take place in the didactic laboratories of Agricultural Chemistry and Biochemistry.

Office hours

See the website of Claudio Marzadori