Cosentino, Diego Julian (2006) Organic matter contribution to aggregate stability in silty loam cultivated soils. carbon input effects. PhD thesis Matières organiques du sol, AgroParistech 2006INAP0041 p.186.
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Abstract
Soil aggregate stability is a key property for soil functioning. However, there are still no tools to
predict its temporal variations or to determine cultural practices to improve it. The subject is particularly
important in regard to the effect of C inputs to fragile soils (silty cultivated soils).
The general aim of this work is to improve the knowledge in factors determining short-time
aggregate stability variations caused by C inputs and soil water contents variations.
To establish quantitative relationships among aggregate microbial agents, elementary physical
properties that determine aggregate stability (porosity, hydrophobicity and soil cohesion) and aggregate
stability we varied the organic matter added rate (maize residue) and wetting-drying cycles in soil controlled
conditions. We used three aggregate stability tests that distinguish different soil breakdown mechanisms
(slaking, microcracking and mechanical breakdown) to analyze the relationships from a mechanistic point of
view.
In our conditions, C inputs stimulated linearly microbial activity and by-products to all doses of C
inputs used. Aggregate microbial agents measured (microbial biomass-C, ergosterol content (biomarquer of
fungi), and hot water extractable polysaccharides (surrogate of extracellular polysaccharides)), had an
important dynamic pattern and there were all correlated to aggregate stability. No hierarchic order among
biological variables could be established. Aggregate stability to slaking, microcracking and mechanical
breakdown had a similar dynamic pattern after C input. A linear semi-mechanistic model predicting
aggregate stability variations based on coupling an soil C and N dynamic model (CANTIS) and multiple
linear regressions linking microbial biomass-C and respired CO2 after a C input and aggregate stability was
proposed.
C input has also strongly modified the elementary physical properties that determine aggregate
stability. The aggregates increased porosity, hydrophobicity and Interparticle cohesion with C input rate.
Giving the impact of microbial activity in hydrophobicity, emphasis was given in determining
hydrophobicity and three methods were applied and evaluated. Diversity of microbial activity effects on soil
physical aggregate properties suggests that is still pertinent to consider aggregate stability as an integrative
and sensitive property to organic matter input effects in soil.
Climatic conditions as wetting-drying cycles have shown to modulate the effect of C inputs on
aggregate stability, particularly changing the relative impact of the organic matter in breakdown mechanisms
of aggregate stability.
| Item Type: | PhD Thesis (PhD) |
|---|---|
| PhD Supervisor: | Chenu, Claire |
| Date: | 15 December 2006 |
| Board of examiners: | Tessier, Daniel and Caron, Jean and Nicolardot, Bernard and Boivin, Pascal and Hallett, Paul and Menasseri, Safya |
| Ecole Doctorale: | ED 435 AGRICULTURE, ALIMENTATION, BIOLOGIE, ENVIRONNEMENTS ET SANTE |
| Discipline: | Matières organiques du sol |
| Collection (Fonds): | AgroParistech |
| Institution: | AgroParistech |
| Subjects: | 8. Earth Sciences and Environmental Engineering |
| Uncontrolled Keywords: | Aggregate stability, Stabilité structurale, Hydrophobicity, Hydrophobie, Cohesion, Cohésion, Aggregate microbial agents, Agents microbiens, C inputs, Apport de matières organiques, Maize residues, Résidus de maïs, Microbial biomass carbon, Carbone de la biomasse microbienne, Slaking, éclatement, Microcracking, Microfissuration, Mechanical breakdown, Désagrégation mécanique |
| ID Code: | 4754 |
| Deposited By: | Marina Briffaut |
| Deposited On: | 11 February 2009 |
Table of content
Chapitre Premier - 1
1 Motivation de la thèse. Contexte - 3
2 Objectif général de la thèse - 4
3 Organisation du mémoire - 4
4 Structure du Sol. Etat de connaissances - 5
4.1 Un carrefour complexe du fonctionnement du sol - 5
4.2 Définitions - 9
4.2.1 Forme structurale - 9
4.2.2 Stabilité structurale - 9
4.2.3 Résilience structurale - 10
4.3 Agrégats vs structure - 11
4.4 Mécanismes impliqués dans la macroagrégation - 12
4.4.1 Mécanismes de destruction des agrégats ou désagrégation - 12
4.4.1.1 L’éclatement - 12
4.4.1.2 La microfissuration par gonflement différentiel - 13
4.4.1.3 La désagrégation mécanique sous l'impact des gouttes de pluie - 13
4.4.1.4 La dispersion physico-chimique - 14
4.4.2 Mécanismes de stabilisation des macroagrégats - 15
4.4.2.1 Collage « Gluing » - 15
4.4.2.2 Enrobage par des microorganismes filamenteux («Physical
Entanglement») - 16
4.4.2.3 Hydrophobie - 19
4.4.2.4 Système poral - 20
4.5 Méthodes d’évaluation de la stabilité de la structure - 21
4.6 Dynamique de la stabilité de la structure à court terme - 25
4.6.1 Les cycles de dessiccation – réhumectation - 25
4.6.2 L’étroite relation des dynamiques des matières organiques, de l’activité
de microorganismes et de la stabilité de la structure - 25
x
4.7 Relations quantitatives entre l’apport de la MO, l’activité microbienne et la
stabilité de la structure à court terme - 26
5 Objectifs spécifiques et démarche de la thèse - 29
5.1 Objectifs - 29
5.2 Démarche - 31
Chapitre 2 - 33
1 Introduction - 36
2 Materials and methods - 39
2.1 Study area, site description and sampling - 39
2.2 Added organic matter - 40
2.3 Incubation procedure - 40
2.4 Soil analyses - 41
2.5 Aggregate stability tests - 42
2.6 Modelling residue decomposition with CANTIS - 42
2.7 Modelling aggregate stability - 44
2.8 Statistical analysis - 46
3 Results - 46
3.1 Microbial activity, biomass and by-products - 46
3.2 Aggregate stability - 52
3.3 Relationships between aggregate stability and microbial variables - 55
3.4 Simulation of straw decomposition with CANTIS - 57
3.5 Aggregate stability model - 58
4 Discussion - 64
4.1 Impact of C inputs on microorganisms - 64
4.2 Relation of aggregate stability to C inputs - 65
4.3 Biological variables determining aggregate stability - 67
4.4 Predicting aggregate stability with time - 68
5 Summary and conclusions - 70
Chapitre 3 - 71
1 Introduction - 74
2 Materials and methods - 76
2.1 Samples - 76
2.2 Aggregate porosity - 77
2.3 Water drop penetration time (WDPT) - 77
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2.4 Capillary rise method (CRM) - 77
2.5 Water-repellency index (R) - 79
3 Results and discussion - 80
3.1 Developed hydrophobicity - 80
3.2 Relationships between results obtained by the different methods - 81
3.2.1 WDPT and R - 82
3.2.2 R and the soil-water apparent contact angle - 86
3.2.3 WDPT and the apparent contact angle - 86
3.3 Porosity - 88
3.4 Practical aspects - 90
4 Conclusions - 93
Chapitre 4 - 95
1 Introduction - 98
2 Materials and methods - 100
2.1 Experimental area, site description and sampling procedure - 100
2.2 Incubations procedures and experimental treatments - 101
2.3 Soil analyses - 101
2.3.1 Biological variables - 102
2.3.2 Water drop penetration time (WDPT) - 102
2.3.3 Water-repellency index (R) - 103
2.3.4 Aggregate porosity - 104
2.3.5 Tensile strength and uniaxial compression (oedometer test) - 104
2.3.6 Aggregate stability - 106
3 Results - 106
3.1 Water uptake and hydrophobicity - 106
3.2 Poral system - 109
3.3 Cohesion - 111
3.4 Aggregate stability - 113
3.5 Biological variables - 117
4 Discussion - 117
4.1 Porosity - 117
4.2 Hydrophobicity - 118
4.3 Cohesion - 120
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4.4 Contribution of the different aggregate physical properties to the extent of
slaking, mechanical breakdown and differential swelling - 122
4.4.1 Slaking - 122
4.4.2 Mechanical breakdown - 125
4.4.3 Differential swelling - 126
5 Conclusions - 128
Chapitre 5 - 129
1 Introduction - 132
2 Materials and methods - 134
2.1 Soil and sampling - 134
2.2 Incubation and experimental treatments - 135
2.3 Measurements - 136
2.4 Aggregate stability - 137
2.5 Statistical analyses - 137
3 Results - 138
3.1 Biological variables - 138
3.2 Aggregate stability and water drop penetration time - 141
4 Discussion - 146
4.1 Effect of organic matter addition on aggregate stability - 146
4.2 Microbial agents of aggregate stability - 148
4.3 Dry-wet cycles net effects - 149
4.4 Conclusions - 151
5 Acknowledgements - 152
Chapitre 6 - 153
1 Conclusions générales - 155
1.1 La démarche et le système - 156
1.2 Les compartiments microbiologiques du modèle conceptuel - 158
1.3 Les compartiments des propriétés physiques élémentaires qui déterminent la
stabilité structurale - 160
Liste bibliographique unique - 165
Valorisation de ce mémoire dans des réunions scientifiques - 183
General abstract (version anglaise) - 185
Résumé général (french version) - 186
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