Beaudoin, Nicolas (2006) Experimental analysis and modelling of the effects of cropping practices on nonpoint nitrate pollution of a deep aquifer in an arable farming area. PhD thesis Agronomie et environnement, INRA - Unité d'agronomie Laon-Reims-Mons, INAPG 2006INAP0028 p.208.

Full text available as: - Beaudoin_Nicolas_2006_these.pdf ( 7329 Kb )

Licence: Copyright

Abstract

Surface and groundwaters must regain good chemical and biological quality before 2015 according to

European Directives. Good Agricultural Practices (GAPs) establish a compromise between the risks of

pollution and the loss of revenue. The minimum result expected is conformity with the drinking water standard

of 50 mgNO3.L-1 in the collected water and the avoidance of transfer of pollution from the hydrosphere into

the atmosphere. However their implementation does not guarantee that these objectives will be reached ; that

requires a means of quantifying the impact of effective agricultural practices on nitrate pollution. We have

tested different methods of quantification by using data from a collaborative experiment on pollution

prevention, carried out on the site of Bruyères (02). The question targeted was « what is the impact of GAP,

applied regularly, on the scale of a catchment area ? » The research question was « can nitrate pollution be

modelled, in a farming situation, on the scale of a catchment area ? »

The study site is a plateau of 187 ha which supplies a groundwater aquifer located in the Lutetian

geological layer. This aquifer feeds five main springs which have suffered increasing pollution since 1970.

The 21 cultivated fields on the plateau were subjected to regular implementation of GAPs by the three farmers

since 1990. The farming practices and the hydrogeology of the site were characterised. The flow rates of the

springs respond to effective rainfall after a delay of a week. The mean residence time of the tritium molecule

in the aquifer is 25 years, because of the thickness of the unsaturated zone. In view of this delay, an

intermediate level of evaluation is necessary : the losses under the root zone. The methods of quantification

differ according to their degree of dependence on the experimental data : i) the LIXIM mathematical model,

associated with all the observed data ; ii) a stochastic model of crop response to the nitrogen rate, initialised

each year, iii) the functional dynamic model STICS, which can simulate the losses of the soil/plant/atmosphere

system continuously over several years. The predictions of the variables of economic and environmental

interest are compared with the observed data on the scale of the station and of the basin. The environmental

and economic impacts for different scenarios of pollution prevention are simulated.

The mineral nitrogen residues at harvest and at the beginning of winter are similar and stable over time

at 41 et 57 kgN.ha-1 respectively. The averaging of the losses, calculated with LIXIM, over the crop rotation,

smooths out the crop factor and makes the soil type the principal determinant of the concentration. The mean

weighted nitrate concentration in the percolating water is 46 mgNO3.L-1 for the cultivated zone and 37

mgNO3.L-1 for the whole basin. This good result is confirmed qualitatively by the fall observed in the contents

at several collection points since the year 2000. The response time of the aquifer would be equal to half of its

renewal time. The reduction in the nitrate content of the percolation water permitted by GAPs, compared with

a conventional scenario, is between 27 and 39%, depending on the simulation method. The cost of the GAPs is

0.07 €.m-3 of drinked water, making prevention competitive with water treatment at the Bruyères site.

Dynamic modelling with STICS appears to be effective in the agricultural situation, but its reliability

depends on the availability and relevance of the databases used to calibrate it. It can take account of a large

number of technical inputs and their long-term interactions. Coupling STICS with a geographical information

system (GIS) enables the spatial variability of the physical and cultural features of the environment to be

integrated. However it is not possible to guarantee the reliability of the predictions for both any time and any

place. Access to the precise value of parameters like the crop’s maximum rooting depth or the stock of organic

nitrogen is simply not feasible. According to the STICS model, the nitrogen losses simulated in gaseous form

are equal to those in solution. This result needs to be verified. Bearing in mind these limitations, modelling

based on experimentation can become a management tool for nitrogen in cropping systems on a regional scale.

The problem of limiting nitrate leaching is shifted towards the conception of sustainable cropping systems.

Table of content

Avant propos et remerciements…………………………………………………..…………..……3

Cadrage…………………………….………………….…………………………………..……….9

1 Introduction_____________________________________________________________ 11

1.1 La problématique de la pollution nitrique des eaux souterraines______________________ 13

1.1.1 Contexte _______________________________________________________________________ 13

1.1.1.1 Contexte agricole et para-agricole _______________________________________________ 13

1.1.1.2 Contexte agri-environnemental _________________________________________________ 14

1.1.2 La pollution nitrique des eaux souterraines_____________________________________________ 15

1.1.3 Les cycles concernés ______________________________________________________________ 18

1.1.3.1 Le cycle de l'eau _____________________________________________________________ 18

1.1.3.2 Les cycles biologiques ________________________________________________________ 18

1.1.3.3 Le cycle du carbone __________________________________________________________ 18

1.1.3.4 Le cycle de l'azote ___________________________________________________________ 18

1.1.4 Les systèmes impliqués____________________________________________________________ 20

1.1.4.1 Les systèmes hydrologiques ____________________________________________________ 20

1.1.4.2 Les agro - écosystèmes________________________________________________________ 22

1.1.4.3 Le système sol - culture - atmosphère ____________________________________________ 23

1.1.5 L’organisation de la prévention______________________________________________________ 25

1.1.6 Problématiques __________________________________________________________________ 26

1.1.6.1 Problématique agricole________________________________________________________ 26

1.1.6.2 Problématique environnementale ________________________________________________ 27

1.1.6.3 Problématique scientifique _____________________________________________________ 27

1.2 Objectifs, hypothèses et étapes de la thèse ________________________________________ 29

1.2.1 Les objectifs finalisés _____________________________________________________________ 29

1.2.2 Les questions de recherche _________________________________________________________ 29

1.2.3 Le support de recherche ___________________________________________________________ 29

1.2.4 L’expérimentation partenariale ______________________________________________________ 29

1.2.5 Les modèles de simulation « sol-culture-atmosphère »____________________________________ 30

1.2.6 Hypothèses d’étude _______________________________________________________________ 31

1.2.7 Démarche d’étude ________________________________________________________________ 31

1.2.8 Les étapes ______________________________________________________________________ 32

2 . Quantification expérimentale du lessivage du nitrate dans un bassin hydrologique___ 33

2.1 Nitrate leaching in intensive agriculture in Northern France: effect of farming practices,

soils and crop rotations. __________________________________________________________________ 35

2.1.1 Introduction_____________________________________________________________________ 35

2.1.2 Materials and Methods ____________________________________________________________ 36

2.1.2.1 Experimental site ____________________________________________________________ 36

2.1.2.2 Methods ___________________________________________________________________ 38

2.1.3 Results_________________________________________________________________________ 39

2.1.3.1 Crop response to GAP and AEP_________________________________________________ 39

2.1.3.2 Water and nitrogen contents____________________________________________________ 41

2.1.3.3 Water and nitrogen fluxes _____________________________________________________ 44

2.1.3.4 Cumulative fluxes____________________________________________________________ 47

2.1.4 Discussion ______________________________________________________________________ 50

2.1.5 Conclusion _____________________________________________________________________ 51

5

2.2 Effet des Bonnes Pratiques Agricoles sur l'évolution des teneurs en nitrate à l'exutoire d'un

aquifère tertiaire du Bassin parisien ________________________________________________________ 53

2.2.1 Introduction_____________________________________________________________________ 54

2.2.2 Matériel et méthodes ______________________________________________________________ 55

2.2.2.1 Le site expérimental __________________________________________________________ 55

2.2.2.2 Mesures expérimentales _______________________________________________________ 59

2.2.2.3 Calculs ____________________________________________________________________ 61

2.2.3 Résultats et discussion_____________________________________________________________ 63

2.2.3.1 Flux d’eau et d’azote à l’entrée de l'aquifère _______________________________________ 63

2.2.3.2 Caractérisation des matériaux et solutés en sous sol _________________________________ 66

2.2.3.3 Flux d’eau et d’azote à l’exutoire________________________________________________ 68

2.2.3.4 Stocks d’eau et temps de renouvellement__________________________________________ 71

2.2.3.5 Etude des transferts internes____________________________________________________ 72

2.2.4 Conclusion _____________________________________________________________________ 76

2.3 Conclusion partielle___________________________________________________________ 77

3 Simulation d'impacts de scénarios techniques aux échelles annuelle et du bassin

hydrologique ________________________________________________________________ 79

3.1 Simulation de l’impact de différents scénarios agronomiques sur les pertes de nitrate à

l’échelle d’un bassin hydrologique__________________________________________________________ 81

3.1.1 Introduction_____________________________________________________________________ 81

3.1.2 Matériels et méthodes _____________________________________________________________ 82

3.1.2.1 Principe général _____________________________________________________________ 82

3.1.2.2 Le modèle 1 ________________________________________________________________ 84

3.1.2.3 Le modèle 2 ________________________________________________________________ 84

3.1.2.4 L'enchaînement des 2 modèles __________________________________________________ 86

3.1.2.5 Le site expérimental de Bruyères ________________________________________________ 86

3.1.2.6 Les scénarios évalués _________________________________________________________ 86

3.1.2.7 Les simulations réalisées avec STICS ____________________________________________ 87

3.1.2.8 Expression des résultats _______________________________________________________ 87

3.1.3 Résultats _______________________________________________________________________ 88

3.1.3.1 Evaluation des modèles à l’échelle de la parcelle homogène ___________________________ 88

3.1.3.2 Evaluation du modèle à l'échelle du bassin ________________________________________ 90

3.1.3.3 Comparaison des 4 principaux scénarios __________________________________________ 92

3.1.3.4 Comparaison des 8 scénarios élémentaires_________________________________________ 93

3.1.3.5 Effets des différents types de sols________________________________________________ 94

3.1.4 Discussion ______________________________________________________________________ 95

3.1.4.1 Validité des résultats obtenus ___________________________________________________ 95

3.1.4.2 Généralisation des résultats obtenus______________________________________________ 97

3.2 Agricultural water nonpoint pollution control under uncertainty and climate variability _ 99

3.2.1 . Introduction____________________________________________________________________ 99

3.2.2 . The model ____________________________________________________________________ 100

3.2.2.1 . Costs of scenarios__________________________________________________________ 101

3.2.2.2 . Nitrate concentration in drained water __________________________________________ 101

3.2.2.3 . Optimal scenario___________________________________________________________ 102

3.2.3 . Illustration ____________________________________________________________________ 102

3.2.3.1 . Data ____________________________________________________________________ 103

3.2.3.2 . Scenarios simulated ________________________________________________________ 104

3.2.3.3 . Modelling ________________________________________________________________ 105

3.2.4 . Results_______________________________________________________________________ 106

3.2.4.1 . Probabilistic cost-effectiveness in the long term. __________________________________ 106

3.2.4.2 . Probabilistic cost-effectiveness under climate variability ___________________________ 108

3.2.5 . Discussion ____________________________________________________________________ 109

3.3 Conclusion partielle__________________________________________________________ 111

6

4 Simulation de l’impact de pratiques agricoles sur les pertes de nitrate à l’échelle de la

rotation et du bassin hydrologique _____________________________________________ 113

4.1 Soil-crop model STICS evaluation for continuous 8 year time course simulations against an

“on farm” soil- crop database_____________________________________________________________ 115

4.1.1 Introduction____________________________________________________________________ 115

4.1.2 Materials and methods ___________________________________________________________ 116

4.1.2.1 Model ____________________________________________________________________ 116

4.1.2.2 Experimental site ___________________________________________________________ 117

4.1.2.3 Databases _________________________________________________________________ 119

4.1.2.4 Model Inputs_______________________________________________________________ 120

4.1.2.5 Model evaluation ___________________________________________________________ 120

4.1.3 Results________________________________________________________________________ 121

4.1.3.1 Model parameterization ______________________________________________________ 121

4.1.3.2 Evaluation of the calibrated model______________________________________________ 123

4.1.3.3 Model validation with reset or continuous simulation _______________________________ 127

4.1.3.4 Sensitivity analysis __________________________________________________________ 128

4.1.3.5 Model predictions vs soil type and RS/CS option __________________________________ 131

4.1.4 Discussion _____________________________________________________________________ 132

4.1.4.1 Impact of quality of databases on performances ___________________________________ 132

4.1.4.2 Impact of the time course of the simulation _______________________________________ 133

4.1.4.3 Need of improvement of the model _____________________________________________ 134

4.1.5 Conclusion ____________________________________________________________________ 135

4.2 Prédictions d'impacts de scénarios techniques ____________________________________ 137

4.2.1 Objectifs ______________________________________________________________________ 137

4.2.2 Méthode de comparaison _________________________________________________________ 137

4.2.3 Simulation d'impacts du scénario BPA_______________________________________________ 137

4.2.4 Simulation d'impacts du scénario sans CIPAN _________________________________________ 139

4.2.5 Simulation d'impacts du scénario Conventionnel _______________________________________ 139

4.2.6 Conclusions____________________________________________________________________ 139

4.3 Couplage de STICS 6 au SIG Arc Info et sensibilité des prédictions au niveau de résolution

de la carte des sols ______________________________________________________________________ 140

4.3.1 Introduction____________________________________________________________________ 140

4.3.2 Matériel et méthodes _____________________________________________________________ 141

4.3.2.1 Principe du couplage ________________________________________________________ 141

4.3.2.2 Etablissement d'une carte typologique dite carte simplifiée___________________________ 141

4.3.2.3 Etablissement de règles de pédotransfert _________________________________________ 143

4.3.2.4 Règles d'apparentement des valeurs initiales ______________________________________ 145

4.3.2.5 Simulation à 3 niveaux de résolutions ___________________________________________ 145

4.3.3 Résultats ______________________________________________________________________ 145

4.3.3.1 Valeurs à l'échelle de l'unité de simulation________________________________________ 145

4.3.3.2 Prédictions à l'échelle parcellaire _______________________________________________ 146

4.3.3.3 Prédictions à l'échelle du bassin ________________________________________________ 147

4.3.4 Discussion _____________________________________________________________________ 150

4.3.5 Conclusions et perspectives _______________________________________________________ 151

4.4 Conclusion partielle__________________________________________________________ 152

5 discussion générale ______________________________________________________ 153

5.1 discussion sur les méthodes ___________________________________________________ 155

5.1.1 Atouts et limites du dispositif expérimental ___________________________________________ 155

5.1.2 Hypothèses sur les conditions expérimentales _________________________________________ 155

5.1.2.1 Sur la démarche d'expérimentation agricole partenariale _____________________________ 155

5.1.2.2 Sur la hiérarchie des pertes d'azote______________________________________________ 156

5.1.2.3 Sur le devenir du nitrate au sein du système hydrologique ___________________________ 157

5.1.3 Hypothèses sur les outils de quantification ____________________________________________ 157

5.1.3.1 Sur les conséquences des conditions 'on farm' _____________________________________ 157

5.1.3.2 Sur la méthode de spatialisation des flux _________________________________________ 157

5.1.3.3 Sur le type de modélisation agronomique ________________________________________ 158

5.2 Discussion sur les déterminants de la pollution ___________________________________ 159

7

5.2.1 Indicateurs de risque ou de sensibilité du milieu à la lixiviation____________________________ 159

5.2.1.1 Introduction _______________________________________________________________ 159

5.2.1.2 Indicateur de pression polluante________________________________________________ 159

5.2.1.3 Indicateur de sensibilité du milieu à la lixiviation __________________________________ 160

5.2.2 Facteurs d'échelles temporelle et spatiale _____________________________________________ 163

5.2.2.1 Facteur d’échelle temporelle et effets cumulatifs ___________________________________ 163

5.2.2.2 Facteur d’échelle spatiale _____________________________________________________ 163

5.2.3 Impacts de l’agriculture intensive ___________________________________________________ 164

5.2.3.1 Introduction _______________________________________________________________ 164

5.2.3.2 Pratiques techniques isolées et pertes en nitrate ____________________________________ 164

5.2.3.3 Systèmes de culture et pertes en nitrate __________________________________________ 166

5.2.3.4 Devenir du nitrate dans les couches géologiques ___________________________________ 168

6 conclusions et perspectives ________________________________________________ 171

6.1 Conclusions ________________________________________________________________ 173

6.1.1 Démarche _____________________________________________________________________ 173

6.1.2 Bilan des questions agri-environnementales ___________________________________________ 173

6.1.3 Bilan des questions scientifiques____________________________________________________ 174

6.1.4 Bilan des méthodes ______________________________________________________________ 175

6.2 Perspectives ________________________________________________________________ 176

6.2.1 Expérimentation partenariale ______________________________________________________ 176

6.2.2 Méthodes______________________________________________________________________ 176

6.2.3 Questions scientifiques ___________________________________________________________ 176

6.2.4 Questions agri-environnementales et sociétales ________________________________________ 177

7 Bibliographie___________________________________________________________ 179

8 Plan des annexes________________________________________________________ 193

9 Résumé (au verso)_______________________________________________________ 209

Statistiques de consultation

Repository Staff Only: edit this item