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Water management in rural South India and Sri Lanka

 | 
Patrice Cohen
, 
S. Janakarajan

Part III. Legal and ecological settings in water management

9. Soils and Water: the Small Watersheds Approach

Pierre Curmi

Texte intégral

Introduction

1Social water management in rural area must take into account the fact that the physical environment in which these social systems evolve is itself a spatially organized system: an ecosystem. It means that the different parts of the territory will have specific characteristics and potentialities. They interact and exchange fluxes (water, solid or dissolved elements) and a local intervention in one part of the system will have consequences elsewhere in the system even relatively far from it. In order to understand how the characteristics of an ecosystem may direct the organization of a society or how human activity may modify the natural system evolution – by improving or degrading it – it is necessary to conduct a multidisciplinary approach which integrates these two systemic representations: the ecological one and the social one.

2The ongoing research at the FIP Soil Science Laboratory deals with the role of the soil and the agricultural practices on the water cycle and their incidence in ecosystem evolution. Two research projects are undertaken at two different spatial and temporal scales:

  1. “The Small Watersheds Project” adopts an approach based on imbricated catchments from large river basins to elementary catchments and considers very long time periods;
  2. the second project uses an approach based on relationships between soil systems and farming systems at the scale of the rural community and deals with medium-term evolutions.

The Small Watersheds Project

3The objectives of the Small Watersheds Project are:

  1. to study the effects of climatic drainage and human activities on the dynamics of the biogeochemical and hydrological cycles in small watersheds and rivers to get better knowledge of the processes acting in continental formations and governing the quality of surface and ground waters in tropical river systems;
  2. to establish the physical and chemical erosion balance at different scales to elaborate hydro-geochemic al models predicting also the evolution of specific tropical soilscapes.

4This project was initiated by the French “Institut de Recherche pour le Développement” (IRD) and the Civil Engineering Department of the Indian Institute of Science, Bangalore (IISc) which are associated in the Indo-French Cell for Water Sciences (IFCWS) to cooperate on environmental problems concerning water quality and water management in South India, with the collaboration of the French Institute of Pondicherry (FIP) due to its expertise in soils and vegetation (Gunnell and Bourgeon 1997; Gunnell 1999).

5The study site is the Kabini basin on the back slope of the Western Ghats (south-west of Bangalore). This site shows two important features making it an outstanding site to study weathering and erosion mainly controlled by climatic drainage and human activity. It allows of the choice of small watersheds along a climatic gradient with contrasted land use on the same geological basement.

6(i) On gneisses basement, the site comprises, from west to east, three major weathering and pedogenesis zones related to a rainfall gradient (from 3000 mm to 500 mm annual rainfall): (1) a ferrallitic humid zone to the west showing a landscape with half-orange-shaped hills with coffee plantations and flat-bottomed valleys with paddy fields (Figure 9.1), (2) a forested transition zone (Bandipur Reserved Forest) and (3) a semi-arid fersiallitic zone to the east with a gently sloping landscape with rock outcrops showing rainfed crops (jowar, coton, groundnuts, etc.) and few irrigated crops (sugar cane, turmeric, etc.) (Figure 9.2).

Figure 9.1: Soils and landscape in the humid area

Source: Diagramme block source: Gunnell Y. et Bourgeon G., 1997.

Figure 9.2: Soils and landscape in the semi-arid area

Source: Diagramme block source: Bourgeon G., 1991.

7(ii) Three major tributaries of the Kabini flowing south to north drain these three zones which are thus defined by very contrasting flows and distinct mineralogical associations: (1) the Upper Kabini with a permanent flow in the humid zone draining ferrallitic environment (total exportation of bases and partial exportation of silica: residual accumulation of kaolinite, iron and aluminium oxides), (2) the Heb Halla with a seasonal flow in the transition zone, and (3) the Gundal with a sporadic flow in the semi-arid zone draining fersiallitic environment (limited export of bases and silica: residual accumulation of 1/2 minerals, carbonates, etc.).

8It is planned to undertake multidisciplinary studies (geophysics, pedology, mineralogy, hydrology, and geochemistry). They will integrate both structural studies on the physical environment as well as studies on the hydrogeochemical functioning of soil-water systems. Investigations are planned at different scales, from the local scale of the small hydro – pedological units (elementary watershed) up to the regional scale represented by the Kabini basin, passing through the medium scale of its major tributaries.

Relationships between soil systems and farming systems with irrigation by rain feeding reservoirs

9The study of the relationships between soil systems and farming systems raises the two following research questions:

  1. How do soil constitution, behaviour and spatial distribution influence the farming system? The response to this question “give (s) explicit recognition to the ecological and territorial dimension of all social structure” (D. Mosse 1997);
  2. How do agricultural practices modify present soil functioning and long term evolution? This question evaluates the sustainability of the system.

10The farming systems studied are irrigated by rain fed reservoirs, a multi-secular practice in the semi-arid zones which was neglected in the past decades and is presently a subject of renewed interest in sustainable water management practices. This implies a multidisciplinary approach including the collaboration of the FIP Social Sciences Department and the French “Centre National d’Etudes Agronomiques des Regions Chaudes” (CNEARC) for present and historical characterizations of farming systems at the scale of the rural community (Lacarce and Fleutry 2001; Bouzid and Perdrier 2001).

How do soil constitution, behaviour and spatial distribution influence the fanning system?

11The analysis will be performed using spatial representations. How the farmers perceive soil behaviour differences will be checked comparing soil maps and farmer’s mental maps. The extent to which crop types are determined by the soil properties will be estimated by comparison between soils map and cropping pattern.

How do agricultural practices modify present soil functioning and long term evolution?

12The modification of the physical properties of soil and organic matter content due to agricultural practices leads to a decrease in soil quality and water efficiency. Therefore, organic matter type and content, structure of the topsoil layers and its evolution with climatic conditions are chosen as indicators of the interaction between soil systems and farming systems. The organization of this interface layer between soil and atmosphere will determine water input in the soil system by governing the balance between infiltration and runoff. Moreover, it will play a role in the dynamics of weathering and pedogenesis by modifying the water balance terms and by rejuvenating the surfaces.

13The methodology used will compare pairs of contrasted situations (different practices on the same soil or the same practice on different soils) combining inquiries made of farmers to get a precise identification of the different cultural operations performed and the quantification of the structural organization of the ploughed layer. The work of French soil scientists on the typology of surface crust morphology (Boiffin et al. 1988; Cazenave and Valentin 1989) and on the structure of the ploughed layers (Roger-Estrade et al. 2000) will give the framework of this quantification.

Conclusion

14These two research programmes will provide complementary data. We can expect that the Small Watershed Project will help to understand the natural functioning of the watersheds and the water cycle in the different bioclimatic areas by studying the mechanisms of chemical water composition formation and by the balance of elements. While the second programme will attempt to propose technical improvements to ensure the sustainability of the farmers’ practices by an indepth analysis of interactions between soil systems and farming systems. For example, the study of the irrigation farming systems in the Kaliveli tank region (Tamil Nadu) (Lacarce and Fleutry 2001; Bouzid and Perdrier 2001) showed that the farmers using few machines of low power degraded only slightly the physical properties of the soils. On the other hand, a decrease in stock breeding – which is not related to the physical environment but to political and economical reasons – leads to a lower restitution of organic matter to the soil and therefore causes an important decrease in fertility. It will be suitable to encourage in this case a certain level of breeding and to develop any form of organic matter restitution to the soil.

Bibliographie

References

Boiffin, J., Papy, F., M. Eimberck, 1988. “Influence des systèmes de culture sur les risques d’érosion par ruissellement concentre. I – Analyse des conditions de déclenchement de l’erosion”, Agronomic, 8, 663-673.

Bouzid, M., and A. Perdrier, 2001. “Intensification et gestion durable des ressources en eau et en sol. Un système agraire en transition en zone semi-aride, etude de trois villages du Tamil Nadu (Inde du Sud)”, DAA de l’ENSAM et de l’INAPG respectivement et DAT du cycle ESAT1 du CNEARC, Institut Français de Pondichéry, 113 pp. + annexes.

Casenave, A., and C. Valentin, 1989. Les états de surface de la zone sahelienne. Influence sur l’infiltration, ORSTOM, Coll. Didactique, 229pp.

Gunnell, Y., 1999. “Systèmes agraires et facettes écologiques en Karnataka (Inde du Sud): portraits d’une organisation humaine autour d’un gradient bioclimatique exceptionnel”, Annales de Géographie, 605, 46- 66.

Gunnell. Y., and G. Bourgeon, 1997. “Soils and climatic geomorphology on the Karnataka Plateau, peninsular India”, Catena, 29, 239-262.

Lacarce E. and L. Fleutry, 2001. “Systèmes pédologiques et systèmes agraires en conditions d’irrigation par tanks pluviaux en Inde du Sud (Tamil Nadu)”, DAA Génie de l’Environnement, ENSA Rennes, Institut Français de Pondichéry, 19 p. + annexes.

Mosse, D., 1997. “The symbolic making of a common property resource: history, ecology and locality in a tank- irrigated landscape in South India”, Development and Change, Vol. 28, 467-504.

Roger-Estrade, J., Richard, G., H. Manichon, 2000. “A compartmental model to simulate temporal changes in soil structure under two cropping systems with annual mouldboard ploughing in a silt loam”, Soil and Tillage Research, 54, 41-53.

Table des illustrations

Légende Figure 9.1: Soils and landscape in the humid area
Crédits Source: Diagramme block source: Gunnell Y. et Bourgeon G., 1997.
URL http://books.openedition.org/ifp/docannexe/image/10145/img-1.jpg
Fichier image/jpeg, 63k
Légende Figure 9.2: Soils and landscape in the semi-arid area
Crédits Source: Diagramme block source: Bourgeon G., 1991.
URL http://books.openedition.org/ifp/docannexe/image/10145/img-2.jpg
Fichier image/jpeg, 54k

Auteur

Professor at Etablissement National d’Enseignement Supérieur Agronomique de Dijon (ENESAD), France. He is a Soil Scientist who has been specializing in soil genesis and soil functioning under temperate and tropical climates. During the last 20 years in the French agronomic research institute (INRA) he has been focusing on soil quality and soil and water relationship in intensive farming systems of Western Europe. He was Head of Laboratory of Soil Sciences, French Institute of Pondicherry (2000-2002). He has published about 40 articles in international journals and has managed 2 multidisciplinary research projects in the areas of soil quality, intensive agriculture and environment.

© Institut Français de Pondichéry, 2003

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