**Acknowledgements**

*Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…*

ria, when reduction is high.

changes and migration routes.

sion support systems [20].

systems and their evolution in the long term.

because the soil is a nonrenewable capital at human scale.

short-time processes in agro- and ecosystems.

**6. Conclusions**

green rust fougerite, when reduction is moderate, and sulfide versus sulfate equilib-

Agriculture evolving from organic to mineral farming since 10,000 years has greatly increased its performance and has capacity to feed humanity. Geochemistry combined with other disciplines, such as palynology, bioclimatology, mineralogy, etc., offers cutting edge methods to investigate both long-time, medium-time, and

The long-term investigations show that soils and sediments have recorded agropastoral activities and thus paleo-agriculture can be studied. The combination of global climatic events (temperature deduced from ice cores), storm activities, and relative sea level movements led to socioeconomic destabilization of the local society and impacted the sustainability of agriculture in these remote times. This has led to a renewal of historical studies, integrating the above cited disciplines and others, especially genomics with DNA analyses and identification of mutations, anthropology, and archeology. Emblematic events in the history of mankind were recently revisited: late Bronze Age collapse of civilization mentioned above [5], shedding light on the mysterious invasions of the "Peoples of the Sea," and very recently the fall of the Roman Empire [19]: here too, e.g., isotope geochemistry (10Be) was used to reconstruct variations of solar irradiance. According to this study [19], climatic changes combined with apparition of three successive pandemias (first pest due to *Yersinia*, under emperor Justinian) are facilitated by commercial routes connecting tropical regions in Africa to the Mediterranean, from the Caspian Sea to Scotland. Eventually, economic (including monetary), political troubles, and migrations of peoples from Asian steppes to the West due to climatic change led to wars and the ultimate collapse of the Roman Empire. It appears then that multidisciplinary studies nowadays extensively use geochemistry not only to precise datation but to reconstruct climatic

In the present concern about climate change, it is important to stress that it is multifactorial and such studies necessitate decades of cooperation. They point too to the factors that increase the resilience of societies toward external forcings and help to detect tipping points and to build scenarios that can be integrated in deci-

Medium-term investigations, particularly for agro-systems, are difficult to perform because data are scarce: the time step for an agronomist or a farmer is most often the cultural year. The medium-term investigations of the grasslands in Crau area show that Craponne's irrigation network has built up the soils in Crau by silt depositions since the sixteenth century. Since 60 years, the hay quality remains constant. Water quality remains constant along the year and contributes directly to the plant nutrition. This irrigated agro-system has mitigated until today the temperature increase, around 2°C, observed in this

In situ instrumentation and sensors allow us to address dynamics at two scales that escape to classical agronomic analysis: slow drifts and high-frequency events (pulses). In particular the continuous monitoring of master variables of soil solution can record these events and help us to understand the dynamics of agro-

This kind of information is needed to manage the sustainability of agro-systems

**80**

area.

The authors thank the following PhD students for their contribution: L. Cary, F. Feder, and G. Mohammed. They thank also M. Mayor, A. Régeard, and G. Sévenier for their help as technical support for chemical analysis and field monitoring.
