Towards New Cropping Systems

Agriculture in the twenty-first century will have to make its contribution to the reduction of GHG emissions (principally CO2, CH4, N2O) but also and above all to adapt to climate change to continue to satisfy the vital needs of populations in food, energy, fibers, and other products. The end results and priorities will depend on the regions of the Earth concerned. It is clear that the global reduction of agriculture contribution in the production of GHG will be a priority for the developed countries. Most of the less developed countries in the tropical areas will still have the problem - and for some with increased intensity - of the absolute necessity of producing various food products for local and remote consumption. This context, of course, relates to world economic and legal situations, but also necessitates specific research efforts in the development of sustainable systems, mobilising agronomists and agrometeorologists alike. Regarding the reduction of GHG emission and the storage of carbon in the agro-ecosystems, the necessity for research on the measurement of GHG emissions and storage has already been mentioned. It must be carried out for the existing ecosystems but also evaluate any new systems proposed. For several years, reduced tillage techniques combined with the use of mulches and ground cover plants (no tillage techniques, conservation agriculture) have undergone major development in various parts of the world (for example Brazil, United States, Canada) and may enable an increase in soil carbon storage and a reduction of erosion. However, the global assessment towards GHG still remains to be made, as well as the sustainability capacity of these systems. In the same way, the development of agroforestry systems may contribute to an increase of the quantity of carbon fixed in the soils and biomass, a reduction of the quantity of fossil fuel used for soil tillage operations, a reduction in the use of pesticides and also a stabilisation of the ecosystem in the face of climatic variability. It is, however, often difficult to persuade farmers to adopt these often promising solutions for various economic or social reasons. It is therefore important to use integrated approaches, which take into account the farmers' decision-making process, to design operational systems (Boiffin et al., 2001). Moreover the development of innovative systems necessarily combines experimentation on the ground and complex models with varied but coupled processes. For example the construction of models simulating the response of flooded rice-production systems to climatic change would involve to take into account the modification of CO2 content and temperature on all physiological processes (photosynthesis, transpiration, phenology or ripening) and the effect of changes in practices (sowing date, density, varietal choice, fertilisation, management of groundwater) on the elaboration of yield and the emission of GHG (here CH4).

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