Modelling long-term dynamics of nitrogen and carbon in intensive rice (wheat) production systems in the Indo-Gangetic plain

To judge the sustainability of agricultural production systems, the processes determining production and the quality of the natural resources (soils, water and air), as influenced by environmental conditions and management practices, should be understood quantitatively. An experimental approach to this problem is problematic: it requires long-term experimentation, which is laborious and time-consuming, takes too long to yield relevant results within the timeframe of the present priorities and allows study of only a limited number of alternatives. Moreover, the erratic and unpredictable nature of environmental conditions (particularly the weather) makes it difficult to use time- and location-specific information for extrapolation and prediction. A systems approach, in which existing knowledge is harnessed into quantitative, explanatory models, is therefore attractive. Such models should be calibrated and validated on the basis of results of long-term experiments (or time-series of relevant system characteristics), and can then be used to explore (technical) options and constraints for the development and implementation of sustainable agricultural systems. The quality of the natural resources, particularly the soil, and associated crop performance, are affected by many interacting processes, governed by environmental conditions, and soil and crop management. In recent years, much attention has been paid to the sustainability of intensive rice production systems, including rice-wheat rotations, with emphasis on the effects of these practices on resource quality. Exploration of the long-term effects of environmental conditions and crop and soil management on resource qualities and the associated yield potentials and input requirements, requires a summary model, in which all relevant processes and interactions are incorporated in a descriptive, rather than an explanatory fashion, and whose data requirements can be readily satisfied. This research project aims at development, testing and application of a summary model of the interactions and feed backs between soil and crop management, soil quality characteristics (particularly nitrogen and carbon contents), crop yields and quality. The model will be developed and tested for the plot level, as a basis for further scaling up, in later stages to the farm and regional levels.In the first stage of the project, an exhaustive review is made of existing models at various degrees of complexity that deal with (parts of) the system under consideration. The review will include an inventory of available long-term data sets that are available for model calibration and/or validation. For the relevant processes, generally acceptable descriptions are then selected, adapted and/or developed, for construction, calibration and validation of the summary model.