MODELLING CARBON AND NITROGEN DYNAMICS IN PADDY RICE SYSTEM: IMPACTS ON CROP PRODUCTIVITY AND GREENHOUSE GAS EMISSIONS

The main challenge of modern agriculture lies in the need of enhancing crop productivity to guarantee food security while achieving the sustainability of cropping systems in a changing climate. In a recent speech to the 21st Conference of Parties to the United Nations Framework Convention on Climate Change (COP21) held in Paris, the president of the United States declared that for all the challenges we face, the growing threat of climate change could define the contours of this century more dramatically than any other. This is why He hopes that all the countries in the world, united in common effort and by a common purpose, will not condemn the next generation to a planet that’s beyond its capacity to repair. Agricultural activities deep influence the carbon, water and nutrients cycles at global level, then still play a vital role in the survival of humankind. The need to double food production by 2050 is entrusted to agriculture, which accounts for 14% of greenhouse gases emission and is considered as the economic sector most uniquely susceptible to changes in climate patterns, due to its dependence on the biophysical environment. Standing first among all food grain crops, rice (Oryza sativa L.) is in the spotlight due to the projected decrease in production in top producing countries and to the environmental sustainability of rice cropping systems, in light of the use of large amount of water for irrigation and of the contribution to the emission of greenhouse gases (GHGs) at the global level. The improvement of the water and nutrient management in paddy rice cropping systems is then considered as a necessary step to mitigate agriculture’s GHG emissions, as reported by the United Nations Foundation. The scaling up of mitigation strategies from farmers’ level to national policy makers needs the support of the scientific community, who is in charge to develop research to address these paramount questions. In this framework, the adoption of cropping system simulation models as a reference to assess both the productivity and the environmental impacts of cropping systems under a variety of management and climatic scenarios seems unavoidable, as they are the only available tools to reproduce the nonlinear responses of biophysical processes to boundary conditions. They also represent a viable solution to design and test alternate strategies to mitigate the emission of GHGs and to optimize the use and management of resources in agriculture. This PhD program enables the scientific community to move forward the integration of available biophysical models to dynamically simulate the different components of the rice cropping system, considering the multiple, mutual interactions among system’s domains which determine rice crop yield and environmental drawbacks. The final achievement is the delivery of a software targeting this purpose, which is documented in the last chapter; the objective of this research product is to give a modelling solution to simulate the comprehensive set of biophysical processes involved with the paddy rice cropping system, considering the crop development and growth, the soil water dynamics, the effects of fertilizers on nitrogen leaching and the emission of greenhouse gases at field scale, considering the impact of alternate farmer management strategies. During the work some deficiencies in current models were highlighted and solved, such as the unjustified complexity of widely adopted crop simulators or the lack, within them, of algorithms for the simulation of processes which significantly contribute to explain the variability of rice yield. The output of this work is made available through software components and modular modelling solutions: this choice, representing the state of the art of software engineering science, removes technological bottlenecks which usually prevent advances in agricultural system modelling and fosters international collaborations between research centers while laying the basis for further developments.