Agro-environmental performance of alternative agronomic practices for improving the sustainability of temperate rice cropping systems

Rice cultivation in temperate agro-ecosystems will face numerous challenges in the coming decades to increase its agro-environmental sustainability. In an effort to increase crop yields and improve production efficiency, conventional agricultural practices often have a major impact on the natural environment. Therefore, there is a need to develop and introduce new strategies that allow rational and optimal use of water and land resources to adapt to climate change and reduce impacts on the environment. In this context, this thesis focused primarily on the adoption of alternate wetting and drying (AWD), a water-saving technique that alternates periods of flooding with periods of drying during the cropping cycle. Attention was also devoted to alternative techniques for paddy soil management particularly conservation tillage (i.e. minimum and no tillage). The aims of this thesis were: (i) to evaluate the impact of AWD on rice agronomic performances, grain quality and greenhouse gas (GHG) emissions; (ii) to assess the influence of water management on the availability of nitrogen (N) for plant uptake from different sources, including mineral N fertilizers, in order to limit losses and optimize N uptake and use efficiency; (iii) to investigate the influences of conservation tillage practices on rice productivity and soil organic carbon (C) stock in the medium-term. This thesis demonstrated that AWD has the potential to mitigate GHG emissions from paddy fields while maintaining optimal agronomic performance in temperate rice cropping systems. Therefore, AWD may represent a viable alternative to continuous flooding to improve the agro-environmental sustainability of temperate rice cropping systems. The important insights provided regarding the infuence of water, crop 2 residue and N fertilization management and their interaction on the contribution of different N sources to plant uptake may contribute to identify suitable fertilization practices that favour plant N uptake during the early stages of rice growth under AWD. Conservation tillage can contribute to increase sustainability of temperate rice systems. Minimum tillage uses production resources more efficiently compared to conventional tillage (i.e. ploughing) and sustains soil fertility by promoting organic matter and N inputs, facilitating soil aggregation and preventing soil compaction. No tillage has some limitations that hinders its adoption, such us yield reductions and excessive soil compaction. The present thesis demonstrated that higher yields and increased resource-use efficiencies are not necessarily conflicting goals in rice cultivation. This work provides useful insights at field scale, providing a holistic evaluation and leading to the quantification of key agro-ecological indicators which can be of extreme importance for the management of temperate rice cropping systems. Therefore, the understandings and results obtained in this thesis provide practical implications on innovative management of rice paddies.