Digital Theses Archive


Tesi etd-11042016-180752

Type of thesis
E-mail address
Evaluation of alternative cropping systems for the mitigation of nitrous oxide emissions (N2O) in a Mediterranean environment
Scientific disciplinary sector
relatore Prof. BONARI, ENRICO
  • CO2
  • crop yield
  • durum wheat
  • faba bean
  • flow-through non-steady state chamber technique
  • greenhouse gas emissions
  • mineral nitrogen
  • minimum tillage
  • N2 biological fixation
  • nitrification inhibitor
  • nitrogen balance
  • nitrogen fertilization
  • NOE model
  • soil flux
  • soil WFPS
  • sunflower
  • urease inhibitor
Exam session start date
To prevent irreversible changes of the global climate the Intergovernmental Panel on Climate Change stated on 2014 that is required to reach about zero emissions of long-lived greenhouse gases by the end of the century. As a consequence, also the agricultural sector that is a source of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), must plays its role in the mitigation of its emissions. In particular, the attention of researchers is pointed on N2O emissions, as this gas is ozone depleting, long lasting in atmosphere (about 121 years) and its global warming potential is about 298 times higher respect to CO2. Moreover, N2O is most relevant in regard to agriculture since is mainly emitted from soil as a product of microbiological processes involved in the biogeochemical nitrogen (N) cycle. Soil parameters and microbiological processes in soil may be affected by agricultural practices, i.e.: N fertilizer rate, type of N fertilizer, tillage intensity, crop residues management etc. Therefore, considering the necessity to feed 9 billion people by 2050, there is a need to deeply understand the N2O production processes and individuate agricultural practices that may, at the same time, limit N2O emissions without negatively affect the yield of the crops. Moreover, as N2O emissions are closely related to pedoclimatic conditions the effect of the agricultural practices on N2O emissions is site-specific. The majority of the studies investigating the sources of N2O emissions in agricultural land were mainly conducted in temperate climates, so the uncertainty in the mitigation potential of the agricultural practices is mainly relevant for Mediterranean environments. This thesis is aimed at investigating the dependency of N2O emissions on environmental conditions and agricultural practices, in the cultivation of arable crops in a Mediterranean environment, and at individuating N2O mitigation practices that may guarantee yield conservation. In particular, Chapters 2, 3 and 4 are related to results of field experiments where N2O monitoring was carried out for two years with an innovative mobile instrument developed within the LIFE+ IPNOA project. In Chapter 2 are presented results concerning soil N2O emissions monitored in durum wheat with the aim to test the effect of tillage intensity and N fertilization rate on soil N2O emissions. Moreover, the Nitrous Oxide Emissions (NOE) model was applied to test its suitability to estimate N2O emissions in a Mediterranean condition. Main results highlighted: a close dependence of N2O emissions on rainfall, a significant reduction of N2O emissions reducing N fertilizer rate without affecting grain yield and a good capability of NOE to estimate cumulative N2O emissions. In Chapter 3, are presented results of a field experiment carried out on a biennial durum wheat-sunflower rotation with the aims to assess the effect of tillage depth and N fertilizer rate on N2O emissions and yield of the two crops. Another objective was to evaluate the rotation as a whole, analyzing the cropping systems at different agricultural intensification levels in term of grain yield, cumulative N2O emissions, emission factors and N balance to individuate the best intensification level to mitigate N2O emissions and guarantee the crops yield maximization. Main results highlighted at cropping systems level that minimum tillage together with the application of the highest N fertilizer rate, provided highest crops yield reducing N2O emissions by about 30% respect to ploughing. Chapter 4 presents results of a field experiment on faba bean with the aim to assess the N2O emissions magnitude and the nitrogen fixation on a leguminous crop in relation to tillage system. Main results highlighted a significant effect of tillage depth on N2O emissions, in particular minimum tillage reduced N2O emissions by 60-80% respect to ploughing, optimizing at the same time crop yield. Moreover, it was identified a correlation between cumulative N2O emissions and the percentage of N in plants derived by nitrogen fixation. <br>The last chapter presenting experimental results is Chapter 5, in which are presented results of laboratory experiments conducted to analyse the effect on N2O emissions of the N fertilizer type on two different textured soils. Two laboratory experiments on soil cores were conducted to assess the effect on N2O emissions of i) ammonium or nitrate-based fertilizers at different water filled pores space (WFPS) levels and ii) N fertilizers with and without nitrification or urease inhibitors. Results highlighted highest emissions from ammonium-based fertilizer and the stimulating effect of WFPS on N2O. Moreover, the nitrification inhibitors showed a mitigation potential of N2O emissions closely related to soil properties, while urease inhibitors did not mitigate N2O in both soils. <br>Results presented in this thesis allowed to clarify the dependency of N2O emissions on N fertilizer type, N rate, tillage intensity and environmental variables and to suggest strategies for N2O mitigation in a Mediterranean environment with attention on crops yield optimization.<br>