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Università di Napoli "Federico II" (2007)

Denitrifier and nitrifier activities and N2O fluxes of fine and coarse textured soils of a mediterranean irrigated cropland in southern Italy

Forte, Annachiara

Titre : Denitrifier and nitrifier activities and N2O fluxes of fine and coarse textured soils of a mediterranean irrigated cropland in southern Italy

Auteur : Forte, Annachiara

Université de soutenance : Università di Napoli "Federico II"

Grade : Tesi di dottorato 2007

Résumé partiel
Nitrous oxide (N2O) is a climate relevant trace gas, moreover involved in the depletion of stratospheric ozone. Although in the last decades the increased N-input and the large use of irrigation, have greatly increased N2O emissions from croplands (actually contributing about 50 % of the global anthropogenic N2O emissions), only scanty data about N2O fluxes are available up to the present from irrigated croplands of Mediterranean countries, despite the extention of these cropped surface areas, and this is limiting to provide the necessary information in order to validate models predicting N2O fluxes at a global scale. It’s well known that denitrification and nitrification are the main natural sources of this trace gas and, if N-fertilizers are not used efficiently, great loss of nitrogen can occur via both these processes. Moreover recent studies pointed out the importance to take into account biological parameters such as denitrifier and nitrifier activities in order to develop more reliable N2O fluxes models. In this study nitrous oxide emissions, denitrifying and nitrifying activities and their different contribution to N2O production, were measured in an irrigated cropland in Campania Region (South Italy), with the aim to determine how the changing environmental climate conditions and the agriculture management practices can affect soil bacterial processes and the amount of N2O evolved by, under Mediterannean climate conditions. The experimental site, contributing to the FLUXNET network, is the agricultural field of a buffalo zootechnic farm, characterized by an alluvial soil with both clay (relating to most of the cropped surface) and sandy profile inside the same field. Dairy farms are a typical component of the overall regional agricultural section and show a relevant potential for N losses via soil denitrifying and nitrifying activities, since they produce a great amount of organic waste, generally applied as fertilizer N to the cropped soil, and largely relay on irrigation practice to grow fodder plants for animal consumption. Both monitoring activities and a manipulation experiment were carried out in the agricultural field. As far as concern the monitoring activities, measurements of denitrification rate (AIT on intact soil cores) and N2O fluxes from soil (Static manual chambers) were carried out for the clay soil through the course of the Lolium italicum crop (Sep ’04 - Apr ’05) and the Zea mays growths both in 2005 and 2006 (May ’05 - Aug ’05). Similar analyses were performed at the sandy site during the winter grass cultivation and the maize crop in 2005, to investigate possible differences between fine and coarse textured soils. At that time also measurements of net nitrification rate (Buried-bag method by intact soil cores) were carried out for both profiles, moreover at the sandy site the relative nitrifier and denitrifier contributions to N2O fluxes from soil were investigated as well (Short exposure to acetylene method adapted for intact soil cores). By the manipulation experiment, the effects of different amounts of urea N fertilizer (higher urea N supply N+ and lower urea N supply N- than the rest of the field C) on denitrifying activity and N2O emission from the fine textured soil were tested at the late fertilization time during the maize crop in 2005, in restricted plots inside the agricultural field where determinations of nitrogen metabolism of maize plants were carried out as well (Arena, pers.comm. ; Parisi et al., 2006). The monitoring study showed considerable denitrifying activities (up to about 1500 µg N2O- N m-2 h-1) and N2O fluxes from soil (up to 570 µg N2O- N m-2 h-1) in the course of the maize cropping cycles, soon after irrigation events following fertilizer N applications, clearly as a result of the combined enhancing effects of high soil temperatures and not limiting soil nitrates and WFPS’s. Anyway different patterns between clay and sandy soils were noticed according to their different physico-chemical characteristics.


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