Emissões gasosas medidas em campos regados de arroz produzido em dois solos diferentes, em Portugal, por efeito das práticas culturais, do clima e do aumento da concentração de CO2 na atmosfera

Gaseous N emissions have been rarely measured in irrigated crops in Southern European countries. Under well-drained aerobic soil conditions, NO is the dominant gas produced from nitrification. Under wetter conditions, N2O+N2 from nitrification+denitrification become the dominant gases. Greenhouse gases (GHGs) (NO+N2O) are both temporarily and spatially variable and can be promoted by N and C additions (Carranca, 1996). In flooded rice fields, intermittent drainage and aeration is useful to reduce the emission of CH4, another important GHG. However, after flooding of intermittently drained soils, enhanced N2O emissions can be observed. Ammonia losses may also occur for a period of 7-14 days after NH4+ fertilizer is added and can be as large as 60% of fertilizer N depending on soil pH and NH4+ concentration, especially in floodwater, air temperature and wind speed (Mosier, 1999). A strategy to reduce N losses (gaseous and leaching) and improve fertilizer N use efficiency by irrigated rice crop is the incorporation of applied N below the soil surface and the use of NH4+ fertilizers. Soil microorganisms and plants can produce at least 400 different VOCs, (GHG) including aldehydes, ketones, organic acids, C2-C4 alkanes and alkenes, etc.. Rice crop emits VOCs which are responsible by flavour and play an important role in its susceptibility and defense against insects (Maes and Debergh, 2003). Infected plants emit more volatiles than healthy plants. This study will evaluate the environmental consequences of the interactive effects of land-use practices [water regime, fertilizer placement and type, soil type (sandy and clay soils), microbial activity] climate (temperature), and atmospheric composition of CO2 by the production of gaseous NOx (NO, N2O), NH3, CO2, CH4, and a wide range of VOCs, and on irrigated rice growth and yield cropped at Salvaterra de Magos (Lisboa e Vale do Tejo region), over two consecutive years.
In the experiment, N and C fluxes (gaseous emissions, mineralization, nitrification, NH4+ fixation, leaching), and microbial population (biomass and activity) will be measured in two contrasting soils cultivated with flooded rice (Oryza sativa L. Eurosis) in open field and open chambers, in three replicated plots, for two years. In clay soil, closed chambers enriched with double amount of CO2 concentration (atmospheric CO2 concentration will be controlled by fumigation) will be placed in each plot to evaluate the N and C fluxes and microbial activity and abundance, as well as the crop response in two years. These results will be compared with the data obtained under the normal climatic conditions. The team involved in these studies have good knowledge and the institutions are well equipped to run the experiments. The Consultant is an expert on flux measurements and will help on interpretation of data of gas emissions taking into account the IPPC rules (IPPC, 1997).